Passenger Car Lighting

[Jim Banner]

Dave, thanks for asking.  How much current you can draw depends on track voltage and how big a heat sink you attach the LM317 to.  I use one of these circuits per car with no heat sink and it has no problem lighting all four lights.  You could use it power a second car but might need a small heat sink, say a 1" x 2" piece of 1/16" aluminum.  I have used a similar circuit with a 3" x3" heat sink to deliver an amp out at 18 volts in, but the heat sink ran too hot to put right next to plastic.  Based on that, you could probably use one circuit to power the lights in about 10 cars if you mounted the LM317 on a piece of 1/16" aluminum the size of the bottom of the car.  Whew!  Long answer to a short question.

If the rails are clean enough that the lights flicker only occasionally without the circuit, or with the circuit but with the battery turned off (I see I forgot the on/off switch in series with the battery) then there is very little draw from the battery.  With little draw, NiMH and NiCd batteries would probably go dead by self discharge before you ran them down in service.  I use alkalines because of their long shelf life.  Both AAs and 9 volt batteries work equally well.  In normal operation, you might have to change the 9 volt batteries once a year.  With the AAs, it will likely take several years to run them down.

To look a little deeper into batteries and battery life, let me say that I run on aluminum track, both indoors and out.  I can do this only because I oil the rails - one drop per rail every 100 feet.  This means I don't have very much flicker to start with - I would guess the batteries are supplying power to the lights only 1-2% of the time.  You probably have different track and may or may not oil it, but just the fact that you are running DCC means you are probably keeping your track pretty clean.  So I think you too would have very good battery life with this circuit and could stick with 9 volt rectangular batteries.  The built in battery compartment and on/off switch are convenient to use, and this leaves space in the washroom for the circuit.

[VirginiaCentral]

Jim, Great circuit! I think that might be just what I'm looking for.
Jerry

[rperego]

Jim - thanks.  Duh, I could have answered my own question about using a resistor because I'm thinking of a board in only one car and running wires back to the others - which is another way the draw will change depending on how many cars are hooked up, hence negating dropping with a resistor.

[Jim Banner]

I hope I have emphasized enough that I run on DCC and the battery life results I get are based on DCC.  If you are running on dc, this circuit still works when the train in running at medium to higher speeds.  But during station stops, for example, the battery will be powering the lights full time as the track voltage on dc would then be zero.

If anyone is intersted, I think I could redesign another circuit, one that I developed originally for charging Soundtraxx Sierra batteries, to work for lighting.  That would require a rechargable battery and would be charged from the rails by either dc or DCC.

[VirginiaCentral]

Jim, Yes, I would be intrested.

Jerry

[Pospete]

   with my coaches I stripped them down and replaced the bulbs with LGBs own 24v bulbs, also using a couple of LGB pick up axles to convert battery to track( though the exsisting switch)  As I'm on DCC I have the otion to have lights on or off, tho usually off.
    Just a thought for those running RC/battery locos, just wondered if anyone had thought of or tried again converting or using track powered lighting, then just using a power supply to feed the track power for coach car lighting?

[ED M]

I sucessfully converted over my two Pennsylvania coaches by purchasing two East Broad Top coaches & using two of the pickup truck assemblies on the EBT coaches & exchanging them with the truck assemblies on the PA coaches. It worked perfectly with no blinking at all & now all four of the coaches have track powered lights. I was going to buy the new EBT coaches anyway so it basically cost me nothing to convert the PA coaches. I am pleased that I no longer have to replace batteries & flip switches constantly!

[jviss]

Dropping voltage with a resistor can be a risky business, and this is one of the cases where it is.  How much voltage a resistor drops is proportional to the current through it.  So if you install a resistor sized to drop from say 18 volts down to 9 volts for 4 lamps, it will not drop enough voltage for the remaining three lamps if one burns out.  If the voltage drop decreases, then the voltage on the lamps increases.  With lamp life varying as the 13 power of the voltage, a small rise in voltage shortens lamp life radically.  Within hours, a second lamp will burn out.  Then, within minutes, a third lamp, and seconds later the last lamp will burn out.

For that reason, the circuit I use contains a voltage regulator.  It is shown below



In this circuit, a bridge rectifier rectifies the DCC track voltage to dc.  As the DCC waveform is rectangular, virtually no filtering is required.  A small capacitor (.1 to 1 microfarad) is connected across the bridge rectifier to keep the voltage regulator from oscillating.  Too large a capacitor here can overload the command station or booster on start up if many lighted passenger cars are used.  The regulator is an LM317 adjustable voltage, integrated circuit regulator.  With the resistors shown, it can be adjusted from about 7 to 12 volts output.  The output of the regulator and the output of a 9 volt battery are both connected to the lamp(s) through diodes.  With this arrangement, whichever source (regulator or battery) has the highest voltage will be the one that supplies power to the lamp(s).  I usually adjust the regulator output to be about .1 volt higher than the output of a fresh new battery.  This is easy to do it you connect a voltmeter from the output of the regulator to the positive terminal of the battery.  Then you are measuring the difference in voltage between the two sources.  If you connect the plus lead of the voltmeter to the regulator output and the negative lead to the battery +, the variable resistor can be adjusted until the meter reads +.1 volt (NOT -.1 volt.)  By keeping the regulator and battery voltages similar, the lights do not noticably change brightness when switching over between sources.

I usually build this cuircuit on a piece of perforated circuit board and hide it either in the washroom or under a seat, depending on whether I install AA batteries or a rectangular 9 volt battery. 

I know this thread is old, but it's great!  It's a shame that the circuit diagram doesn't appear. Does anyone know why this is the case, for me at least?

[DoyleS]

Since pictures are not hosted on this site, pictures need to be hosted on a separate site and often they then have an expiration date.  Best bet is to PM the circuit poster and he can send it to you in an email, or repost a new link on the site here.

[Hunt]

Since pictures are not hosted on this site, pictures need to be hosted on a separate site and often they then have an expiration date.  Best bet is to PM the circuit poster and he can send it to you in an email, or repost a new link on the site here.

Jim Banner died April 19, 2014.

[jviss]

That's a shame, thanks for letting us know.