Shorts, Power Districts, and the 1156 - Characteristics and Tests.

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Test of the 1156 showing current & resistance readings.


Locos slow up using the 1156


See Joe Fugates video about using 1156s for short management.



Power Districts


When there is a short, typically caused by an operator running “against” an incorrectly set Point or Turnout, the power to the whole layout, shuts down. While this is satisfactory for a single operator, it is very annoying when there are a few operators.


This annoying total interruption can be eliminated by dividing your layout into Power Districts, achieved by using:


More Boosters – These are expensive and not really required on layout operating approximately 10 or so trains.

A Circuit Breaker – Much cheaper (AS20 to A$25) per section, making them a much cheaper alternative to Boosters.

An 1156 automotive lamp.


The $2, 1156 automotive 12 volt 32 candle power (27 watt) brake lamps that are not new to model railroads, can be used to restrict the current to 2.0 amps when there is a short. The booster does not cut out. It supplies the current to the 2.0 amp short power district and all other power districts, thus operation on the other power districts is not affected. The lamp does not remove power to the short.


See Joe Fugates video about using 1156s for short management.


Shorts in DCC.


There is a lot of confusion here. The short that normally happens (99.9%), that trips the booster or circuit breaker or that illuminates the 1156, is a short at the rails. These include:


1.   An operator running against an incorrectly set of points or turnout.

2.   The back of a wheel contacting the closure rail on a turnout.

3.   Out of gauge wheel sets going through turnouts.

4.   Bad track alignment at turnouts.

5.   A derailment.


Some of the above fault conditions can be reduced by making your turnouts DCC Friendly, correcting the track alignment and wheel sets. This leaves operator error as the main culprit as the cause of the short.


Since the short is at the rails, the only items affected are the wheels and track. This short does not affect the DCC decoder and will not cause any damage to it, contrary to what some have said. Continual shorts will cause pitting of the wheels and track.


The reported short causing a bogie or ties to melt, is when there has been a short and the booster or circuit breaker has NOT tripped. Depending on how much current the booster can supply and the amount of time the short went unnoticed will determine the amount of damage. A 5 amp booster has the capability of supplying 60 70 watts of power, transformed into heat, it is a very large soldering iron. This will cause some damage and may cause a fire.


Adequate wiring is very important to enable correct booster and circuit breaker operation. Use the Coin Test to check all track wiring.


The 1156.


Using 1156 as a current limiter, on our railroads is nothing new. The use of can motors in our locos (last 15 20 years), that draw such small amounts of current compared to open frame motors of the earlier design, means using the 1156 to manage shorts and power division, is an ideal cheap device. Some of the draws backs of the previous 1156 usage on earlier layouts, has found it way into this 1156 DCC discussion. These draw backs are totally irrelevant now with our modern railroads with the can motors for the locos. Using the 1156s will not melt the ties as it has been reported. This is just another myth. The 1156 would only let 2.1 amps flow and earlier locos draw more than 2.1 amps and I did not hear any reports about the ties melting under the track while they were operating.


Present day locos equipped with a decoder and a can motor, draw about 200 to 400 mAs of current, while operating and 30 to 70 mAs while stationary. Sound locos only draw about 10 to 20% more. Two and three locos consisted together, including sound will only draw about 500 too 800 mAs of current. Using these figures as a guide and how you operate your layout, you can use the 1156 to divide your layout. Exceeding three or four locos in a power district may cause operational performance to be effected. Reduce the size of the power district. Remember with a few operators, not ALL the locos are running at the same time.


The characteristic of the tungsten incandescent lamp is that the cold resistance is about 10 to 20% of the hot resistance of the lamp. If we operate in this cold resistance area the 1156 will not impact on the layout but when there is a short the current is limited to 2.1 amps. This will allow total loco current draw of about 700 to 800 mAs before the voltage is robbed by the 1156 and starts to affect performance. If operating locos slowly as in switching operations, this still will not affect the layout. Reducing the voltage to the track affects top speed and the brilliance of any loco headlights. See below for results.


Wiring the layout using the 1156.


Some modellers wire each point frog feeder with a lamp.


My layout: I have divided my layout into 8 power districts, one per major operating area like a yard or station area. I will make smaller power districts when the operational need arises, if ever. This is easy to do, just make the district smaller.


Joe Fugates Siskiyou Lines layout: Joe divides his layout into train length power zones. See his video about using the 1156 at: Click on the screen to start the video.


See for a wiring diagram about the 1156 installations.



My club layout: When I joined the NMRA SIG group here in Sydney, their layout (booster) completely shutdown whenever someone ran against a point (turnout). They asked me if it was possible to prevent this annoying stoppage. I installed an 1156 on each of the 30 modules and connected that modules track to the 1156 and installed insulated track joiners at each of the modules track, where necessary. This now insulates each module from each other. As the layout has a continuous power bus that runs under the track with a single connection to all the track on each module, this was easy to do. Now when someone runs against a point (turnout), only that operator stops. All other operators continue operating and are none the wiser that a short has happened. Everybody is happy.


This layout is powered by a single NCE 5 amp booster. Operating nights have 6 to 8 train crews. This will mean about 8 to 12 locos as some trains have double headed locos. Broadway Ltd and Soundtraxx sound locos also are being used. Generally one train crew or maximum two in one module, each 1156 will only have at maximum 4 locos under its control. The 1156 is able to handle these loads.


I have installed an ammeter and it shows a maximum 1.5 to 2.0 amps during the operating session. At the moment, this gives us plenty of amps headroom with no need of an extra booster. Installing a full time ammeter at a convenient location, will allow you to monitor layout current (amps) demand. When the booster shuts down due to a short, the ammeter will be showing 3.5 to 4.5 amps while operating. This is when an extra booster is required.


I prefer to place the 1156s in a line side building as shown. If the operators loco stops, he will be suitably warned that he has a short. This illumination of the building will certainly attract his attention and he will remedy the fault immediately. This very visible warning will NOT go unnoticed for too long, thus preventing any problems. Some have asked that the light creates a lot of heat and is a little dangerous. 1156s are located in millions of motor vehicle tail lights and this is a similar small non vented enclosure has not caused a problem there. This is ideal manager certainly tells us what is going on when the loco stops. A loco stops and there is no bright visual warning, then it is dirty track that stopped the loco, upper photo. With a short, no problem missing the warning, lower photo. On my own layout, dirty track is a problem as I share the garage with two cars.


My own layout.


My 30’ x 30’ Double Deck layout is divided into 15 Power “town” Districts, each controlled by an 1156. Power Division for $30 and I have installed an Ammeter to monitor layout current demands. You will be surprised at how little current the layout uses.


Adding a PTC (Poly Switch) to the 1156.


Lately I have been modifying my 1156s that I have on my layout, after reading an article by Dick Bronson where he shows how to add a Poly Switch to a dual filament lamp. After approximately 40 seconds or so, the Poly Switch “cuts in” and now only allows about .4 Amp to flow through the Short. Click here for Dick’s Short Circuit article.



More Theory and Tests


The theories of how a lamp works see


To restrict the current when there is a short to about 2.0 amps we could use a 6 ohm 25 watt resistor, but using an 1156 lamp has the added benefit, that while it’s hot resistance is about 6.0 ohms, when the lamp is illuminated brightly, its cold resistance is only 0.5 ohm. This makes it a variable resistance resistor, with a range of 0.5 ohm to 6.0 ohms.


What this gives us model railroaders, when operating a few locos and drawing, say 700mAs (2 to 3 locos), the voltage drop across the 1156 lamp is about 1.0 volt. With a resistor this would be 4.2 volts. This voltage drop is robbing our layout of voltage. This affects the performance of locos namely top speed and eventually when the voltage at the loco (track) is at 9 volts DCC, the Soundtraxx decoders sound starts cutting in and out but non sound decoders will still operate to about 7 volts. The top speed will obviously be reduced, slow operation will be ok.


The table below the first 3 columns the current through the 1156 was with a DC Power Supply. The resistance of the 1156 was calculated by using Ohms Law R = E/I


My NCE DCC PHP system has 14.0 DCC at the output. I have an ammeter in circuit full time that uses a bridge rectifier connected in one track feeder. There is a voltage drop of 1.5 volts across this rectifier. I operate with 12.5 volts at the track with a 1156 in series with one power feeder to each power division.


For the last column of reading I adjusted my booster to give me 14.2 volts DCC at the track. The booster was adjusted to 15.6. There is a 1.4 volts DCC voltage drop across the bridge rectifier.


For DCC voltage measurements I use the DCC Tester from Pricom at


What can be seen as mentioned above, the 1156 gives you variable resistance and much less voltage drop than a 6 ohm 25 watt resistor that would restrict the current flowing to 2.0 amps when there was a short.


When the 1156 is used with our DCC layouts we can run about 3 - 4 locos (700 mAs) per power zone. If this creating some problems with the ammeter installed full time do as I can do, bypass the ammeter while operating and only have it in circuit when measuring loco current or layout demands. Alternatively adjust the booster to give you 14.2 volts at the track thus compensating for the ammeter (bridge rectifier voltage drop). I adjusted the booster for the last column readings and now back to 12.4 at the track.


Some modelers have reported by lowering their DCC track voltage has resulted in less problems with runaways and decoders. I operate at slow speeds with switching and no fast passenger trains, so I prefer my voltage lower.


Using an 1157 a two filament lamp with both filaments being used will provide a higher current about 2.5 amps and using two 1156s in parallel will increase the current to 4.2 amps. This may cause a problem with the booster sensing the short before the lamps restrict the current to the 4.2 amps. Experiments will have to be done here on individual systems as booster capacity and response times will be different.


Tests results of the 1156.


This shows how good the 1156s are for our DCC layouts. A very effective power dividing device that is cheap. The basic property of a tungsten filament of the 1156 acts as a variable resistance, that a normal resistor could NOT provide as it is a fixed resistance. Operating the 1156 in the range .1 to .9 Amps only creates a 2.2 volts voltage drop. A very acceptable condition that would allow 2 to 3 locos to operate, including sound, in that power district.


Using 1156s for Tonys Power Shields or the NCE EB3.


Experiment with 12 volt lower wattage lamps to provide the bypass lamp for the work around for these circuit breakers, to enable them to reset with sound locos. Using the lower wattage lamp will only allow a smaller current to flow through the short. 1156s will not cause any problems with decoders or wheels and these act as a very visible indictor of a short, that will be easy for operators to identify where the short is.


Bye the way, Jim Scorse at NCE recommends the 168 lamp for the bypass fix for the EB3s.





the 1156




the 1156

Voltage drop

6 ohm 25W

resistor by

Ohms Law


of the 1156

by Ohms

Law R=E/1

DCC track voltage

With 1156 and

Bridge rectifier

Ammeter installed

NCE DCC booster voltage

adjusted (15.6) to give 14.2 volts at the track with ammeter and 1156 installed

200 mAs
















































1.0 Amp











































































1156 illuminating with 3 locos & causing locos to slow up too much.


As mentioned in the text the lamp will start to glow with about .8 1.0 amps flowing through the 1156. With 0.8 amps and the track voltage at 13.8 volts DCC this would cause a reduction in track voltage to 9.6 volts DCC. Depending on current draw of locos, if double or triple heading locos with a heavy load could cause locos too slow too much. If this is happening then the 1156 resistance could be DECREASED by adding another lamp in parallel with the 1156.


An 1156 is a 12 volt 32 Candle Power (approx 27 watts) automotive lamp and connecting two in parallel would INCREASE the current when there is a short to 4.2 amps. While this would double the amount of locos before the two 1156s would impact on operation, it may cause the booster to trip out before the lamps restrict the current. Boosters trip in about 1/10 of a second. Also I am loathe to recommend a short circuit current of 4.2 amps continually running while there is a short. While there is normally no power dissipated at the short (wheels and track) there will be a bigger spark that will cause pitting of the wheels and track.


If your type of operation causes your locos to slow with one 1156 there is a couple of alternatives.

1.   Add a 5, 10 or 15 watt lamp in parallel with one 1156 to increase the current a little bit more. Experiment here start with a 5 watt lamp first.

2.   Wire two 21 watt lamps in parallel giving 3.4 amps as below. This does NOT cause the NCE booster to cut out and would be suitable.

3.   Buy a 1157 lamp which is a twin filament stop/park 32/5 CP lamp and wire both filaments in parallel.

4.   Adjust your booster DCC track voltage a little higher. See your system manual. NCE have a potentiometer that can be adjusted from the rear.


Try what solution is more suitable for you. If operating with 3 locos that cause the 1156 to illuminate dimly and slow locos that you cannot accept, it may be more appropriate to use circuit breakers like NCEs EB3s or TTXs Power Shields, as there is operating limitation with the light globe solution and the purpose of the lamps was a cheap alternative for power division and short management, but if the 1156 is affecting your operation, then this is not an effective alternative.


To connect two lamps in parallel:


Connect both the lamp bases together by soldering a link between the two lamps. To solder to the bases, clean the area with a file to enable solder to weld to the base.


Connect both solder contact tips together.


Solder a wire to each of the base and the contact links and connect in SERIES with one track feeder to the power district. It does not matter which track feeder you connect this lamp into. Yellow heat shrink from a previous test.


In electrical terms,


        SERIES means in line with a circuit and there is only ONE path for the current to flow through like the early Christmas tree lights, one globe blows and all lights extinguish. Ammeters are connected in series.

        PARALLEL means across the circuit, two or more paths for the current to flow. All the lights in your house are connected in parallel, one blows, and all others will still work. Voltmeters are connected in parallel.


Happy experimenting with 1156 lamps or similar, for power division and short management. I find the 1156 method a great indicator for showing why a loco stops and have them located on my layout in view in a line side building.


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