Re: Hot Snubber

Ross Kudlick

Ed,

A track power “bus” can easily have 2 ends.  If you feed your “bus” near the middle (think of a “T”) the “bus” now has 2 ends.  Putting the booster in the middle of the “bus” run effectively reduces your “bus” length by half.  A 60-foot “bus” becomes 2 30-foot “busses.”  Many consider this as “best practice” when designing a DCC installation.

If you put your booster at the end of the “bus” you would only need one terminator.

Regards,

Ross Kudlick

From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Ed S
Sent: Friday, March 07, 2014 12:21 PM
To: WiringForDCC@...
Subject: RE: [WiringForDCC] Re: Hot Snubber

Here is a little item I had overlooked.  Quoted from http://www.wiringfordcc.com/track_2.htm

"Solution for unterminated bus ends:

The name of this problem suggests the solution - terminate your bus ends. This is simple and inexpensive to do. Just put this "RC network " at each end of your long buses. Yes, you will need two of these circuits for each bus ­ one at each end."

What does he mean  one at each end?  A buss has one end..... or do you need to put one near the booster also.

How many have done that?

Ed S

Re: Hot Snubber

Flash Gordon

Here is a little item I had overlooked.  Quoted from http://www.wiringfordcc.com/track_2.htm

"Solution for unterminated bus ends:

The name of this problem suggests the solution - terminate your bus ends. This is simple and inexpensive to do. Just put this "RC network " at each end of your long buses. Yes, you will need two of these circuits for each bus ­ one at each end."

What does he mean  one at each end?  A buss has one end..... or do you need to put one near the booster also.

How many have done that?

Ed S

Re: Hot Snubber

Vollrath, Don <dvollrath@...>

The dissipation heat in the resistor for a DCC bus snubber will be in direct proportion to the value of the capacitor. The 100-220 ohms value of the resistor makes little difference.

0.1   microfarad is the ideal value. 0.47 uF is too big and will cause the resistor to run very hot. 0.01 uF is too small and not add enough ‘noise’ suppression to help the situation. Any type of non-polarized capacitor, except for tantalum, will be sufficient. 0.1 uF, 50V ceramic caps are adequate, small and inexpensive.

Yeah… RShack first substituted R/C toys then cell phones do-dads for audio amps, speakers and other useful electronic parts in many stores. That has shown up on the yearly spreadsheets as a poor business decision.

DonV

From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of asychis@...
Sent: Friday, March 07, 2014 8:49 AM
To: WiringForDCC@...
Subject: [WiringForDCC] Re: Hot Snubber

A couple of questions:

I take it that a "snubber" is the same as a buss terminator?

If you are using snubbers to terminate all your busses, do they all need to use the same value for the resistor and capacitor?  It looks like the recommended values are 100 ohms and .1 mfd for the resistor and capacitor, respectively.

What are the consequences of changing these values?  If I had one snubber with a 100 ohm resistor and .1 mfd cap and another with a 100 ohm resistor and a .47 mfd cap, would there be problems?

I am starting to terminate all our busses on the club layout and want to make sure I get it right.  I thought I could easily pick up the components at Radio Shack, but at least in Amarillo they carry few components these days.  Mainly bits and pieces.  In all the Radio Shack stores in Amarillo I found six ceramic and four mylar .1 mfd capacitors.

That leads to a final question, is there any problem mixing ceramic, mylar and other types of non-electrolytic caps?

Thanks!

Jerry Michels

Re: Hot Snubber

jazzmanlj

Measure with the power off. Use a simple ohm meter across the cap. It should read infinite resistance.

Never use an ohm meter on powered equipment.

Len

Re: Hot Snubber

asychis@...

A couple of questions:

I take it that a "snubber" is the same as a buss terminator?

If you are using snubbers to terminate all your busses, do they all need to use the same value for the resistor and capacitor?  It looks like the recommended values are 100 ohms and .1 mfd for the resistor and capacitor, respectively.

What are the consequences of changing these values?  If I had one snubber with a 100 ohm resistor and .1 mfd cap and another with a 100 ohm resistor and a .47 mfd cap, would there be problems?

I am starting to terminate all our busses on the club layout and want to make sure I get it right.  I thought I could easily pick up the components at Radio Shack, but at least in Amarillo they carry few components these days.  Mainly bits and pieces.  In all the Radio Shack stores in Amarillo I found six ceramic and four mylar .1 mfd capacitors.

That leads to a final question, is there any problem mixing ceramic, mylar and other types of non-electrolytic caps?

Thanks!

Jerry Michels

Re: Hot Snubber

Vollrath, Don <dvollrath@...>

If the snubber is still connected to the DCC bus there may be other loads seen by an ohmmeter at the snubber, so the cap may not measure infinite ohms. An alternate technique would be to short the DCC bus with a jumper (so we know it measures 0 ohms) then use the ohmmeter to measure the cap. You should see 100 ohms of the resistor, nothing less.

OR

With DCC power on, use an AC voltmeter to measure voltage across the cap. It should be almost the same as measuring across the bus or track. Or measure the AC voltage across the resistor, it should be almost zero.

DonV

From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of redking56@...
Sent: Friday, March 07, 2014 7:11 AM
To: WiringForDCC@...
Subject: RE: [WiringForDCC] Hot Snubber

Can I measure with the snubber in place with the power off or do I need to remove the snubber from the bus wires?

Rich

---In WiringForDCC@..., <dvollrath@...> wrote :

The capacitor may be shorted. In that case the 100 ohm resistor may become very hot as it will be dissipating almost 2 watts. With the snubber disconnected, try measuring the resistance from terminal to terminal, or just across the capacitor, with an ohmmeter. It should measure infinite ohms or open circuit. If not, it needs to be replaced.

DonV

From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Mark Gurries
Sent: Thursday, March 06, 2014 3:34 PM
To: WiringForDCC@...
Subject: Re: [WiringForDCC] Hot Snubber

Snubber will have warm resistors.  The resistor will only get warm when DCC power is present.

If one seem hotter than the others, check the resistor and the capacitor value of the warmer Snubber compared to the others.

I suspect the resistor may be a lower values or the capacitor may be a higher value.

On Mar 6, 2014, at 1:03 PM, <redking56@...> <redking56@...> wrote:

I was working under my layout today and noticed  that a stubber is hot to the touch.  The other snubbers are cool to the touch.  What could be the problem with the hot stubber.

Rich

Best Regards,

Mark Gurries

Electrical Engineer

DCC Website & NMRA DCC Clinics: www.markgurries.com

Re: Hot Snubber

redking56@...

Can I measure with the snubber in place with the power off or do I need to remove the snubber from the bus wires?

Rich

---In WiringForDCC@..., <dvollrath@...> wrote :

The capacitor may be shorted. In that case the 100 ohm resistor may become very hot as it will be dissipating almost 2 watts. With the snubber disconnected, try measuring the resistance from terminal to terminal, or just across the capacitor, with an ohmmeter. It should measure infinite ohms or open circuit. If not, it needs to be replaced.

DonV

From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Mark Gurries
Sent: Thursday, March 06, 2014 3:34 PM
To: WiringForDCC@...
Subject: Re: [WiringForDCC] Hot Snubber

Snubber will have warm resistors.  The resistor will only get warm when DCC power is present.

If one seem hotter than the others, check the resistor and the capacitor value of the warmer Snubber compared to the others.

I suspect the resistor may be a lower values or the capacitor may be a higher value.

On Mar 6, 2014, at 1:03 PM, <redking56@...> <redking56@...> wrote:

I was working under my layout today and noticed  that a stubber is hot to the touch.  The other snubbers are cool to the touch.  What could be the problem with the hot stubber.

Rich

Best Regards,

Mark Gurries

Electrical Engineer

DCC Website & NMRA DCC Clinics: www.markgurries.com

Re: Hot Snubber

redking56@...

Len,

I am going to go down to the layout in a few minuted and do just that.  I was surprised yesterday to discover that hot snubber.  Never noticed that before with any of the snubbers.

Rich

Re: Hot Snubber

jazzmanlj

Rich,

You should try to determine why it is running so hot! I'm assuming it's the resistor running hot. What are the values and power ratings? Have you measured the cap as to possible short as Don suggested?

Len

Re: Hot Snubber

redking56@...

This particular snubber is hot enough that if you grasp it in your fingers and hold it for more than a second, you will burn your fingers.  It is very hot to the touch.  I am going to replace it.

Rich

If the component values are the same for all snubbers then the voltage spikes are much greater in that area. How hot is 'hot to the touch'? Rule of thumb is if you can hold the part continuous it's less than 55C and that is acceptable. If you're uncomfortable with the heat go with a higher power resistor. Do not use wirewound resistors!

Re: Hot Snubber

jazzmanlj

If the component values are the same for all snubbers then the voltage spikes are much greater in that area. How hot is 'hot to the touch'? Rule of thumb is if you can hold the part continuous it's less than 55C and that is acceptable. If you're uncomfortable with the heat go with a higher power resistor. Do not use wirewound resistors!

Re: Hot Snubber

Vollrath, Don <dvollrath@...>

The capacitor may be shorted. In that case the 100 ohm resistor may become very hot as it will be dissipating almost 2 watts. With the snubber disconnected, try measuring the resistance from terminal to terminal, or just across the capacitor, with an ohmmeter. It should measure infinite ohms or open circuit. If not, it needs to be replaced.

DonV

From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Mark Gurries
Sent: Thursday, March 06, 2014 3:34 PM
To: WiringForDCC@...
Subject: Re: [WiringForDCC] Hot Snubber

Snubber will have warm resistors.  The resistor will only get warm when DCC power is present.

If one seem hotter than the others, check the resistor and the capacitor value of the warmer Snubber compared to the others.

I suspect the resistor may be a lower values or the capacitor may be a higher value.

On Mar 6, 2014, at 1:03 PM, <redking56@...> <redking56@...> wrote:

I was working under my layout today and noticed  that a stubber is hot to the touch.  The other snubbers are cool to the touch.  What could be the problem with the hot stubber.

Rich

Best Regards,

Mark Gurries

Electrical Engineer

DCC Website & NMRA DCC Clinics: www.markgurries.com

Re: Hot Snubber

Mark Gurries

Snubber will have warm resistors.  The resistor will only get warm when DCC power is present.

If one seem hotter than the others, check the resistor and the capacitor value of the warmer Snubber compared to the others.

I suspect the resistor may be a lower values or the capacitor may be a higher value.

On Mar 6, 2014, at 1:03 PM, <redking56@...> <redking56@...> wrote:

I was working under my layout today and noticed  that a stubber is hot to the touch.  The other snubbers are cool to the touch.  What could be the problem with the hot stubber.

Rich

Best Regards,

Mark Gurries
Electrical Engineer
DCC Website & NMRA DCC Clinics: www.markgurries.com

Hot Snubber

redking56@...

I was working under my layout today and noticed  that a stubber is hot to the touch.  The other snubbers are cool to the touch.  What could be the problem with the hot stubber.

Rich

Re: Wiring for Current Sensing detection.

jazzmanlj

This is basic magnet coupling and insulation is a must, as an any transformer. Insulation has no effect on the magnetic fields created by the main wire through the current transformer. One wire through the center of a toroid is one turn.

If insulation is removed and another turn added there could be a possibility of shorted turns and all bets are off.

Re: Wiring for Current Sensing detection.

johnwv47

Thanks Don and Max for your responses. I haven’t decided on what equipment to use yet but Max’ suggestion allows for a coil to be added later so that’s a good tip. Thanks, JV.

Re: Wiring for Current Sensing detection.

Vollrath, Don <dvollrath@...>

Don't worry about the length of the block. Just provide two or three track droppers fed by that same sub bus wire so that all the current is being measured.

DonV

On Mar 5, 2014, at 5:55 PM, "John Vos" <johnandrobyn@...<mailto:johnandrobyn@...>> wrote:

Thanks for the reply, Don. I was concerned about feeding a block some 14 feet long through one wire . I understand that the feeder should also be wrapped through the hole. Should the insulation be stripped away for that? Thanks.

Re: DCC

Vollrath, Don <dvollrath@...>

Yes the decoder output to the motor is an H bridge. That is only practical way to get PWM voltage control with reversing capability.

DonV

Don,

Are you implying the decoder has an H-bridge for the motor drive? The booster is an H but I've not yet seen any schematics of a decoder. Can you elaborate?

Re: DCC

jazzmanlj

Don,

Are you implying the decoder has an H-bridge for the motor drive? The booster is an H but I've not yet seen any schematics of a decoder. Can you elaborate?

Re: DCC

jazzmanlj

Thanks Don,

CT's are very good in control but need tuning as to burden resistors and filtering, More schematics to procure and study!

I fully retract my statement as to the motor inductance. Didn't think it clear, but I would model a loco or any other device connected to the track as a black box with some sort of RLC network.