LED in Parallel with Incandescent?

craftech Oct 5, 2022

  1. craftech

    craftech TrainBoard Member

    44
    2
    18
    I have someone's older Bachmann HO passenger car set. I installed a sound decoder in his engine and he wants more light in his 3 passenger cars.

    With the roof removed there is a single incandescent light in a well in the center of an acrylic light diffuser that runs the length of the roof. There is room in the well for a 3mm LED as well. The 3mm LED has a resistor and rectifier already on the leads.

    Short of not having a keep alive (although according to Evans Design there is also a capacitor under the heat shrink along with the rectifier) is there any downside to running them both on DCC in parallel? It will be a simpler job than a complete LED conversion. Will the heat from the incandescent bulb touching the LED be enough to cause the LED to fail?

    Thanks,

    John
     
  2. acptulsa

    acptulsa TrainBoard Member

    2,906
    3,500
    69
    As long as you specifically get the LEDs designed to work with DCC, no problem wiring them in parallel.

    Heat is a different story. It's a problem. There's room for the LED because the bulb can get warm enough to melt the acrylic. Most LEDs will melt even sooner. Why not get two for each car, and mount them 1/4 and 3/4 of the way from the front? It's possible to drill holes in the diffuser for them. It might work even better to mount the LEDs at each end of the car.
     
  3. Mike VE2TRV

    Mike VE2TRV TrainBoard Member

    3,714
    6,767
    81
    Go for a complete LED conversion. It's easier, uses less current and they won't burn out like an incandescent. They might stop working for other reasons, but that depends on the circuitry around it. A fast rectifier and resistor in series with the LED protects it from reverse polarities (LEDs are notorious for their very low reverse breakdown voltage - around 5 volts DC). Also, try to use "warm white" LEDs for a more realistic appearance.

    There are some LED lights available that have a full-wave rectifier bridge and drop resistor built in (in a heat-shrinked bundle close to the LED). I love those for converting locos from incandescent to LED light. They're very small, with long thin leads, and can be glued in just about any nook or cranny inside a passenger car or a locomotive. I haven't seen those in train shows for a long time, unfortunately.
     
  4. craftech

    craftech TrainBoard Member

    44
    2
    18
    Thanks guys for that info.

    I think I will just do the conversion. The idea that Tulsa had about one on each end sounds like it might spread the light better and the all in one bridge rectifier and resistor under the heat shrink is what I have from Evans Design. I have 3mm that operates on DC, DCC, or AC and some of their super bright SMD type wired the same way. The only thing missing is the Keep Alive cap, but I would have to cut the leads to the LED to add that.

    I also have strips that operate at 12V, a reel and also some individual 3 LED strips with leads. I would need 2 resistors (or 1 resistor and trim pot) , bridge rectifier, and cap for those, but they would probably spread the light very well. I could attach them to the acrylic diffuser facing down or maybe facing in?

    John
     
  5. Mike VE2TRV

    Mike VE2TRV TrainBoard Member

    3,714
    6,767
    81
    I used a short warm white 12V LED strip for an RDC's interior lighting (everything built into the strip), but I had to cut down the brightness with an extra resistor in series and a long strip of car window tinting film, and a full-wave bridge ahead of the whole shebang. Doing that job brought on a bit of cussing but it was fun.:)

    I'm starting to believe that cussing is a necessary step...;)
     

Share This Page