Topics

locked Slightly OT: How can I dissolve Potting Compound? FOLLOWUP


 

Thank you one and all for your suggestions on removing the potting. Your
suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs based on
your advice.
2) Heat. This seemed like a slightly better approach than the chemical one.

But before I get to what happened when I applied heat I learned many new
things along the way thanks to a few of our members and especially, Ed
Breya. Ed's comments explained in detail how these HV potted power supplies
worked. That led me to an amazing web site that has a staggering amount of
information on them about every aspect of lasers of all kinds including
their HV Power Supplies. If anyone is interested the site is
https://www.repairfaq.org/sam/laserfil.htm
I have to caution you that I spent hours roaming around in all Sam had to
say. He is an incredible resource for anyone who owns a laser. I found many
different power supply circuits and details about laser HV modules which is
what I apparently blew out that prompted me to ask about removing the
potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful potted
HV laser supply I had. It was going to try and force too much current
through the spectrum tubes so I added additional ballast resistors and
connected it to a Variac so I had some control over the High Voltage and the
constant current With this arrangement I was able to test every one of the
spectrum tubes (I have over 20 different ones each containing a different
gas) to determine their breakdown voltage and their steady state current
requirements. That told me what I should be looking for to replace the Laser
HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of my
failed HV Laser supply so for $15 I bought a toaster oven at a thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and poked it
with a sharp tool. Nothing happened. At 250F (120C) it got a little softer
and a few cracks appeared. At 300F (150C) I was able to chip off the bottom
and see the solder side of the PCB. A few of the sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature knob
from the angle I was standing but I raised the temperature once again by the
same amount.

30 minutes later when I checked on it, it was smoking. I would rather not
say what the reading on the thermocouple was but I will tell you it was way
over 260C (500F). When I touched the potting the PC board fell away from the
rest of the potting. I knew immediately that was to be expected since solder
melts at a lot less than 260C. The parts fell away from the epoxy, by
barely touching them but of course there was no way to know what they used
to be connected to anymore. The entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals to
remove potting but realistically even with carefully controlled heat potting
is not going to give up its secrets easily or cleanly. I now have an "oven"
I can use for soldering surface mount parts with whenever I find something I
can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV Power
Supply for my Spectrum Tubes in the form of the Jim William's Linear
Technology Application Note 49, August 1992, titled "Illumination Circuitry
for Liquid Crystal Displays". His design is shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance Variable
Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dennis
Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don’t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF







--
Dennis Tillman W7pF
TekScopes Moderator


Ed Breya
 

This reminds me of similar experience I had and discussed here a couple years ago, trying to un-pot or un-coat various ferrite transformers, in order to reuse the cores and bobbins. I tried a number of chemical methods, and also my lab oven, with varying degrees of success. Heating worked the best, with decent results around 250-350 F. I managed to get a fair number apart OK, and save the bobbins too, but generally the cores could be saved only if the adhesives let go sufficiently, and the bobbins tended to be deformed or ruined by the solvents or heat, or fall apart while prying the cores out.

Even with all that, there were some with (non-silicone) coatings and goops that were impervious to the nastiest solvents on hand, and would not let go after hours of baking at 500 deg F, the hottest the oven could go. The bobbins were destroyed, and the cores too, because they couldn't be pried apart without breaking. There's some tough stuff out there.

BTW Dennis, I had replied a few weeks back, to your private email about the laser PS stuff, with some more thoughts - I hope you got it.

Ed


Redguuz
 

Hi,

Epoxies are thermoharders, which means that, once set (from mixing 2 base components) , you cannot melt them any more (unlike thermoplast e.g. poly ethylene, PVC, Polypropylene), see also

https://en.wikipedia.org/wiki/Epoxy

So meltingan epoxy potted circuit, by applying heat is impossible (same story for other well known thermoharders loike bakelite, nitrilrubbers etc.).You cannot melt car tyres.

Also Epoxies are chemically very inert (so dissolving it with nasty chemicals is not only very dangerous but would dissolve the components you are looking at.

Judiciously softening epoxy potted circuits by heat can be done (see photo of a "depotted"Motorcycle / aeroplane voltage regulator),but you have to control the temperature much better than you did (your temperature steps were too coarse) and it takes a lot of "Elbow Grease".


-
 

Dennis,

A friend of mine is always disassembling things and reverse engineering
them so I sent your message to him. He replied and that me that one of the
guys that he used with work with at Litton Laser told him that he used to
removing potting compound by dipping the item into liquid Nitrogen and
leaving it there until the nitrogen quit boiling and then took it out and
tapped it with a hammer and that the coating would shatter and fail off. I
have to wonder what that treatment would do to the plastic bodies of
transistors and other items but it might be worth a try. IMO you might need
to leave the item in the liquid Nitrogen for a bit less time to prevent the
plastic items from getting too cold and too hard and brittle. But the good
thing about this method is that there are no dangerous chemicals to deal
with and even the liquid Nitrogen just boils away so there's nothing to
dispose of except the potting compound itself.

FWIW

On Sun, Feb 21, 2021 at 3:37 PM Dennis Tillman W7pF <dennis@ridesoft.com>
wrote:

Thank you one and all for your suggestions on removing the potting. Your
suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs based on
your advice.
2) Heat. This seemed like a slightly better approach than the chemical one.

But before I get to what happened when I applied heat I learned many new
things along the way thanks to a few of our members and especially, Ed
Breya. Ed's comments explained in detail how these HV potted power supplies
worked. That led me to an amazing web site that has a staggering amount of
information on them about every aspect of lasers of all kinds including
their HV Power Supplies. If anyone is interested the site is
https://www.repairfaq.org/sam/laserfil.htm
I have to caution you that I spent hours roaming around in all Sam had to
say. He is an incredible resource for anyone who owns a laser. I found many
different power supply circuits and details about laser HV modules which is
what I apparently blew out that prompted me to ask about removing the
potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful potted
HV laser supply I had. It was going to try and force too much current
through the spectrum tubes so I added additional ballast resistors and
connected it to a Variac so I had some control over the High Voltage and
the
constant current With this arrangement I was able to test every one of the
spectrum tubes (I have over 20 different ones each containing a different
gas) to determine their breakdown voltage and their steady state current
requirements. That told me what I should be looking for to replace the
Laser
HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of my
failed HV Laser supply so for $15 I bought a toaster oven at a thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and poked it
with a sharp tool. Nothing happened. At 250F (120C) it got a little softer
and a few cracks appeared. At 300F (150C) I was able to chip off the bottom
and see the solder side of the PCB. A few of the sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature knob
from the angle I was standing but I raised the temperature once again by
the
same amount.

30 minutes later when I checked on it, it was smoking. I would rather not
say what the reading on the thermocouple was but I will tell you it was way
over 260C (500F). When I touched the potting the PC board fell away from
the
rest of the potting. I knew immediately that was to be expected since
solder
melts at a lot less than 260C. The parts fell away from the epoxy, by
barely touching them but of course there was no way to know what they used
to be connected to anymore. The entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals to
remove potting but realistically even with carefully controlled heat
potting
is not going to give up its secrets easily or cleanly. I now have an "oven"
I can use for soldering surface mount parts with whenever I find something
I
can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV Power
Supply for my Spectrum Tubes in the form of the Jim William's Linear
Technology Application Note 49, August 1992, titled "Illumination Circuitry
for Liquid Crystal Displays". His design is shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance Variable
Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dennis
Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs)
filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to
determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser
Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is
powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because
6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I
don’t
know much about this matching the power supply to the tube. All I do know
is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF







--
Dennis Tillman W7pF
TekScopes Moderator






Chuck Harris <cfharris@...>
 

I de-pot epoxy potted assemblies frequently, and I use heat.

First, I put the device in my environmental chamber set for
150C. When it is good and hot, I bring it to my bench, and
use a combination of a 1/8" blade screwdriver, and the hot
air gun from my SMD rework station (set to 300C). When it
starts to get too hard to pick at, it goes back into the
environmental chamber for a while...

I pick at the epoxy, which the heat has turned into a rubber
eraser consistency, while applying heat from my SMD hot air
gun. Usually a rocking motion with the blade of the screwdriver
works best (rotating back and forth so this edge, and then
that edge of the blade touches...). Spare your good and sharp
screwdrivers from this duty. One that has its edges worn
dull from years of use and abuse is best...

Elbow grease needs to be applied in copious amounts, though
not much force is necessary, you don't want to break stuff.

The epoxy generally releases from points of dissimilar materials
pretty easily... in other words, the epoxy bond sucks.

-Chuck Harris

Redguuz via groups.io wrote:

Hi,

Epoxies are thermoharders, which means that, once set (from mixing 2 base components) , you cannot melt them any more (unlike thermoplast e.g. poly ethylene, PVC, Polypropylene), see also

https://en.wikipedia.org/wiki/Epoxy

So meltingan epoxy potted circuit, by applying heat is impossible (same story for other well known thermoharders loike bakelite, nitrilrubbers etc.).You cannot melt car tyres.

Also Epoxies are chemically very inert (so dissolving it with nasty chemicals is not only very dangerous but would dissolve the components you are looking at.

Judiciously softening epoxy potted circuits by heat can be done (see photo of a "depotted"Motorcycle / aeroplane voltage regulator),but you have to control the temperature much better than you did (your temperature steps were too coarse) and it takes a lot of "Elbow Grease".









Chuck Harris <cfharris@...>
 

In my experience, there is epoxy, and there is EPOXY!

The stuff used on IC's, is EPOXY! The stuff used for
potting generally has additives that make it epoxy.

One thing they don't want to happen in potted assemblies
is for EPOXY! to grab onto a delicate part and break it
from thermal expansion/contraction. So, the additives
make the resulting product less apt to bond well, and a bit
flexible.

Comic Red Green once said... actually he always said:
"Duct Tape! is there anything you can't do with it?"

I think the same applies to LN2. When you have a large
dewar of LN2 in your lab, frittering itself away into
nothingness, you tend to find ways of using it before its
cold leaks out. Fun ensues!

-Chuck Harris

- wrote:

Dennis,

A friend of mine is always disassembling things and reverse engineering
them so I sent your message to him. He replied and that me that one of the
guys that he used with work with at Litton Laser told him that he used to
removing potting compound by dipping the item into liquid Nitrogen and
leaving it there until the nitrogen quit boiling and then took it out and
tapped it with a hammer and that the coating would shatter and fail off. I
have to wonder what that treatment would do to the plastic bodies of
transistors and other items but it might be worth a try. IMO you might need
to leave the item in the liquid Nitrogen for a bit less time to prevent the
plastic items from getting too cold and too hard and brittle. But the good
thing about this method is that there are no dangerous chemicals to deal
with and even the liquid Nitrogen just boils away so there's nothing to
dispose of except the potting compound itself.

FWIW

On Sun, Feb 21, 2021 at 3:37 PM Dennis Tillman W7pF <dennis@ridesoft.com>
wrote:

Thank you one and all for your suggestions on removing the potting. Your
suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs based on
your advice.
2) Heat. This seemed like a slightly better approach than the chemical one.

But before I get to what happened when I applied heat I learned many new
things along the way thanks to a few of our members and especially, Ed
Breya. Ed's comments explained in detail how these HV potted power supplies
worked. That led me to an amazing web site that has a staggering amount of
information on them about every aspect of lasers of all kinds including
their HV Power Supplies. If anyone is interested the site is
https://www.repairfaq.org/sam/laserfil.htm
I have to caution you that I spent hours roaming around in all Sam had to
say. He is an incredible resource for anyone who owns a laser. I found many
different power supply circuits and details about laser HV modules which is
what I apparently blew out that prompted me to ask about removing the
potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful potted
HV laser supply I had. It was going to try and force too much current
through the spectrum tubes so I added additional ballast resistors and
connected it to a Variac so I had some control over the High Voltage and
the
constant current With this arrangement I was able to test every one of the
spectrum tubes (I have over 20 different ones each containing a different
gas) to determine their breakdown voltage and their steady state current
requirements. That told me what I should be looking for to replace the
Laser
HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of my
failed HV Laser supply so for $15 I bought a toaster oven at a thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and poked it
with a sharp tool. Nothing happened. At 250F (120C) it got a little softer
and a few cracks appeared. At 300F (150C) I was able to chip off the bottom
and see the solder side of the PCB. A few of the sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature knob
from the angle I was standing but I raised the temperature once again by
the
same amount.

30 minutes later when I checked on it, it was smoking. I would rather not
say what the reading on the thermocouple was but I will tell you it was way
over 260C (500F). When I touched the potting the PC board fell away from
the
rest of the potting. I knew immediately that was to be expected since
solder
melts at a lot less than 260C. The parts fell away from the epoxy, by
barely touching them but of course there was no way to know what they used
to be connected to anymore. The entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals to
remove potting but realistically even with carefully controlled heat
potting
is not going to give up its secrets easily or cleanly. I now have an "oven"
I can use for soldering surface mount parts with whenever I find something
I
can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV Power
Supply for my Spectrum Tubes in the form of the Jim William's Linear
Technology Application Note 49, August 1992, titled "Illumination Circuitry
for Liquid Crystal Displays". His design is shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance Variable
Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dennis
Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs)
filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to
determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser
Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is
powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because
6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I
don’t
know much about this matching the power supply to the tube. All I do know
is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF







--
Dennis Tillman W7pF
TekScopes Moderator










 

Very clever! I never thought of that. There was a time I could have done this and I know exactly how it works.
Yes, there is a risk, but as you point out it involves no dangerous chemicals or careful temperature regulation and messy chipping away of very hot epoxy.
Thanks for the suggestion even if it is too late in my case.
Dennis Tilman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of -
Sent: Monday, February 22, 2021 3:49 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting Compound? FOLLOWUP

Dennis,

A friend of mine is always disassembling things and reverse engineering them so I sent your message to him. He replied and that me that one of the guys that he used with work with at Litton Laser told him that he used to removing potting compound by dipping the item into liquid Nitrogen and leaving it there until the nitrogen quit boiling and then took it out and tapped it with a hammer and that the coating would shatter and fail off. I have to wonder what that treatment would do to the plastic bodies of transistors and other items but it might be worth a try. IMO you might need to leave the item in the liquid Nitrogen for a bit less time to prevent the plastic items from getting too cold and too hard and brittle. But the good thing about this method is that there are no dangerous chemicals to deal with and even the liquid Nitrogen just boils away so there's nothing to dispose of except the potting compound itself.

FWIW

On Sun, Feb 21, 2021 at 3:37 PM Dennis Tillman W7pF <dennis@ridesoft.com>
wrote:

Thank you one and all for your suggestions on removing the potting.
Your suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs
based on your advice.
2) Heat. This seemed like a slightly better approach than the chemical one.

But before I get to what happened when I applied heat I learned many
new things along the way thanks to a few of our members and
especially, Ed Breya. Ed's comments explained in detail how these HV
potted power supplies worked. That led me to an amazing web site that
has a staggering amount of information on them about every aspect of
lasers of all kinds including their HV Power Supplies. If anyone is
interested the site is https://www.repairfaq.org/sam/laserfil.htm
I have to caution you that I spent hours roaming around in all Sam had
to say. He is an incredible resource for anyone who owns a laser. I
found many different power supply circuits and details about laser HV
modules which is what I apparently blew out that prompted me to ask
about removing the potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful
potted HV laser supply I had. It was going to try and force too much
current through the spectrum tubes so I added additional ballast
resistors and connected it to a Variac so I had some control over the
High Voltage and the constant current With this arrangement I was able
to test every one of the spectrum tubes (I have over 20 different ones
each containing a different
gas) to determine their breakdown voltage and their steady state
current requirements. That told me what I should be looking for to
replace the Laser HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of
my failed HV Laser supply so for $15 I bought a toaster oven at a thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and
poked it with a sharp tool. Nothing happened. At 250F (120C) it got a
little softer and a few cracks appeared. At 300F (150C) I was able to
chip off the bottom and see the solder side of the PCB. A few of the sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature
knob from the angle I was standing but I raised the temperature once
again by the same amount.

30 minutes later when I checked on it, it was smoking. I would rather
not say what the reading on the thermocouple was but I will tell you
it was way over 260C (500F). When I touched the potting the PC board
fell away from the rest of the potting. I knew immediately that was to
be expected since solder melts at a lot less than 260C. The parts
fell away from the epoxy, by barely touching them but of course there
was no way to know what they used to be connected to anymore. The
entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals
to remove potting but realistically even with carefully controlled
heat potting is not going to give up its secrets easily or cleanly. I
now have an "oven"
I can use for soldering surface mount parts with whenever I find
something I can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV
Power Supply for my Spectrum Tubes in the form of the Jim William's
Linear Technology Application Note 49, August 1992, titled
"Illumination Circuitry for Liquid Crystal Displays". His design is shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance
Variable Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Dennis Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would appreciate any suggestions on what works to do this. I’m
guessing it may be epoxy. I stuck the tip of a hot soldering iron in
it for a few seconds without much effect.

When it was working it turned out to be perfect for powering gas
filled Spectrum Tubes. These spectrum tubes (smaller versions of neon
signs) filled with a variety of gasses are an excellent source of
spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas
in the spectrum tube conducts the voltage across the gas drops (250V
to 450V for
example) and unless you limit the current (to a few mA) it will
destroy the tube. Can anyone can point me to a source of information
on how to determine the proper voltage and current I need to power
these spectrum tubes? Is there a web site or group devoted to Spectrum
Tubes?

Something happened to the inverter and it stopped working. The input
is now open. The inverter is a black potted brick 3” x 1½” x 1”. The
ballast resistor has continuity so that is not the problem. The
original label on the inverter is partially destroyed so I can’t tell
what its initial high voltage output was or what it current limits at.
All I do know is that it was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser
Drive Inc. asking if they could tell me the output voltage and
limiting current but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can
figure out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is
powered by 115VAC. It puts out 2350VDC at 6.5mA. This causes the
Spectrum Tubes to flicker. They do not run continuously. I am guessing
that this because 6.5mA is more current than the tube can conduct. The
amount of current the tube draws increases in proportion to the inside
diameter of the tube but I don’t know much about this matching the
power supply to the tube. All I do know is the one that went bad seems
to be an ideal match for the spectrum tubes I have.

Battery operated (DC input) inverters are much more desirable than AC
input inverters for this application because the AC rectification and
poor filtering shows up on the output DC as significant ripple causing
the amplitude of each spectral line to be blurred.

Dennis Tillman W7pF







--
Dennis Tillman W7pF
TekScopes Moderator











--
Dennis Tillman W7pF
TekScopes Moderator


Paul Amaranth
 

LN2 is apparently pretty cheap if you have a supplier to sell it to you.
I knew I should have picked up a dewar from the university surplus store
in the old times. If they ever open it up again ...

Paul

On Mon, Feb 22, 2021 at 10:40:26AM -0800, Dennis Tillman W7pF wrote:
Very clever! I never thought of that. There was a time I could have done this and I know exactly how it works.
Yes, there is a risk, but as you point out it involves no dangerous chemicals or careful temperature regulation and messy chipping away of very hot epoxy.
Thanks for the suggestion even if it is too late in my case.
Dennis Tilman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of -
Sent: Monday, February 22, 2021 3:49 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting Compound? FOLLOWUP

Dennis,

A friend of mine is always disassembling things and reverse engineering them so I sent your message to him. He replied and that me that one of the guys that he used with work with at Litton Laser told him that he used to removing potting compound by dipping the item into liquid Nitrogen and leaving it there until the nitrogen quit boiling and then took it out and tapped it with a hammer and that the coating would shatter and fail off. I have to wonder what that treatment would do to the plastic bodies of transistors and other items but it might be worth a try. IMO you might need to leave the item in the liquid Nitrogen for a bit less time to prevent the plastic items from getting too cold and too hard and brittle. But the good thing about this method is that there are no dangerous chemicals to deal with and even the liquid Nitrogen just boils away so there's nothing to dispose of except the potting compound itself.

FWIW

On Sun, Feb 21, 2021 at 3:37 PM Dennis Tillman W7pF <dennis@ridesoft.com>
wrote:

Thank you one and all for your suggestions on removing the potting.
Your suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs
based on your advice.
2) Heat. This seemed like a slightly better approach than the chemical one.

But before I get to what happened when I applied heat I learned many
new things along the way thanks to a few of our members and
especially, Ed Breya. Ed's comments explained in detail how these HV
potted power supplies worked. That led me to an amazing web site that
has a staggering amount of information on them about every aspect of
lasers of all kinds including their HV Power Supplies. If anyone is
interested the site is https://www.repairfaq.org/sam/laserfil.htm
I have to caution you that I spent hours roaming around in all Sam had
to say. He is an incredible resource for anyone who owns a laser. I
found many different power supply circuits and details about laser HV
modules which is what I apparently blew out that prompted me to ask
about removing the potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful
potted HV laser supply I had. It was going to try and force too much
current through the spectrum tubes so I added additional ballast
resistors and connected it to a Variac so I had some control over the
High Voltage and the constant current With this arrangement I was able
to test every one of the spectrum tubes (I have over 20 different ones
each containing a different
gas) to determine their breakdown voltage and their steady state
current requirements. That told me what I should be looking for to
replace the Laser HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of
my failed HV Laser supply so for $15 I bought a toaster oven at a thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and
poked it with a sharp tool. Nothing happened. At 250F (120C) it got a
little softer and a few cracks appeared. At 300F (150C) I was able to
chip off the bottom and see the solder side of the PCB. A few of the sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature
knob from the angle I was standing but I raised the temperature once
again by the same amount.

30 minutes later when I checked on it, it was smoking. I would rather
not say what the reading on the thermocouple was but I will tell you
it was way over 260C (500F). When I touched the potting the PC board
fell away from the rest of the potting. I knew immediately that was to
be expected since solder melts at a lot less than 260C. The parts
fell away from the epoxy, by barely touching them but of course there
was no way to know what they used to be connected to anymore. The
entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals
to remove potting but realistically even with carefully controlled
heat potting is not going to give up its secrets easily or cleanly. I
now have an "oven"
I can use for soldering surface mount parts with whenever I find
something I can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV
Power Supply for my Spectrum Tubes in the form of the Jim William's
Linear Technology Application Note 49, August 1992, titled
"Illumination Circuitry for Liquid Crystal Displays". His design is shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance
Variable Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Dennis Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would appreciate any suggestions on what works to do this. I’m
guessing it may be epoxy. I stuck the tip of a hot soldering iron in
it for a few seconds without much effect.

When it was working it turned out to be perfect for powering gas
filled Spectrum Tubes. These spectrum tubes (smaller versions of neon
signs) filled with a variety of gasses are an excellent source of
spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas
in the spectrum tube conducts the voltage across the gas drops (250V
to 450V for
example) and unless you limit the current (to a few mA) it will
destroy the tube. Can anyone can point me to a source of information
on how to determine the proper voltage and current I need to power
these spectrum tubes? Is there a web site or group devoted to Spectrum
Tubes?

Something happened to the inverter and it stopped working. The input
is now open. The inverter is a black potted brick 3” x 1½” x 1”. The
ballast resistor has continuity so that is not the problem. The
original label on the inverter is partially destroyed so I can’t tell
what its initial high voltage output was or what it current limits at.
All I do know is that it was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser
Drive Inc. asking if they could tell me the output voltage and
limiting current but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can
figure out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is
powered by 115VAC. It puts out 2350VDC at 6.5mA. This causes the
Spectrum Tubes to flicker. They do not run continuously. I am guessing
that this because 6.5mA is more current than the tube can conduct. The
amount of current the tube draws increases in proportion to the inside
diameter of the tube but I don’t know much about this matching the
power supply to the tube. All I do know is the one that went bad seems
to be an ideal match for the spectrum tubes I have.

Battery operated (DC input) inverters are much more desirable than AC
input inverters for this application because the AC rectification and
poor filtering shows up on the output DC as significant ripple causing
the amplitude of each spectral line to be blurred.

Dennis Tillman W7pF







--
Dennis Tillman W7pF
TekScopes Moderator











--
Dennis Tillman W7pF
TekScopes Moderator







!DSPAM:6033fab334634654433166!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows


-
 

I passed up a good size dewar at a garage sale for $5 about a year and a
half ago! :-/ At the time I just thought that I'd never use it and I'm
getting to the age where I need to be getting rid of stuff instead of
acquiring more; so, for once, I listened to the logical half of my brain
instead of my imagination.

I had a mole removed a few years ago and the Dr used liquid Nitrogen and
he keeps his in one of the old green metal Aladdin thermos bottles like the
one that used to be sold with their metal lunch boxes. He said that that
thermos would keep some of the liquid N2 all day long. They only need a
tiny drop of it to freeze moles and warts. The thermos are small but they
might be large enough for a small assembly.

On Mon, Feb 22, 2021 at 1:46 PM Paul Amaranth <paul@auroragrp.com> wrote:

LN2 is apparently pretty cheap if you have a supplier to sell it to you.
I knew I should have picked up a dewar from the university surplus store
in the old times. If they ever open it up again ...

Paul

On Mon, Feb 22, 2021 at 10:40:26AM -0800, Dennis Tillman W7pF wrote:
Very clever! I never thought of that. There was a time I could have done
this and I know exactly how it works.
Yes, there is a risk, but as you point out it involves no dangerous
chemicals or careful temperature regulation and messy chipping away of very
hot epoxy.
Thanks for the suggestion even if it is too late in my case.
Dennis Tilman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of -
Sent: Monday, February 22, 2021 3:49 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting
Compound? FOLLOWUP

Dennis,

A friend of mine is always disassembling things and reverse
engineering them so I sent your message to him. He replied and that me that
one of the guys that he used with work with at Litton Laser told him that
he used to removing potting compound by dipping the item into liquid
Nitrogen and leaving it there until the nitrogen quit boiling and then took
it out and tapped it with a hammer and that the coating would shatter and
fail off. I have to wonder what that treatment would do to the plastic
bodies of transistors and other items but it might be worth a try. IMO you
might need to leave the item in the liquid Nitrogen for a bit less time to
prevent the plastic items from getting too cold and too hard and brittle.
But the good thing about this method is that there are no dangerous
chemicals to deal with and even the liquid Nitrogen just boils away so
there's nothing to dispose of except the potting compound itself.

FWIW

On Sun, Feb 21, 2021 at 3:37 PM Dennis Tillman W7pF <dennis@ridesoft.com

wrote:

Thank you one and all for your suggestions on removing the potting.
Your suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs
based on your advice.
2) Heat. This seemed like a slightly better approach than the chemical
one.

But before I get to what happened when I applied heat I learned many
new things along the way thanks to a few of our members and
especially, Ed Breya. Ed's comments explained in detail how these HV
potted power supplies worked. That led me to an amazing web site that
has a staggering amount of information on them about every aspect of
lasers of all kinds including their HV Power Supplies. If anyone is
interested the site is https://www.repairfaq.org/sam/laserfil.htm
I have to caution you that I spent hours roaming around in all Sam had
to say. He is an incredible resource for anyone who owns a laser. I
found many different power supply circuits and details about laser HV
modules which is what I apparently blew out that prompted me to ask
about removing the potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful
potted HV laser supply I had. It was going to try and force too much
current through the spectrum tubes so I added additional ballast
resistors and connected it to a Variac so I had some control over the
High Voltage and the constant current With this arrangement I was able
to test every one of the spectrum tubes (I have over 20 different ones
each containing a different
gas) to determine their breakdown voltage and their steady state
current requirements. That told me what I should be looking for to
replace the Laser HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I
had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of
my failed HV Laser supply so for $15 I bought a toaster oven at a
thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and
poked it with a sharp tool. Nothing happened. At 250F (120C) it got a
little softer and a few cracks appeared. At 300F (150C) I was able to
chip off the bottom and see the solder side of the PCB. A few of the
sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature
knob from the angle I was standing but I raised the temperature once
again by the same amount.

30 minutes later when I checked on it, it was smoking. I would rather
not say what the reading on the thermocouple was but I will tell you
it was way over 260C (500F). When I touched the potting the PC board
fell away from the rest of the potting. I knew immediately that was to
be expected since solder melts at a lot less than 260C. The parts
fell away from the epoxy, by barely touching them but of course there
was no way to know what they used to be connected to anymore. The
entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals
to remove potting but realistically even with carefully controlled
heat potting is not going to give up its secrets easily or cleanly. I
now have an "oven"
I can use for soldering surface mount parts with whenever I find
something I can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV
Power Supply for my Spectrum Tubes in the form of the Jim William's
Linear Technology Application Note 49, August 1992, titled
"Illumination Circuitry for Liquid Crystal Displays". His design is
shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance
Variable Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Dennis Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would appreciate any suggestions on what works to do this. I’m
guessing it may be epoxy. I stuck the tip of a hot soldering iron in
it for a few seconds without much effect.

When it was working it turned out to be perfect for powering gas
filled Spectrum Tubes. These spectrum tubes (smaller versions of neon
signs) filled with a variety of gasses are an excellent source of
spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas
in the spectrum tube conducts the voltage across the gas drops (250V
to 450V for
example) and unless you limit the current (to a few mA) it will
destroy the tube. Can anyone can point me to a source of information
on how to determine the proper voltage and current I need to power
these spectrum tubes? Is there a web site or group devoted to Spectrum
Tubes?

Something happened to the inverter and it stopped working. The input
is now open. The inverter is a black potted brick 3” x 1½” x 1”. The
ballast resistor has continuity so that is not the problem. The
original label on the inverter is partially destroyed so I can’t tell
what its initial high voltage output was or what it current limits at.
All I do know is that it was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser
Drive Inc. asking if they could tell me the output voltage and
limiting current but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can
figure out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is
powered by 115VAC. It puts out 2350VDC at 6.5mA. This causes the
Spectrum Tubes to flicker. They do not run continuously. I am guessing
that this because 6.5mA is more current than the tube can conduct. The
amount of current the tube draws increases in proportion to the inside
diameter of the tube but I don’t know much about this matching the
power supply to the tube. All I do know is the one that went bad seems
to be an ideal match for the spectrum tubes I have.

Battery operated (DC input) inverters are much more desirable than AC
input inverters for this application because the AC rectification and
poor filtering shows up on the output DC as significant ripple causing
the amplitude of each spectral line to be blurred.

Dennis Tillman W7pF







--
Dennis Tillman W7pF
TekScopes Moderator











--
Dennis Tillman W7pF
TekScopes Moderator







!DSPAM:6033fab334634654433166!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows






Chuck Harris <cfharris@...>
 

The large dewars are nice, but they have to have a very hard vacuum
inside if you want them to hold LN2 for any amount of time... We're
talking oil diffusion levels.

Then, there is the problem of getting your local supplier to let you
have some. They consider it rather dangerous, and most won't sell it
to individuals. So, become a company.

-Chuck Harris

- wrote:

I passed up a good size dewar at a garage sale for $5 about a year and a
half ago! :-/ At the time I just thought that I'd never use it and I'm
getting to the age where I need to be getting rid of stuff instead of
acquiring more; so, for once, I listened to the logical half of my brain
instead of my imagination.

I had a mole removed a few years ago and the Dr used liquid Nitrogen and
he keeps his in one of the old green metal Aladdin thermos bottles like the
one that used to be sold with their metal lunch boxes. He said that that
thermos would keep some of the liquid N2 all day long. They only need a
tiny drop of it to freeze moles and warts. The thermos are small but they
might be large enough for a small assembly.

On Mon, Feb 22, 2021 at 1:46 PM Paul Amaranth <paul@auroragrp.com> wrote:

LN2 is apparently pretty cheap if you have a supplier to sell it to you.
I knew I should have picked up a dewar from the university surplus store
in the old times. If they ever open it up again ...

Paul

On Mon, Feb 22, 2021 at 10:40:26AM -0800, Dennis Tillman W7pF wrote:
Very clever! I never thought of that. There was a time I could have done
this and I know exactly how it works.
Yes, there is a risk, but as you point out it involves no dangerous
chemicals or careful temperature regulation and messy chipping away of very
hot epoxy.
Thanks for the suggestion even if it is too late in my case.
Dennis Tilman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of -
Sent: Monday, February 22, 2021 3:49 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting
Compound? FOLLOWUP

Dennis,

A friend of mine is always disassembling things and reverse
engineering them so I sent your message to him. He replied and that me that
one of the guys that he used with work with at Litton Laser told him that
he used to removing potting compound by dipping the item into liquid
Nitrogen and leaving it there until the nitrogen quit boiling and then took
it out and tapped it with a hammer and that the coating would shatter and
fail off. I have to wonder what that treatment would do to the plastic
bodies of transistors and other items but it might be worth a try. IMO you
might need to leave the item in the liquid Nitrogen for a bit less time to
prevent the plastic items from getting too cold and too hard and brittle.
But the good thing about this method is that there are no dangerous
chemicals to deal with and even the liquid Nitrogen just boils away so
there's nothing to dispose of except the potting compound itself.

FWIW

On Sun, Feb 21, 2021 at 3:37 PM Dennis Tillman W7pF <dennis@ridesoft.com

wrote:

Thank you one and all for your suggestions on removing the potting.
Your suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs
based on your advice.
2) Heat. This seemed like a slightly better approach than the chemical
one.

But before I get to what happened when I applied heat I learned many
new things along the way thanks to a few of our members and
especially, Ed Breya. Ed's comments explained in detail how these HV
potted power supplies worked. That led me to an amazing web site that
has a staggering amount of information on them about every aspect of
lasers of all kinds including their HV Power Supplies. If anyone is
interested the site is https://www.repairfaq.org/sam/laserfil.htm
I have to caution you that I spent hours roaming around in all Sam had
to say. He is an incredible resource for anyone who owns a laser. I
found many different power supply circuits and details about laser HV
modules which is what I apparently blew out that prompted me to ask
about removing the potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful
potted HV laser supply I had. It was going to try and force too much
current through the spectrum tubes so I added additional ballast
resistors and connected it to a Variac so I had some control over the
High Voltage and the constant current With this arrangement I was able
to test every one of the spectrum tubes (I have over 20 different ones
each containing a different
gas) to determine their breakdown voltage and their steady state
current requirements. That told me what I should be looking for to
replace the Laser HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I
had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of
my failed HV Laser supply so for $15 I bought a toaster oven at a
thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and
poked it with a sharp tool. Nothing happened. At 250F (120C) it got a
little softer and a few cracks appeared. At 300F (150C) I was able to
chip off the bottom and see the solder side of the PCB. A few of the
sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature
knob from the angle I was standing but I raised the temperature once
again by the same amount.

30 minutes later when I checked on it, it was smoking. I would rather
not say what the reading on the thermocouple was but I will tell you
it was way over 260C (500F). When I touched the potting the PC board
fell away from the rest of the potting. I knew immediately that was to
be expected since solder melts at a lot less than 260C. The parts
fell away from the epoxy, by barely touching them but of course there
was no way to know what they used to be connected to anymore. The
entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals
to remove potting but realistically even with carefully controlled
heat potting is not going to give up its secrets easily or cleanly. I
now have an "oven"
I can use for soldering surface mount parts with whenever I find
something I can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV
Power Supply for my Spectrum Tubes in the form of the Jim William's
Linear Technology Application Note 49, August 1992, titled
"Illumination Circuitry for Liquid Crystal Displays". His design is
shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance
Variable Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Dennis Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would appreciate any suggestions on what works to do this. I’m
guessing it may be epoxy. I stuck the tip of a hot soldering iron in
it for a few seconds without much effect.

When it was working it turned out to be perfect for powering gas
filled Spectrum Tubes. These spectrum tubes (smaller versions of neon
signs) filled with a variety of gasses are an excellent source of
spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas
in the spectrum tube conducts the voltage across the gas drops (250V
to 450V for
example) and unless you limit the current (to a few mA) it will
destroy the tube. Can anyone can point me to a source of information
on how to determine the proper voltage and current I need to power
these spectrum tubes? Is there a web site or group devoted to Spectrum
Tubes?

Something happened to the inverter and it stopped working. The input
is now open. The inverter is a black potted brick 3” x 1½” x 1”. The
ballast resistor has continuity so that is not the problem. The
original label on the inverter is partially destroyed so I can’t tell
what its initial high voltage output was or what it current limits at.
All I do know is that it was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser
Drive Inc. asking if they could tell me the output voltage and
limiting current but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can
figure out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is
powered by 115VAC. It puts out 2350VDC at 6.5mA. This causes the
Spectrum Tubes to flicker. They do not run continuously. I am guessing
that this because 6.5mA is more current than the tube can conduct. The
amount of current the tube draws increases in proportion to the inside
diameter of the tube but I don’t know much about this matching the
power supply to the tube. All I do know is the one that went bad seems
to be an ideal match for the spectrum tubes I have.

Battery operated (DC input) inverters are much more desirable than AC
input inverters for this application because the AC rectification and
poor filtering shows up on the output DC as significant ripple causing
the amplitude of each spectral line to be blurred.

Dennis Tillman W7pF







--
Dennis Tillman W7pF
TekScopes Moderator











--
Dennis Tillman W7pF
TekScopes Moderator







!DSPAM:6033fab334634654433166!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows










shalopt
 

The stainless steel lifetime warranty ones. I have 4, two I pickup at yard sales
duds Aladdin replaced. Have another dud one of the original.
They will keep Hot coffee drinkable for about 12 hours.
gary g


-
 

I have welding equipment including Oxy-Acetylene and Helium, CO2 and
25/75 gas for MIG and TIG and the same companies sell all of that also sell
liquified gasses so I doubt that I'd have any trouble getting liquid N2.
Liquid O2, possibly, but not liquid N2 which in realtively inert and
doesn't support combustion.

On Mon, Feb 22, 2021 at 9:31 PM Chuck Harris <cfharris@erols.com> wrote:

The large dewars are nice, but they have to have a very hard vacuum
inside if you want them to hold LN2 for any amount of time... We're
talking oil diffusion levels.

Then, there is the problem of getting your local supplier to let you
have some. They consider it rather dangerous, and most won't sell it
to individuals. So, become a company.

-Chuck Harris

- wrote:
I passed up a good size dewar at a garage sale for $5 about a year and
a
half ago! :-/ At the time I just thought that I'd never use it and I'm
getting to the age where I need to be getting rid of stuff instead of
acquiring more; so, for once, I listened to the logical half of my brain
instead of my imagination.

I had a mole removed a few years ago and the Dr used liquid Nitrogen
and
he keeps his in one of the old green metal Aladdin thermos bottles like
the
one that used to be sold with their metal lunch boxes. He said that that
thermos would keep some of the liquid N2 all day long. They only need a
tiny drop of it to freeze moles and warts. The thermos are small but they
might be large enough for a small assembly.

On Mon, Feb 22, 2021 at 1:46 PM Paul Amaranth <paul@auroragrp.com>
wrote:

LN2 is apparently pretty cheap if you have a supplier to sell it to you.
I knew I should have picked up a dewar from the university surplus store
in the old times. If they ever open it up again ...

Paul

On Mon, Feb 22, 2021 at 10:40:26AM -0800, Dennis Tillman W7pF wrote:
Very clever! I never thought of that. There was a time I could have
done
this and I know exactly how it works.
Yes, there is a risk, but as you point out it involves no dangerous
chemicals or careful temperature regulation and messy chipping away of
very
hot epoxy.
Thanks for the suggestion even if it is too late in my case.
Dennis Tilman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of -
Sent: Monday, February 22, 2021 3:49 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting
Compound? FOLLOWUP

Dennis,

A friend of mine is always disassembling things and reverse
engineering them so I sent your message to him. He replied and that me
that
one of the guys that he used with work with at Litton Laser told him
that
he used to removing potting compound by dipping the item into liquid
Nitrogen and leaving it there until the nitrogen quit boiling and then
took
it out and tapped it with a hammer and that the coating would shatter
and
fail off. I have to wonder what that treatment would do to the plastic
bodies of transistors and other items but it might be worth a try. IMO
you
might need to leave the item in the liquid Nitrogen for a bit less time
to
prevent the plastic items from getting too cold and too hard and
brittle.
But the good thing about this method is that there are no dangerous
chemicals to deal with and even the liquid Nitrogen just boils away so
there's nothing to dispose of except the potting compound itself.

FWIW

On Sun, Feb 21, 2021 at 3:37 PM Dennis Tillman W7pF <
dennis@ridesoft.com

wrote:

Thank you one and all for your suggestions on removing the potting.
Your suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs
based on your advice.
2) Heat. This seemed like a slightly better approach than the chemical
one.

But before I get to what happened when I applied heat I learned many
new things along the way thanks to a few of our members and
especially, Ed Breya. Ed's comments explained in detail how these HV
potted power supplies worked. That led me to an amazing web site that
has a staggering amount of information on them about every aspect of
lasers of all kinds including their HV Power Supplies. If anyone is
interested the site is https://www.repairfaq.org/sam/laserfil.htm
I have to caution you that I spent hours roaming around in all Sam had
to say. He is an incredible resource for anyone who owns a laser. I
found many different power supply circuits and details about laser HV
modules which is what I apparently blew out that prompted me to ask
about removing the potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful
potted HV laser supply I had. It was going to try and force too much
current through the spectrum tubes so I added additional ballast
resistors and connected it to a Variac so I had some control over the
High Voltage and the constant current With this arrangement I was able
to test every one of the spectrum tubes (I have over 20 different ones
each containing a different
gas) to determine their breakdown voltage and their steady state
current requirements. That told me what I should be looking for to
replace the Laser HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I
had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of
my failed HV Laser supply so for $15 I bought a toaster oven at a
thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and
poked it with a sharp tool. Nothing happened. At 250F (120C) it got a
little softer and a few cracks appeared. At 300F (150C) I was able to
chip off the bottom and see the solder side of the PCB. A few of the
sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature
knob from the angle I was standing but I raised the temperature once
again by the same amount.

30 minutes later when I checked on it, it was smoking. I would rather
not say what the reading on the thermocouple was but I will tell you
it was way over 260C (500F). When I touched the potting the PC board
fell away from the rest of the potting. I knew immediately that was to
be expected since solder melts at a lot less than 260C. The parts
fell away from the epoxy, by barely touching them but of course there
was no way to know what they used to be connected to anymore. The
entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals
to remove potting but realistically even with carefully controlled
heat potting is not going to give up its secrets easily or cleanly. I
now have an "oven"
I can use for soldering surface mount parts with whenever I find
something I can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV
Power Supply for my Spectrum Tubes in the form of the Jim William's
Linear Technology Application Note 49, August 1992, titled
"Illumination Circuitry for Liquid Crystal Displays". His design is
shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance
Variable Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Dennis Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would appreciate any suggestions on what works to do this. I’m
guessing it may be epoxy. I stuck the tip of a hot soldering iron in
it for a few seconds without much effect.

When it was working it turned out to be perfect for powering gas
filled Spectrum Tubes. These spectrum tubes (smaller versions of neon
signs) filled with a variety of gasses are an excellent source of
spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas
in the spectrum tube conducts the voltage across the gas drops (250V
to 450V for
example) and unless you limit the current (to a few mA) it will
destroy the tube. Can anyone can point me to a source of information
on how to determine the proper voltage and current I need to power
these spectrum tubes? Is there a web site or group devoted to Spectrum
Tubes?

Something happened to the inverter and it stopped working. The input
is now open. The inverter is a black potted brick 3” x 1½” x 1”. The
ballast resistor has continuity so that is not the problem. The
original label on the inverter is partially destroyed so I can’t tell
what its initial high voltage output was or what it current limits at.
All I do know is that it was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser
Drive Inc. asking if they could tell me the output voltage and
limiting current but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can
figure out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is
powered by 115VAC. It puts out 2350VDC at 6.5mA. This causes the
Spectrum Tubes to flicker. They do not run continuously. I am guessing
that this because 6.5mA is more current than the tube can conduct. The
amount of current the tube draws increases in proportion to the inside
diameter of the tube but I don’t know much about this matching the
power supply to the tube. All I do know is the one that went bad seems
to be an ideal match for the spectrum tubes I have.

Battery operated (DC input) inverters are much more desirable than AC
input inverters for this application because the AC rectification and
poor filtering shows up on the output DC as significant ripple causing
the amplitude of each spectral line to be blurred.

Dennis Tillman W7pF







--
Dennis Tillman W7pF
TekScopes Moderator











--
Dennis Tillman W7pF
TekScopes Moderator







!DSPAM:6033fab334634654433166!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows














Chuck Harris <cfharris@...>
 

A poorly serviced dewar full of LN2, riding in the back seat
of your car, will quite easily snuff your life out, without
you ever even knowing there is a problem...

Your welding gas cylinders won't do that.

-Chuck Harris

- wrote:

I have welding equipment including Oxy-Acetylene and Helium, CO2 and
25/75 gas for MIG and TIG and the same companies sell all of that also sell
liquified gasses so I doubt that I'd have any trouble getting liquid N2.
Liquid O2, possibly, but not liquid N2 which in realtively inert and
doesn't support combustion.


-
 

Wrong, I think that a poorly secured welding cylinder riding in the
backseat of a car would easily snuff the life out of you if you ran into
something. IMO You would have to be very, very, stupid to carry something
like that inside of your car; for a variety of reasons. People have also
been known to blow up their cars due to leaking cylinders of acetylene and
the like and people have been made sick and probably even killed due to
suffocation hazards from gas cylinders in many kinds of enclosed spaces.
Regardless, I NEVER carry gas cylinders inside of a car and I would not
carry any liquified gas there either. My cylinders get carried, *strapped
down*, in the *open* back of a truck or a trailer. No exceptions. The same
with hazardous liquids like gasoline, MEK and acetone, etc. BLEVE? No
thanks! Among other things, I've had teachers and friends that have seen
cylinders dropped and the necks broken off and they have described how far
a 200+ pound heavy steel cylinder can fly and the damage that it will do
when it gets stopped!

BTW I used to live only a few miles from where that Blue Rhino propane
plant in Florida caught fire and exploded a few years ago and I watched as
it repeatedly exploded a few years ago so I know what even propane can do.
Also in around 1974 I was also living quite near Antelope, California when
a train load of 500 pound bombs destined for VietNam caught fire and the
bombs started exploding! I had returned from VietNam only days before and
I instantly knew what that sound was! I do play with explosives and very
large fireworks (I'm a member of the largest Pyrotechnics club in the US)
as well as welding gasses and various chemicals but you can bet your asz
that I THINK about what I'm doing and I don't take unnecessary risks.

On Tue, Feb 23, 2021 at 6:33 AM Chuck Harris <cfharris@erols.com> wrote:

A poorly serviced dewar full of LN2, riding in the back seat
of your car, will quite easily snuff your life out, without
you ever even knowing there is a problem...

Your welding gas cylinders won't do that.

-Chuck Harris

- wrote:
I have welding equipment including Oxy-Acetylene and Helium, CO2 and
25/75 gas for MIG and TIG and the same companies sell all of that also
sell
liquified gasses so I doubt that I'd have any trouble getting liquid N2.
Liquid O2, possibly, but not liquid N2 which in realtively inert and
doesn't support combustion.





Chuck Harris <cfharris@...>
 

I found your trigger... good for me.

In taking offense, you miss the point completely, and reinforce
the reason why many suppliers of compressed and liquefied gasses
won't deal with non-business entities.

-Chuck Harris

- wrote:

Wrong, I think that a poorly secured welding cylinder riding in the
backseat of a car would easily snuff the life out of you if you ran into
something. IMO You would have to be very, very, stupid to carry something
like that inside of your car; for a variety of reasons. People have also
been known to blow up their cars due to leaking cylinders of acetylene and
the like and people have been made sick and probably even killed due to
suffocation hazards from gas cylinders in many kinds of enclosed spaces.
Regardless, I NEVER carry gas cylinders inside of a car and I would not
carry any liquified gas there either. My cylinders get carried, *strapped
down*, in the *open* back of a truck or a trailer. No exceptions. The same
with hazardous liquids like gasoline, MEK and acetone, etc. BLEVE? No
thanks! Among other things, I've had teachers and friends that have seen
cylinders dropped and the necks broken off and they have described how far
a 200+ pound heavy steel cylinder can fly and the damage that it will do
when it gets stopped!

BTW I used to live only a few miles from where that Blue Rhino propane
plant in Florida caught fire and exploded a few years ago and I watched as
it repeatedly exploded a few years ago so I know what even propane can do.
Also in around 1974 I was also living quite near Antelope, California when
a train load of 500 pound bombs destined for VietNam caught fire and the
bombs started exploding! I had returned from VietNam only days before and
I instantly knew what that sound was! I do play with explosives and very
large fireworks (I'm a member of the largest Pyrotechnics club in the US)
as well as welding gasses and various chemicals but you can bet your asz
that I THINK about what I'm doing and I don't take unnecessary risks.

On Tue, Feb 23, 2021 at 6:33 AM Chuck Harris <cfharris@erols.com> wrote:

A poorly serviced dewar full of LN2, riding in the back seat
of your car, will quite easily snuff your life out, without
you ever even knowing there is a problem...

Your welding gas cylinders won't do that.

-Chuck Harris

- wrote:
I have welding equipment including Oxy-Acetylene and Helium, CO2 and
25/75 gas for MIG and TIG and the same companies sell all of that also
sell
liquified gasses so I doubt that I'd have any trouble getting liquid N2.
Liquid O2, possibly, but not liquid N2 which in realtively inert and
doesn't support combustion.









Cliff Barber
 

Hi,I have only just discovered this thread. So I know I am too late. But.... I can assure you that a very "Common Chemical", one that you are will have in your vehicle will destroy epoxy. That chemical is Unleaded Petrol (Gasoline). Sadly, the addition of Ethanol to automobile fuel has caused the failure of the fuel tanks in some aircraft. Including CFM Shadow aircraft.
The epoxy bond is slowly degraded and eventually fails. Allowing the fuel to escape.. Not good. 
I would be interested to hear if anyone is willing to experiment with Ethanol / or Unleaded Fuel as a "solvent" for Epoxy.Good luckCliff  G4BGP

On Tuesday, 23 February 2021, 15:45:43 GMT, Chuck Harris <cfharris@erols.com> wrote:

I found your trigger... good for me.

In taking offense, you miss the point completely, and reinforce
the reason why many suppliers of compressed and liquefied gasses
won't deal with non-business entities.

-Chuck Harris

- wrote:
    Wrong, I think that a poorly secured welding cylinder riding in the
backseat of a car would easily snuff the life out of you if you ran into
something. IMO You would have to be very, very, stupid to carry something
like that inside of your car; for a variety of reasons.  People have also
been known to blow up their cars due to leaking cylinders of acetylene and
the like and people have been made sick and probably even killed due to
suffocation hazards from gas cylinders in many kinds of enclosed spaces.
Regardless, I NEVER carry gas cylinders inside of a car and I would not
carry any liquified gas there either.  My cylinders get carried, *strapped
down*, in the *open* back of a truck or a trailer. No exceptions. The same
with hazardous liquids like gasoline, MEK and acetone, etc.  BLEVE?  No
thanks!  Among other things, I've had teachers and friends that have seen
cylinders dropped and the necks broken off and they have described how far
a 200+ pound heavy steel cylinder can fly and the damage that it will do
when it gets stopped!

    BTW I used to live only a few miles from where that Blue Rhino propane
plant in Florida caught fire and exploded a few years ago and I watched as
it repeatedly exploded a few years ago so I know what even propane can do.
Also in around 1974 I was also living quite near Antelope, California when
a train load of 500 pound bombs destined for VietNam caught fire and the
bombs started exploding!  I had returned from VietNam only days before and
I instantly knew what that sound was!  I do play with explosives and very
large fireworks (I'm a member of the largest Pyrotechnics club in the US)
as well as welding gasses and various chemicals but you can bet your asz
that I THINK about what I'm doing and I don't take unnecessary risks.

On Tue, Feb 23, 2021 at 6:33 AM Chuck Harris <cfharris@erols.com> wrote:

A poorly serviced dewar full of LN2, riding in the back seat
of your car, will quite easily snuff your life out, without
you ever even knowing there is a problem...

Your welding gas cylinders won't do that.

-Chuck Harris

- wrote:
  I have welding equipment including Oxy-Acetylene and Helium, CO2 and
25/75 gas for MIG and TIG and the same companies sell all of that also
sell
liquified gasses so I doubt that I'd have any trouble getting liquid N2.
Liquid O2, possibly, but not liquid N2 which in realtively inert and
doesn't support combustion.









Chuck Harris <cfharris@...>
 

I have to say that I made that discovery several years ago.

The floats in the carburetors of my old engines are all soldered
together brass construction. Since the advent of first the oxygenated
gasoline, and later the ethanol additive, the floats have been getting
squished, like the air was sucked out of them.

Never being able to find any leaks, I figured that the brass walls had
thinned due to chemical etching, and were now too thin to handle normal
barometric changes, so I removed their vent's solder plugs, blew them
back up with compressed air, and soldered the vent holes closed. [The
vents are there so the floats can be soldered, and not have a partial
vacuum occur as the air inside cools back to room temperature.]

As an attempt to strengthen the floats, I cleaned them really well,
and then dipped them in epoxy. I figured the epoxy would both seal
any pinholes, and increase the wall thickness slightly.

Well, after one season, the engines started to flood the float bowls,
and inspection revealed that the epoxy was left in sheets in the
float bowl.

So, yes, epoxy is no longer gasoline proof. Its dissolution is a very
slow process, though.

-Chuck Harris.

Cliff Barber via groups.io wrote:

Hi,I have only just discovered this thread. So I know I am too late. But.... I can assure you that a very "Common Chemical", one that you are will have in your vehicle will destroy epoxy. That chemical is Unleaded Petrol (Gasoline). Sadly, the addition of Ethanol to automobile fuel has caused the failure of the fuel tanks in some aircraft. Including CFM Shadow aircraft.
The epoxy bond is slowly degraded and eventually fails. Allowing the fuel to escape.. Not good. 
I would be interested to hear if anyone is willing to experiment with Ethanol / or Unleaded Fuel as a "solvent" for Epoxy.Good luckCliff  G4BGP


-
 

"I found your trigger... good for me.

In taking offense, you miss the point completely, and reinforce
the reason why many suppliers of compressed and liquefied gasses
won't deal with non-business entities."

Sorry, you didn't find my trigger or you would know that you did with
absolutely no uncertainty. As for "good for me", well that shows a
considerable amount of immaturity on your part and says far more about you
than it does me. And no, I didn't "miss the point". Your point was as
clear then as it is now and I just wanted to point out that I have
CONSIDERABLE experience in this area. I also have considerable more
experience with related equipment than what I discussed but that was in
regards to my work for the US (and other) governments so I don't talk about
any of that, PERIOD.

As for me taking "offense", well maybe. But I usually do take offense to
loudmouths that don't know what they're talking about so I don't see that
as being a negative.

But to get to the bottom line, YES, most air gas suppliers WILL sell
liquefied gases to individuals just the same as they will sell them
compressed gasses. I have bought it and friends of mine have bought it.
OTOH there are some air gas suppliers that won't sell *anything* to
individuals. But that is just about their sales policy and not something
particular to liquified gasses.

If you really care to be informed on the subject, which I doubt, then go
over to the WeldingWeb forum. They maintain a running list of suppliers
that will or won't sell to individuals. <https://www.weldingweb.com/vbb/>
I'm one of the members there and on a few other welding forums.

Cheers,

On Tue, Feb 23, 2021 at 10:45 AM Chuck Harris <cfharris@erols.com> wrote:

I found your trigger... good for me.

In taking offense, you miss the point completely, and reinforce
the reason why many suppliers of compressed and liquefied gasses
won't deal with non-business entities.

-Chuck Harris

- wrote:
Wrong, I think that a poorly secured welding cylinder riding in the
backseat of a car would easily snuff the life out of you if you ran into
something. IMO You would have to be very, very, stupid to carry something
like that inside of your car; for a variety of reasons. People have also
been known to blow up their cars due to leaking cylinders of acetylene
and
the like and people have been made sick and probably even killed due to
suffocation hazards from gas cylinders in many kinds of enclosed spaces.
Regardless, I NEVER carry gas cylinders inside of a car and I would not
carry any liquified gas there either. My cylinders get carried,
*strapped
down*, in the *open* back of a truck or a trailer. No exceptions. The
same
with hazardous liquids like gasoline, MEK and acetone, etc. BLEVE? No
thanks! Among other things, I've had teachers and friends that have seen
cylinders dropped and the necks broken off and they have described how
far
a 200+ pound heavy steel cylinder can fly and the damage that it will do
when it gets stopped!

BTW I used to live only a few miles from where that Blue Rhino propane
plant in Florida caught fire and exploded a few years ago and I watched
as
it repeatedly exploded a few years ago so I know what even propane can
do.
Also in around 1974 I was also living quite near Antelope, California
when
a train load of 500 pound bombs destined for VietNam caught fire and the
bombs started exploding! I had returned from VietNam only days before
and
I instantly knew what that sound was! I do play with explosives and very
large fireworks (I'm a member of the largest Pyrotechnics club in the US)
as well as welding gasses and various chemicals but you can bet your asz
that I THINK about what I'm doing and I don't take unnecessary risks.

On Tue, Feb 23, 2021 at 6:33 AM Chuck Harris <cfharris@erols.com> wrote:

A poorly serviced dewar full of LN2, riding in the back seat
of your car, will quite easily snuff your life out, without
you ever even knowing there is a problem...

Your welding gas cylinders won't do that.

-Chuck Harris

- wrote:
I have welding equipment including Oxy-Acetylene and Helium, CO2 and
25/75 gas for MIG and TIG and the same companies sell all of that also
sell
liquified gasses so I doubt that I'd have any trouble getting liquid
N2.
Liquid O2, possibly, but not liquid N2 which in realtively inert and
doesn't support combustion.













Chuck Harris <cfharris@...>
 

Ah, I have met your sort a thousand times over.

Thanks for making it clear to me that there is less
to you than I ever could have imagined.

-Chuck Harris

- wrote:

Sorry, you didn't find my trigger or you would know that you did with
absolutely no uncertainty. As for "good for me", well that shows a
considerable amount of immaturity on your part and says far more about you
than it does me. And no, I didn't "miss the point". Your point was as
clear then as it is now and I just wanted to point out that I have
CONSIDERABLE experience in this area. I also have considerable more
experience with related equipment than what I discussed but that was in
regards to my work for the US (and other) governments so I don't talk about
any of that, PERIOD.


Dave Seiter
 

That's fine if you have a truck; some of us don't have the option, and no, we're NOT stupid!  Get off your high horse!
-Dave

On Tuesday, February 23, 2021, 07:22:41 AM PST, - <rrrr6789@gmail.com> wrote:

    Wrong, I think that a poorly secured welding cylinder riding in the
backseat of a car would easily snuff the life out of you if you ran into
something. IMO You would have to be very, very, stupid to carry something
like that inside of your car; for a variety of reasons.  People have also
been known to blow up their cars due to leaking cylinders of acetylene and
the like and people have been made sick and probably even killed due to
suffocation hazards from gas cylinders in many kinds of enclosed spaces.
Regardless, I NEVER carry gas cylinders inside of a car and I would not
carry any liquified gas there either.  My cylinders get carried, *strapped
down*, in the *open* back of a truck or a trailer. No exceptions. The same
with hazardous liquids like gasoline, MEK and acetone, etc.  BLEVE?  No
thanks!  Among other things, I've had teachers and friends that have seen
cylinders dropped and the necks broken off and they have described how far
a 200+ pound heavy steel cylinder can fly and the damage that it will do
when it gets stopped!

  BTW I used to live only a few miles from where that Blue Rhino propane
plant in Florida caught fire and exploded a few years ago and I watched as
it repeatedly exploded a few years ago so I know what even propane can do.
Also in around 1974 I was also living quite near Antelope, California when
a train load of 500 pound bombs destined for VietNam caught fire and the
bombs started exploding!  I had returned from VietNam only days before and
I instantly knew what that sound was!  I do play with explosives and very
large fireworks (I'm a member of the largest Pyrotechnics club in the US)
as well as welding gasses and various chemicals but you can bet your asz
that I THINK about what I'm doing and I don't take unnecessary risks.

On Tue, Feb 23, 2021 at 6:33 AM Chuck Harris <cfharris@erols.com> wrote:

A poorly serviced dewar full of LN2, riding in the back seat
of your car, will quite easily snuff your life out, without
you ever even knowing there is a problem...

Your welding gas cylinders won't do that.

-Chuck Harris

- wrote:
  I have welding equipment including Oxy-Acetylene and Helium, CO2 and
25/75 gas for MIG and TIG and the same companies sell all of that also
sell
liquified gasses so I doubt that I'd have any trouble getting liquid N2.
Liquid O2, possibly, but not liquid N2 which in realtively inert and
doesn't support combustion.