#### 1502 TDR Battery problems

Chuck Harris

OK, fair enough.

The circuit description tells us the average current out
of the charger is 150ma... regardless of the charge state
of the battery pack.

It also tells us it is a pulse charger, so, it could be creating
larger current pulses, as long as the average is 150ma.

A quick look at the schematic shows the transformer secondary
is connected directly (+/- a current shunt resistor) to the
Nicad pack. The SCR triggers every cycle where the average
current is below 150ma, and doesn't trigger when the average
current is above 150ma.

One thing that any engineer who has worked with nicad packs
knows is Nicads are wily beasts. They short circuit, and they
open circuit, almost at will.

Another thing they know is Nicad's are very, very low impedance
devices, and will not easily be bullied into going above about
1.7V/cell... especially at 1/10th C (trickle) charging rate.

I can't see any risk in trying. The 12V 2-5W zener will have
much higher resistance than the 1AH Nicad pack.

Quick calculation: P = I x E = 0.15A x 12V = 1.8W max zener
dissipation.

-Chuck Harris

The Nicad pack is
Tom Gardner wrote:

On 11/06/20 17:24, Chuck Harris wrote:
How is a zener dissipating the power necessary to get the
voltage down to 12V any different from a shunt resistor dissipating
the power necessary to get the voltage down to 12V?
A fair question.

My reticence is based on not having thought through how the "unique" characteristics
of the 1502's charging circuit interact with a resistor or clamp.

Consider the /hypothetical/ example where a charging circuit had a 16V output and a
very low output impedance.
With a resistor R, the max dissipation would be 16*16/R W.
With a clamp it would be determined by the clamp's impedance, which ought to be much
lower than R. Hence the current might be much higher than 16/R and the power
dissipation correspondingly higher.

The magnitude of any such effect would depend on the detailed operation of the
charging circuit, which I haven't considered in this context.

Seems to me they are both the same, and both dissipating the same
power the nicad pack is taking in.  Granted, a charging nicad pack
is endothermic, and a resistor is exothermic...
And the case is tightly sealed. Measurement would be required!

-Chuck Harris

Tom Gardner wrote:
On 11/06/20 16:02, Mark Pilant wrote:
I tried for quite a while to get the "battery fooler" to work *reliably* in
the 1502 and 1503 I have.  I was never successful.
Ditto.

The zener concept isn't too bad, but there is the power dissipation in the enclosed
volume.

I did try the Batteries Plus route and had them make up a replacement pack.
While it looked fine, it wouldn't fit.  The original Tek design used flat
top "C" cells, and pretty much all that is available are button top "C"
cells.  According to the specifications I could find, the "original" flat
top "C" cells were slightly shorter than the button top "C" cells; by the
height of the button.
I have found these acceptable
https://www.batteriesplus.co.uk/acatalog/1.2V_NiCd_Sub_C_Rechargeable_Tagged_Batteries.html

The diameter is slightly too small, but that is easily rectified with some
closed-cell foam.

BTW, I did some checking, and these batteries will last about a month before
needing to be recharged when "sitting" in TDR that has been turned off.
Yes. There is an ~1mA (higher if the chart recorder is present) drain even with the
front panel switch off. If the battery is left in then eventually one or more of the
cells will be damaged by being reverse charged. That's the reason the manual
specified the battery should be charged monthly.

Personally I just leave the battery pack out of the case. If I wanted to keep it in
the case, e.g. for shipping or long-term storage, then I would remove the fuse in the
battery pack.

Tom Gardner

On 11/06/20 17:24, Chuck Harris wrote:
How is a zener dissipating the power necessary to get the
voltage down to 12V any different from a shunt resistor dissipating
the power necessary to get the voltage down to 12V?
A fair question.

My reticence is based on not having thought through how the "unique" characteristics of the 1502's charging circuit interact with a resistor or clamp.

Consider the /hypothetical/ example where a charging circuit had a 16V output and a very low output impedance.
With a resistor R, the max dissipation would be 16*16/R W.
With a clamp it would be determined by the clamp's impedance, which ought to be much lower than R. Hence the current might be much higher than 16/R and the power dissipation correspondingly higher.

The magnitude of any such effect would depend on the detailed operation of the charging circuit, which I haven't considered in this context.

Seems to me they are both the same, and both dissipating the same
power the nicad pack is taking in. Granted, a charging nicad pack
is endothermic, and a resistor is exothermic...
And the case is tightly sealed. Measurement would be required!

-Chuck Harris

Tom Gardner wrote:
On 11/06/20 16:02, Mark Pilant wrote:
I tried for quite a while to get the "battery fooler" to work *reliably* in
the 1502 and 1503 I have.  I was never successful.
Ditto.

The zener concept isn't too bad, but there is the power dissipation in the enclosed
volume.

I did try the Batteries Plus route and had them make up a replacement pack.
While it looked fine, it wouldn't fit.  The original Tek design used flat
top "C" cells, and pretty much all that is available are button top "C"
cells.  According to the specifications I could find, the "original" flat
top "C" cells were slightly shorter than the button top "C" cells; by the
height of the button.
I have found these acceptable
https://www.batteriesplus.co.uk/acatalog/1.2V_NiCd_Sub_C_Rechargeable_Tagged_Batteries.html

The diameter is slightly too small, but that is easily rectified with some
closed-cell foam.

BTW, I did some checking, and these batteries will last about a month before
needing to be recharged when "sitting" in TDR that has been turned off.
Yes. There is an ~1mA (higher if the chart recorder is present) drain even with the
front panel switch off. If the battery is left in then eventually one or more of the
cells will be damaged by being reverse charged. That's the reason the manual
specified the battery should be charged monthly.

Personally I just leave the battery pack out of the case. If I wanted to keep it in
the case, e.g. for shipping or long-term storage, then I would remove the fuse in the
battery pack.

Chuck Harris

How is a zener dissipating the power necessary to get the
voltage down to 12V any different from a shunt resistor dissipating
the power necessary to get the voltage down to 12V?

Seems to me they are both the same, and both dissipating the same
power the nicad pack is taking in. Granted, a charging nicad pack
is endothermic, and a resistor is exothermic...

-Chuck Harris

Tom Gardner wrote:

On 11/06/20 16:02, Mark Pilant wrote:
I tried for quite a while to get the "battery fooler" to work *reliably* in
the 1502 and 1503 I have.  I was never successful.
Ditto.

The zener concept isn't too bad, but there is the power dissipation in the enclosed
volume.

I did try the Batteries Plus route and had them make up a replacement pack.
While it looked fine, it wouldn't fit.  The original Tek design used flat
top "C" cells, and pretty much all that is available are button top "C"
cells.  According to the specifications I could find, the "original" flat
top "C" cells were slightly shorter than the button top "C" cells; by the
height of the button.
I have found these acceptable
https://www.batteriesplus.co.uk/acatalog/1.2V_NiCd_Sub_C_Rechargeable_Tagged_Batteries.html

The diameter is slightly too small, but that is easily rectified with some
closed-cell foam.

BTW, I did some checking, and these batteries will last about a month before
needing to be recharged when "sitting" in TDR that has been turned off.
Yes. There is an ~1mA (higher if the chart recorder is present) drain even with the
front panel switch off. If the battery is left in then eventually one or more of the
cells will be damaged by being reverse charged. That's the reason the manual
specified the battery should be charged monthly.

Personally I just leave the battery pack out of the case. If I wanted to keep it in
the case, e.g. for shipping or long-term storage, then I would remove the fuse in the
battery pack.

Paul Amaranth

On Thu, Jun 11, 2020 at 11:02:26AM -0400, Mark Pilant wrote:
I made two packs, and have a third 150x battery holder if I want to make
another.

BTW, I did some checking, and these batteries will last about a month before
needing to be recharged when "sitting" in TDR that has been turned off.

73

- Mark N1VQW
I had to fabricate a pack holder for mine. It's just a U shaped piece of
steel with a couple of banana plugs and a separate cover plate on the back.
I think I used sub-C nicads for that.

I keep thinking I want to add a slide switch on the back to disconnect the
batteries when it's not being used. I think that everytime I plug it in
to recharge :-)

Paul

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

Tom Gardner

On 11/06/20 16:02, Mark Pilant wrote:
I tried for quite a while to get the "battery fooler" to work *reliably* in
the 1502 and 1503 I have.  I was never successful.
Ditto.

The zener concept isn't too bad, but there is the power dissipation in the enclosed volume.

I did try the Batteries Plus route and had them make up a replacement pack.
While it looked fine, it wouldn't fit.  The original Tek design used flat
top "C" cells, and pretty much all that is available are button top "C"
cells.  According to the specifications I could find, the "original" flat
top "C" cells were slightly shorter than the button top "C" cells; by the
height of the button.
I have found these acceptable
https://www.batteriesplus.co.uk/acatalog/1.2V_NiCd_Sub_C_Rechargeable_Tagged_Batteries.html

The diameter is slightly too small, but that is easily rectified with some closed-cell foam.

BTW, I did some checking, and these batteries will last about a month before
needing to be recharged when "sitting" in TDR that has been turned off.
Yes. There is an ~1mA (higher if the chart recorder is present) drain even with the front panel switch off. If the battery is left in then eventually one or more of the cells will be damaged by being reverse charged. That's the reason the manual specified the battery should be charged monthly.

Personally I just leave the battery pack out of the case. If I wanted to keep it in the case, e.g. for shipping or long-term storage, then I would remove the fuse in the battery pack.

Mark Pilant

I tried for quite a while to get the "battery fooler" to work *reliably* in
the 1502 and 1503 I have. I was never successful.

I did try the Batteries Plus route and had them make up a replacement pack.
While it looked fine, it wouldn't fit. The original Tek design used flat
top "C" cells, and pretty much all that is available are button top "C"
cells. According to the specifications I could find, the "original" flat
top "C" cells were slightly shorter than the button top "C" cells; by the
height of the button.

While I believe button top batteries could be made to work, because there
appear to be holes for the button, the connections between the cells would
have to be formed, but just a straight across connection.

In the end, I made my own replacement packs using Tenergy Sub-C 2200 mAh
NiCd batteries. The only thing I had to do, as the cells are shorter than
"C" cells, was to sleeve the cells to an appropriate diameter and connect
them all up. I do have an item list and pictures, and can write it up, if
there is interest.

I made two packs, and have a third 150x battery holder if I want to make
another.

BTW, I did some checking, and these batteries will last about a month before
needing to be recharged when "sitting" in TDR that has been turned off.

73

- Mark N1VQW

ken chalfant

Greetings,

FWIW I had Batteries Plus build a new battery array to fit in the battery assembly and It has worked great for several years.

just saying…

Regards,

Ken

On 10Jun, 2020, at 4:06 PM, Chuck Harris <cfharris@erols.com> wrote:

Tektronix tried to be good engineers, and keep the battery
safe from over charge, or under charge.

So, they put a threshold circuit that disables the power supply
if the battery is "dead" (>9.5V), and disables the power supply
if the battery is open circuit, or missing (14V?).

The battery fooler loads down the AC charger built into the 1502
to a voltage that is within the operating range of the battery,
and it adds a capacitor to clean the ripple that the missing
Nicad battery isn't filtering.

In my not so humble opinion, the 200 ohm resistor is a bad idea,
and should be replaced with a nice big heat sunk 12V 10W zener
diode. Or a synthetic zener diode made from a 2N3055 and a smaller
zener diode.

-Chuck Harris

Jeff Kruth via groups.io <http://groups.io/>; wrote:
Hello Folks!

Went to use my 1502 TDR, wouldnt light up. I had built a battery cable for a 12 Volt lead acid external battery, so I charged the 12 V battery up and got it working. I remembered the Battery Fooler mod and looked it up on the Tek site here: 2200 uF cap paralleled with 200 ohm 10 watt resistor. I built one of these in a kaput battery back, plugged it in, and it doesnt work! The little meter is pegged in the green, looks kinda normal. Yes, I got the capacitor polarity right. SO I plugged a power supply into the unit: 12V @ 275 mA or so and the unit operated fine. At 13.5 VDC about 200 mA or so.Am I missing something? The Battery Fooler seemed like a good thing. Should I thinker the cap value? Why the 200 ohm resistor- is this needed to keep the SCR thingy working right? Should the value be increased?Any insight would be appreciated. TIANew info: Tried several caps and resistor values around ther original stated ones: No joy!Regards,Jeff Kruth
BTW Brooke Clarke's 1502 webpage is quite good.

Greg Muir

If you don’t plan on using a battery in the future or simply need to get the unit working on 115V there was sometime in the past a power supply mod where you pulled a transistor off the board and the unit would not recognize a missing battery. But the caveat here is that the mod inhibited the battery over/undercharge circuit so care had to be used by replacing the transistor if a battery was again going to be used.

As for the quality of replacement batteries, I have been using the tabbed Tenergy brand C cells with no problems. Good charge life, charge well and have had packs for years without any failures. The tabs allow you to rebuild the pack with ease.

Greg

Tom Gardner

In my experience the simple "fake batteries" are unreliable. Some work, some of the time, in some 1502s. Twiddling with the values increases the probability of them working.

I prefer to put new NiCd cells in; they cost ~£30/set, plus your time soldering the tags together.

On 10/06/20 22:01, Jeff Kruth via groups.io wrote:
Hello Folks!

Went to use my 1502 TDR, wouldnt light up. I had built a battery cable for a 12 Volt lead acid external battery, so I charged the 12 V battery up and got it working. I remembered the Battery Fooler mod and looked it up on the Tek site here: 2200 uF cap paralleled with 200 ohm 10 watt resistor. I built one of these in a kaput battery back, plugged it in, and it doesnt work! The little meter is pegged in the green, looks kinda normal.  Yes, I got the capacitor polarity right.  SO I plugged a power supply into the unit: 12V @ 275 mA or so and the unit operated fine. At 13.5 VDC about 200 mA or so.Am I missing something? The Battery Fooler seemed like a good thing.  Should I thinker the cap value? Why the 200 ohm resistor- is this needed to keep the SCR thingy working right? Should the value be increased?Any insight would be appreciated. TIANew info: Tried several caps and resistor values around ther original stated ones: No joy!Regards,Jeff Kruth
BTW Brooke Clarke's 1502 webpage is quite good.

Chuck Harris

Tektronix tried to be good engineers, and keep the battery
safe from over charge, or under charge.

So, they put a threshold circuit that disables the power supply
if the battery is "dead" (>9.5V), and disables the power supply
if the battery is open circuit, or missing (14V?).

The battery fooler loads down the AC charger built into the 1502
to a voltage that is within the operating range of the battery,
and it adds a capacitor to clean the ripple that the missing
Nicad battery isn't filtering.

In my not so humble opinion, the 200 ohm resistor is a bad idea,
and should be replaced with a nice big heat sunk 12V 10W zener
diode. Or a synthetic zener diode made from a 2N3055 and a smaller
zener diode.

-Chuck Harris

Jeff Kruth via groups.io wrote:

Hello Folks!

Went to use my 1502 TDR, wouldnt light up. I had built a battery cable for a 12 Volt lead acid external battery, so I charged the 12 V battery up and got it working. I remembered the Battery Fooler mod and looked it up on the Tek site here: 2200 uF cap paralleled with 200 ohm 10 watt resistor. I built one of these in a kaput battery back, plugged it in, and it doesnt work! The little meter is pegged in the green, looks kinda normal.  Yes, I got the capacitor polarity right.  SO I plugged a power supply into the unit: 12V @ 275 mA or so and the unit operated fine. At 13.5 VDC about 200 mA or so.Am I missing something? The Battery Fooler seemed like a good thing.  Should I thinker the cap value? Why the 200 ohm resistor- is this needed to keep the SCR thingy working right? Should the value be increased?Any insight would be appreciated. TIANew info: Tried several caps and resistor values around ther original stated ones: No joy!Regards,Jeff Kruth
BTW Brooke Clarke's 1502 webpage is quite good.

Jeff Kruth

Hello Folks!

Went to use my 1502 TDR, wouldnt light up. I had built a battery cable for a 12 Volt lead acid external battery, so I charged the 12 V battery up and got it working. I remembered the Battery Fooler mod and looked it up on the Tek site here: 2200 uF cap paralleled with 200 ohm 10 watt resistor. I built one of these in a kaput battery back, plugged it in, and it doesnt work! The little meter is pegged in the green, looks kinda normal.  Yes, I got the capacitor polarity right.  SO I plugged a power supply into the unit: 12V @ 275 mA or so and the unit operated fine. At 13.5 VDC about 200 mA or so.Am I missing something? The Battery Fooler seemed like a good thing.  Should I thinker the cap value? Why the 200 ohm resistor- is this needed to keep the SCR thingy working right? Should the value be increased?Any insight would be appreciated. TIANew info: Tried several caps and resistor values around ther original stated ones: No joy!Regards,Jeff Kruth
BTW Brooke Clarke's 1502 webpage is quite good.

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