Circuit Breakers & Boosters not resetting after a short with sound equipped locos.

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Mark Gurries’s technical explanation.

Rex Beistle PM42 solution that I have used in the PM42 diagram.


Operators in the U.S and here (Australia) have had trouble with circuit breakers and boosters not resetting after there has been a short circuit (running against a point or turnout etc) on the layout, when there is a few sound locos in the same power district controlled by a circuit breaker or booster.


I had this problem when I was building a DCC demonstration module and I fitted an EB3 from NCE, a 3 channel electronic circuit breaker. I searched the DCC Yahoo Groups and at Tony’s Train Exchange, I found a statement that, when there are Soundtraxx equipped sound locos on the layout, that there were problems with the Power Shields resetting. Power Shields and EB3 are similar.


I resolved my problem with the EB3 after getting advice from Mark Gurries on the Yahoo NCE group, to fit a lamp in parallel with the circuit breaker, as shown in the photo and diagram below.


Why? - The circuit breaker cannot differentiate between a short circuit and the larger “inrush current” requirements of few sound locos. The more sound locos in a zone, the more current is required in this “reset 2 seconds”. Increasing the trip current jumpers on the EB3 only marginally improved the reset operation. Adjustment of the trip response time more than the default 1/10th second may cause the booster to trip and not the EB3, when there is a short.


Using a 5 Watt lamp, Hella Part No W125, similar to the 168 available in the U.S, I found that I could have 6 sound equipped locos in the same power district and the EB3 reset automatically. If locos were idling with sound on, then I had to increase it to 10 watts. See table below and Auto Lamps in DCC for the wattage of the lamps I have used. Experimenting with lamp wattage until particular loco density requirements have been fulfilled, will enable the EB3 to reset normally.


Tests - EB3 reset times after the short is removed

Without bypass lamp.

1 sound loco – 2 seconds

2 sound locos – 5 to 40 seconds

3 sound locos – Would not reset (still not reset after 5 minutes).


With a 12 volt 5 watt Hella W125 or 168 bypass lamp.

3 sound locos – 2 seconds

4 sound locos – 2 seconds.

5 sound locos – 2 seconds.

6 sound locos with idle sounds - 8 to 40 seconds.


Use a 10 watt 97 lamp for 5 or more locos in the same power district.


The use of 1156s for this “work around” will give a very bright visual indication with a current of approximately 2.0 amps flowing through the short. Unless you have more than 10 sound locos in the same power district, no need to use an 1156. Note: I use 1156s for short circuit and power district management on my layout. There will be no problems using these lamps, IF the short is rectified immediately and not left unattended. See my article on Using the 1156s.


Note: I have spoken to Jim Scorse and he has tested the EB3 with a 168 wedge lamp and is happy with using this lamp to allow a reset of the EB3s. Remember this problem does not happen on all layouts.



Fitting the parallel lamp fix with each circuit breaker channel, as shown above, has provided correct operation of the circuit breaker, but will allow a current of .35 amps for a “168” lamp to flow, when there is a short, thus the EB3 does not disconnect the power to that power district (layout) .


This lamp effectively provides a parallel path for the current. With the EB3 under normal operation, negligible current flows through the lamp due to the higher resistance parallel path. When there is a short circuit and the EB3 trips, now there is current flowing to the short as determined by the wattage of the lamp, the higher the wattage, the more current. When the short is removed and the EB3 is attempting to reset (circuit breaker is determining if there still is a short for 2 seconds) the lamp current provides the major portion of the initial large inrush current for all the sound decoders, so when the EB3 “closes”, it supplies the remainder of the inrush current. This EB3 sensed inrush current is less than the “trip current” settings of the EB3. So now the operation of the EB3 is automatic.

Figure 1


Some modellers might say, why not just use 1156s and remove the EB3 or other circuit breakers (I do on my layout, I only use 1156s). Using 1156s, do create voltage drops and thus a maximum of about 3 to 4 locos including sound, operating in one power district. Using the EB3 and Power Shields with the 168 parallel lamp, gives the best of both worlds – operating without a voltage drop (limit on locos) and allows automatic resetting.  


A benefit of using this “parallel lamp fix” for ALL circuit breaker installations is that the lamp can be located remotely, say 20 or more feet away from the EB3. The lamp if located in a suitable line side building becomes a very effective visual warning of a short. This visual warning is a great way to indicate whether the train operator has a short (lower photo), instead of dirty track (upper photo) when his train stops.


Not everyone has the problem Different layouts have exhibited varying results for sound loco circuit breaker reset operation, so fit either circuit breaker (EB3 or Power Shield) and see what happens. If everything operates without any problems with the circuit breaker resetting, don’t do anything.


NCE’s EB3 intermittent or no operation.  A few modellers have reported that their EB3s did not work at all when installed or had intermittent operation.

The problem is that one or more of the 2 term terminal strips, (4 off) have dry joint or bad connections to the circuit board. Inspect and re-solder these joints and check for operation.


Power Shields from TTX. The Power Shields have a similar problem with sound resets and this is rectified the same way, with a parallel lamp. Connect the lamp from DCC 2 (Input) and Rail 2 (Output) connections as shown below. Only one lamp is required. Use the lowest wattage lamp possible to get the results you need. I have not tried this “fix” on the Power Shields. A few modellers have told me the 1156s work on the Power Shields.


This interim fix, will enable layouts where circuit breakers have been fitted and operating with sound locos, to operate correctly until manufacturers (decoder, circuit breakers and boosters) have modified their products, to take into consideration the higher inrush current requirements. There is no problem with circuit breakers with non sound locos.


This problem happened with me with Soundtraxx equipped locos and BLI operators in the U.S. were having the same problems. Some modellers have implemented the fix and are operating happily, while others are not adding anything to their systems to correct what they feel is a QSI or Soundtraxx problem.


The reason that this problem surfaced now, was that when the circuit breakers and booster were designed, the NMRA Standards never stated an “Inrush Current” value. With non sound locos there were no problems and everybody was happy.


With the increasing popularity of sound locos ever since Broadway Limited released ready to run locos with sound, this “Inrush” has appeared on more and more layouts and users are reporting the inability of the circuit breaker or booster, to reset without removing power to the layout (or booster).


With later releases of sound decoders, circuit breakers and boosters, hopefully this problem will be resolved by manufacturers improving their circuits for charging capacitors and sensing currents for shorts/inrush. Only time will tell if this happens.


If a DCC system that only has boosters and no circuit breakers, then you cannot add a parallel lamp to the booster. Circuit breakers will have to be introduced to eliminate the booster from cutting out. If there are problems with the circuit breakers then, then parallel lamp can be fitted.


Power Shields from Tony’s Train Exchange are advertised now to allow more sound locos to be in the same power district before the circuit breakers exhibits problems with resets after a short.


Tony’s Power Shield Four:


PS-4s are two PS2 assembled onto one board.

The booster inputs to the PS-2, if fed from one booster are joined together shown with the green lines.


The lamps for each section shown as Lamp 1 through Lamp 4 are connected from “DCC 2” to each “Rail 2”. This gives a parallel path for the current through the circuit breaker section for each of these sections.


As with the EB3, experimenting with lamp wattage until the particular loco density requirements have been fulfilled that will allow the Power Shield circuit breaker channel to reset automatically. Start with a 168. If the Power shield does not reset with the amount of sound locos you have in one zone, then increase the lamp wattage to a 1141 (18 watt) or an 1156 (27 watt). I don’t have any Power Shields but others have told me the 1156 works great. See Auto Lamps in DCC for auto lamps in DCC and the numbers. If you don’t want to experiment just use the 1156.




































Photo of Tony’s Shown below is a Power Shield Four (PS-4) setup with “barrier” terminal strips courtesy of Vince Vargus,

(16 Apr 06) showing how two PS-2 are assembled together to form one PS-4. Thank you Vince.


Vince has shown his wiring method of terminating the PS-4 using barrier strip terminal boards.


On the left is the terminal board to connect the DCC from the booster.


On the right is the terminal board to the 4 power districts.


Note Each PS-2 is treated separately. If he feed for the PS-4 is from one booster, then the two pairs of black and red wires on the left are linked together. 


For each circuit breaker section, the “sound reset lamp fix” lamps would be connected between one black wire on the “DCC 2 to the other black wire on the right “Rail 2”. Two lamps are connected to each of the black wires on the left, the DCC input.









Digitrax PM42s and PM4s:


Rex Beistle has said that the PM42s and the PM4s have the same problem and can be fixed by the same parallel lamp fix. Thanks Rex.


The PM42 &PM4 require 2 lamps per power zone feeders, thus 1156 lamps (27 watts) will be required and since both of these lamps will be in SERIES with the load (short), they will reduce the short current to around 1 Amp and will not glow at all, no visual warning (bummer!!!!). I don’t have a PM42, so I cannot experiment here.


For other system users, you must have a Digitrax system to program the PM42s and PM4s, so this feature makes them unsuitable for power management if you have other than a Digitrax DCC system.



Note: The PM4s can be upgraded to PM42s with a kit from Digitrax due to their slow response time and causing the booster to trip instead of the PM4.



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Some previous history on the Circuit Breaker problem. Some of the early emails, are included below, about my initial problem and Mark Gurries technical explanation of the problem with possible solutions. Makes for very interesting reading and how some things get past the early setting of Standards by the NMRA. We, including manufacturers, are all learning about DCC. Thanks a lot Mark.


Hi All


Back in July last year while building a demonstration DCC module I came across this problem, more than one Soundtraxx equipped loco in the same power district and my NCE EB3 circuit breaker would not reset.


I looked on all the lists and found on the Digitrax list that some modellers were having this problem. I posted on the NCE, Soundtraxx and QSI list my test results and asked for some help.


I looked up Tony's site and under his auto reversers, that since has been updated, a statement about Sound Considerations at:

and it said that the reverser had problems resetting with Soundtraxx locos in the same power district.


Mark Gurries on the NCE group suggested I wire a 12 volt lamp in parallel with my NCE EB3 and I experimented with different wattage lamps and was able to get the results I wanted with 5 - 10 watt lamps.


Tony's Power Shields, Digitrax's PM42s and PM4s as well as the NCE EB3 were having the problems along with some power boosters. I helped a couple of U.S. modellers who had fitted TTX Power Shields, get their layouts running properly, but they were happy to fit the "fix" if it meant be able to have normal trouble free sound loco operation, One was a Digitrax user and the other was an NCE user.


Many modellers with BLIs were very disappointed with the booster inability to reset after a short. I have only Soundtraxx units and I have the problem.


I had the same problem when I connected my EB3 directly to my Command station/booster track outputs and only one piece of track on my work bench, so in my case nothing to do with my layout and wiring.


I am on a few groups and some people have reported it while others have said they have many BLIs and don't have any problems. About August September last year, many modellers on the QSI group voiced their frustration about this problem and I am sure that is all DCC system are suffering the same problem.


The problem is that when a booster or circuit breaker tries to reset when there is a short, it connects back on line and if the high current that a short creates, is still present, it disconnects again. This process is repeated every few seconds until the booster/circuit breaker does not see a short. Now the problem is that when there is a short with sound locos, their onboard capacitors discharge and when the booster/circuit breaker is trying to reset after the short has been removed, this "Inrush Current" to charge the capacitors is high and depending on how many sound locos are in the same power district will determine on how high a current and for how long. If the current values are higher than the criteria of a sensed short, then the booster sees this as a short. It cannot tell the difference between a short and a high inrush current sound reset with a few sound locos.


For those that want a more technical description and possible solutions, I have included Mark Gurries's reply on the NCE group about the problem with Sound locos and booster/circuit breaker resets.


Hope this helps.




Mark Gurries technical explanation.                                                      Top of page


-----Original Message-----From: Mark Gurries [] Sent 28 July 2004

Subject: Re: [NCE-DCC] EB3 too slow to reset after short


Sound equipped locomotives have presented challenges to DCC that were not anticipated when the NMRA specification were written.  The problem is the amount of capacitance that needs to be charged up to allow the sound electronics to function reliably with various types of DC power that is NOT pure DC. The capacitor charge current is a huge spike involving amp levels that far exceed the current capability of the both boosters and Circuit breakers.  But it does not take long to charge. But every  time you add another sound equipped engine, the problem grows in size to a point it will become a major problem.


Prior to BLI, sound equipped locomotives were few and quite a show item initially since it involved a lot a work to install a sound system. (But what head turners the sound units were!)  Anyway, the problem existed but showed up at more of an annoyance level issue.


When BLI came on the scene, things changed quickly.  Engines with sound became "Ready To Run" along with good quality construction allowed people to acquire more sound equipped engine faster than ever.  Today most BLI customer come back for more and having many sound equipped engines on the layout has now become common place.  Correspondingly, the problem is has now become a BIG issue.


Here is how the problem happens.


Electronic based Circuit breakers use Current Level and Time Duration to determined the difference between a normal momentary short circuit (normal stuff rolling down the track) versus a real short (caused by a

derailment) where the short current can be sustained indefinitely.


Sound decoders have BIG capacitors in them that are used to store power to keep the sound going un-interrupted as the engine roles down the track make less than perfect electrical power pickup at all times.  These capacitors must be charged up BEFORE the sound system will work.  When they are first charged up, they look like a short to booster or circuit breaker.  The short circuit current level fades quickly with time for it only momentary.  The current goes to zero when the cap is fully charged up.


If the capacitor current fades fast enough below the short circuit trip level before the circuit break decides it is time to kill power, then everything works like you expect.  No problem.  If the current trip level is lowered or reduced, then the exact same capacitor current will not fade fast enough to clear and the circuit breaker will trip. 


Adding more sound equipped locomotives is the same as adding more capacitors in parallel.  Depending on your electronic circuit breakers setting and the peak current capability of your booster, people will get various degrees of success and failure with combinations of locomotives. The layout wiring also plays a part here too.  So there are lot of variables involved on the layout side.  What fails to function on layout A may work just fine on layout B.


Your light bulb solution works because it adds resistance in series with the engines limiting the peak current.  The down side with the light bulb is that if you have a lot of engines on the same section, the track voltage will drop a lot as the light bulb starts to glow.  The engines will not run well.



Technical Discussion and discussion of possible solution at the Manufacture's end...


The amount of capacitance to put into a sound decoder will have a minimum and maximum requirement.


The minimum capacitance dictated for the circuit are typically concerns that are covered by the datasheet of the parts involved or an engineers experience with the circuits involved.  But all of these specifications assume the power is clean and un-interrupted (Pure DC).  In this case, we put the sound system on wheels with intermittent contact which changes the capacitance requirement to work beyond the minimum.  The maximum, however, is determined by the decoder sound system designer through actual real world testing to handle the intermittent contact situation.  Large capacitance capacitors will store more energy and keep the sound going through longer durations of power dropouts or dirtier track so to speak. Unfortunately there is no standard for "intermittent contact" in terms of time and strength.  Another factor determining capacitor size is the requirement to have the sound unit work with old DC power.  Many DC power packs have pulse power or less than pure DC power that was targeted specifically for motor control and not to run electronics.  A BIG capacitor is again needed to filter out all those pulses to allow generation of enough pure DC to run the electronics.  So the solution is all over the map depending on who did the design and what the design goals are.  At the same time cost and space issue may become a factor in deciding what to do.


Soundtraxx discovered with the DSD that there was not enough capacitance to make all the customers happy.  Yet the size of the decoder was a big concern since not every would have the space to fit a large capacitor if it was factory installed.  Although they never updated the DSD design (now that Tsunami DSD is to replace it), the did address it with the DSX by allowing one to optionally add extra capacitance.  There is a technical note about how to do just this on the Soundtraxx website. Since decoder size is a Soundtraxx feature, having enough capacitance is a tough issue to address. I think the DSX approach is good idea that they should keep in the Tsunami product when it comes out.



QSI, which does the sound for BLI and Lionel and perhaps others, has the luxury of making decoders that are specifically design to fit in space provided by the locomotive from the day the locomotive design was started. Since the sound unit is guaranteed to fit, size is less of an issue and unlike Soundtraxx, can use less expensive and bulkier components.  Their boards reflect just that design and thinking.  They are huge compared to Soundtraxx boards.


From an electrical standpoint, there are two parameters that determine the effective short circuit current level and durations.


1) The circuit impedance.  Using Ohms law, V = I x R and re-writing it to I = V/R we can see that there is a direct relationship between the current, track voltage and circuit resistance.  If the resistance goes down, the current goes up.  The resistance is all the resistance in the complete loop of current flow from the booster to the track to the sound board through the cap back out all the way back to the booster. Typically this resistance is less than 2 ohms and typical track voltage is 14.5V.  So the maximum current is really limited by what the booster will provide.  So clearly every time the cap charges up, we WILL hit the booster current limit. 


Part of that resistance is the resistance inside the cap which is called ESR or Equivalent Series Resistance.  Its resistance value can be high relative to the layout wiring resistance.  High performance caps will have low ESR and cheap caps will have high ESR.    Low ESR will result in High peak Current Flow into the cap.  High ESR will reduce or limit the peak current to a lower value.  So the choice of cap can also effect the peak current value.


2) The capacitance value of the capacitor(s).  Simply put, the more capacitance you have, the more energy you can store. Its a bigger rechargeable battery so to speak! That also means if the current available to charge up the cap is limited, the longer in time it will take to charge up to full.


So the worse thing to have is a low ESR cap with high capacitance.  It will draw high current and sustain that high current for a long time. Just what the Circuit Breaker is looking for to shutdown.  For a given size, cheaper caps will have higher ESR and Store less energy.   So there are cost versus Size versus performance tradeoffs that must be made.  The total capacitor solution will then vary with the application requirements.


The thing that bothers me is that there is a simple solution the high current cap charge inrush current.  First install the minimum capacitance needed by the parts on the board.  Then add the extra big capacitance for intermittent power holdup in parallel with the small cap but with a circuit change.  Put a combination diode + resistor in series with the big cap with the diode in parallel with the resistor.  The Resistor will limit the peak current or power to a safe level when charging up that is well below any trip limit.  The diode allows the cap to bypass the current limiting resistor and provide full power to keep the sound unit running when power is momentarily lost.  It cheap, small and simple to do.  I hope the Soundtraxx Tsunami has that or fixes the problem some other way.


If the NMRA DCC body was to do something, it would be to define a inrush current profile that all booster and circuit breakers must pass and to recommend the circuit in question be designed to minimize the inrush current below this inrush current profile as best as possible.


Hope this helps.


Mark Gurries




Hi All.


Since I posted the below message about slow response times of EB3  I have done some experiments. With CV 49 set at 10 (100 mSecs), system works ok only if one sound equipped loco is in power zone, but with two locos in same zone, double headed or second in a siding but still powered, the EB3 does not reset within a reasonable time.

Changing CV 49 to 11 to 14 still no good. With CV 49 set to 15 (150 mSecs) when there is a short in the zone then all three status lights start flashing and after a few seconds, command station trips. This is not a desirable result.


If I increase current trip limit to 3 Amps then sometimes ok. Put 3 sound equipped locos in zone - no good, if  I increase to trip limit to 4 Amps still won't reset in reasonable time of what I would expect say within 5 - 10 seconds. See results below.


These are my test results. My sound locos in all tests, all have Soundtraxx DSD100LCs. I don't have any BLI locos. I have wired up EB3 off the layout and on my bench with no other track connected and away from any other track wiring and using only one channel at a time.


Trip current 2 amps

1 sound loco = OK

2 sound locos = reset sometimes after at least 1 minute


Trip current 3 amps

2 sound locos = reset 5 to 40 secs and 50% greater than 1 minute


Trip current 4 amps

2 sound locos =  resets after 5 - 10 seconds most of the time 3 sound locos = never resets in less than a minute


Above tests done on circuit breakers 1 & 2 and CV 49 and 50 set at 10(100msecs)


These results are not good since I have 9 sound equipped locos and if I am running 2 consisted sound equipped locos and I am in a zone where there is one other sound equipped loco parked, then EB3 will not reset in less than a minute and that is only when I have set current trip to 4 amps. If I am running 1 sound loco and have a short in a zone where there are 2 sound locos parked like in a yard, the EB3 will not reset in less than a minute.


If this is normal operation of EB3 then I will go back to running with automotive tail lights as power district protection control, but I think the EB3 should work better than this. I reviewed all NCE Yahoo Group messages and there has been no reported problems with EB3 except one with "EB3 Jitters".


With above results I had divided my layout into 3 zones with EB3 and even if I had 6 zones (2 EB3s), I would have problems.


Today I searched on Tony's Trains  and found this about his Power Shield Circuit Breakers and under "Soundtraxx Considerations" it says you cannot expect the Power Shield to reset with 3 or more Soundtraxx locos in one zone. These are the results I am getting with my EB3 and that is only when current trip is set to 4 amps.


So it seems that those of us that run sound equipped locos, then we can only have at best 2 Soundtraxx equipped locos in one zone for Electronic Circuit breakers to work. This can be with single sound loco operating train and one parked in siding or anywhere else. What happens at a yard or roundhouse? I guess I will have to go back to either light globes or as some have been doing when locos not used are parked and track turned OFF, sounds like going back to crude "block control". I thought this is why I am using DCC to get away from control panels.


I wonder what all of you with sound locos have done when operating in power zones protected by EB3 or Power Shields to overcome this problem.


Please let me know.




----- Original Message ----- From: "Marcus Ammann"  To: Sent: Monday, July 19, 2004 4:58 PM

Subject: [NCE-DCC] EB3 too slow to reset after short



Hi All


Just wired in an EB3 for power district protection instead of using 12V 18W automotive tail lamp and the time for the EB3 to reset after tripping out for a short (status light flashing) can be 5 secs to 1 minute and sometimes longer. Have set CV 49, 50 and 51 to other than 100 m secs and no difference. If set to 300 m secs then Booster switches out. This would be normal. Have tried on 2 of the 3 circuit breakers. Trouble seems to be with a sound loco with a DSD100LC decoder. Seems to work okay with a non sound loco. If this is normal, I'm disappointed ‘cause I running a few sound locos.


Am building a demonstration module for a clinic I'm doing on DCC to show how good DCC works.


Has anyone experienced this or do I have a faulty unit. May go back to tail lights, everything worked ok but I thought I should go the EB3 way.






Rex Beistle’s reply


Below is a message from Rex Beistle replying to Craig’s problems that he was having with a PM42 not resetting with his  Walthers lighted passenger coaches. This is the same inrush current problem that is happening with sound locos.



--- In, "Craig" <craigb@p...> wrote:


Any start up limiting needs work every time the power is turned on or if there is a momentary short at a turnout, causing the PM42 to trip, the problem starts all over. Once the PM42 trips, it waits  and then turns the power back on, when this cycle starts, it just keeps "clicking" off and on.


Perhaps a simple addition to the PM42 could help. I am not a great proponent of the light bulb as a do all/cure all, but maybe in this case it could be used to advantage.

Lets presume that you are using section 1 of the PM42. Pins 4&D are the rail A input and pin E is the track output A. Likewise pins 7&H are the rail B input and pin F is the track output B. The input connects to the common terminal of a relay and the track output connects to a normally closed terminal on the same relay. If there is no short, the relay is closed and the input is connected to the output. In case of a short (or power on inrush current problem) the relay is energized (picked) and the current from the booster is interrupted.

If a lamp is connected from pins 4&D to pin E, and another lamp from pins 7&H to pin F, then the lamps will be in the circuit during a short. The lamps may pass enough current to bring the lighted cars (or Soundtraxx decoder) up to some intermediate voltage level while the PM42 is timing out to retry. When the time out occurs, the lamps would be taken out of the circuit and full voltage would pass through the relay on the PM42. Some fiddling with the lamp selection may be necessary - one might start with the industry number 1156 or something similar rated at 12 volts and perhaps a couple amperes. I have had cold lamps cause DB200 boosters to shut down when placed directly across the output terminals. Putting lamps across the PM42 would put them in series with the layout and would not be the same as putting them across the booster output.

Initial power on would result in an overload and the PM42 would say 'short' putting the lamps in series with the booster output. Hopefully the lamps would pass enough current to 'charge up' the layout power district and equipment so that when the PM42 times out and retries all will be OK. This little scheme would come into play each time the PM42 said "short." Remember to keep the lamps away from things that cannot handle the heat! I do not want to read about fires or other damages or any kind of injury.

A cheap and dirty 'soft start' that just might work.

Give it a try, what you have is not meeting your needs.

Rex Beistle
, Colorado

NMRA 17832
The Denver HO Model Railroad Club, located at
The Colorado Railroad Museum in Golden, Colorado
visit us at
visit the NMRA at


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