Shorts, Power Districts, and the 1156 - Characteristics and Tests.
Test of the 1156 showing current & resistance readings.
See Joe Fugate’s video about using 1156s for short management.
Power Districts
When there is a short on the layout with only a single booster, the whole layout shuts down. While this is satisfactory for a single operator, it is very annoying when there are a few operators, all the trains stop when someone creates a short, normally running against an incorrectly set point or turnout. This annoying total interruption can be eliminated by dividing your layout into power districts.
Each power district can be controlled by a booster, circuit breaker or an 1156 automotive lamp. Boosters are expensive and not required if the layout is a running only approximately 10 locos at the one time or if total layout “current” requirements are less than the booster total capacity. Circuit breakers are less expensive (A$20 -25) per section but if the layout is divided into many sections, this can become expensive.
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 Fugate’s 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:
- An operator running against an incorrectly set of points or turnout.
- The back of a wheel contacting the closure rail on a turnout.
- Out of gauge wheel sets going through turnouts.
- Bad track alignment at turnouts.
- 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.
When this short happens and if “sensed” by the booster or circuit breaker by removing the power to track then everything will be ok. The tripping of the booster and the circuit breaker can only happen if all the wiring to the track is of adequate gauge. This is why the coin test is important.
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.
The 1156.
Using 1156 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 has made using the 1156 to manage shorts and power division 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.
The 1156 is a very cheap current limiter that if used correctly will give us short protection on our layouts. Using 1156s or similar incandescent lamps does not remove power to the layout. They restrict the current to 2.1 amps for the 1156. This 2.1 amp current will not cause any problems if the short is attended to.
Present day locos equipped with a decoder and a can motor draw about 200 – 400 mAs of current, while operating and 30 – 70 mAs while stationary. Sound locos only draw about 10 – 30% more. Two and three locos consisted together including sound will only draw about 500 – 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 -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 stats 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 Fugate’s Siskiyou Lines layout: Joe divides his layout into train length power zones. See his video about using the 1156 at:
http://mymemoirs.net/preview.php Click on the screen to start the video.
See http://siskiyou.railfan.net/model/constructionNotes/wiring.html 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 module’s 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 it’s “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 operator’s 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.
Install an ammeter to monitor layout current demands. You will be surprised at how little current the layout uses.
More theory and Tests
The theories of how a lamp works see http://home.howstuffworks.com/light-bulb2.htm
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, it’s 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 – 3 locos) the voltage drop across the 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 decoder’s 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 www.dcctester.com
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.
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 Tony’s 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.
|
Current flowing through the 1156 |
Voltage Drop across the 1156 |
Voltage drop 6 ohm 25W resistor by Ohms Law |
Resistance 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 |
0.1 |
1.2 |
0.50 |
12.2 |
13.9 |
|
300 |
0.17 |
1.8 |
0.57 |
11.9 |
13.8 |
|
400 |
0.26 |
2.4 |
0.65 |
11.7 |
13.5 |
|
500 |
0.43 |
3.0 |
0.86 |
11.3 |
13.1 |
|
600 |
0.7 |
3.6 |
1.17 |
10.9 |
12.6 |
|
700 |
1.1 |
4.2 |
1.60 |
10.2 |
12.2 |
|
800 |
1.6 |
4.8 |
2.00 |
9.6 |
11.4 |
|
900 |
2.2 |
5.4 |
2.44 |
9.3 |
10.4 |
|
1.0 Amp |
2.8 |
6.0 |
2.80 |
9.1 |
10.0 |
|
1.1 |
3.6 |
6.6 |
3.30 |
|
9.0 |
|
1.2 |
4.2 |
7.2 |
3.50 |
|
|
|
1.3 |
5.0 |
7.8 |
3.85 |
|
|
|
1.4 |
5.7 |
8.4 |
4.07 |
|
|
|
1.5 |
6.7 |
9.0 |
4.47 |
|
|
|
1.6 |
7.6 |
9.6 |
4.75 |
|
|
|
1.7 |
8.5 |
10.2 |
5.00 |
|
|
|
1.8 |
9.5 |
10.8 |
5.28 |
|
|
|
1.9 |
10.5 |
11.4 |
5.53 |
|
|
|
2.0 |
11.6 |
12.0 |
5.85 |
|
|
|
2.1 |
12.7 |
12.6 |
6.05 |
|
|
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.
- 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.
- 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.
- Buy a 1157 lamp which is a twin filament “stop/park” 32/5 CP lamp and wire both filaments in parallel.
- 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 NCE’s EB3s or TTX’s 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.