https://tcsdcc.com/installation/ho-scale/1431
Why two resistors?
Only one bulb illuminates at a time.
Put one resistor in the blue wire and be done with?
Rule 17 allows for both locomotive headlights to be illuminated while yard switching, with the headlight in the opposite end of travel dimmed. It’s possible that the modeler was applying Rule 17 to his SW9 and wanted to ensure that the 820
Or independent control of both headlights. Always hated directional headlights in an engine, real engines don’t automatically do that. Best practices will always say to install a resistor on each individual LED.
Mark.
As has been covered, many modelers want the ability to have both headlights on at the same time so it’s not always one bulb at a time. That being said, however, if you do want to use only one resistor for both, you can, you just have to understand that if you do turn both on they will be dimmer than if only one is on because they will be sharing the current that is limited through that single resistor.
I’m pretty sure the DC wiring has only one light on at a time. I’ll check. But thanks for the confirmation that my rudimentary understanding of electrics is correct.
I understood that fitting a resistor into the blue common terminal could affect all features connected back to that terminal depending in where exactly the resistor got wired in.
Similar idea occurred to me with wiring number boards for my Proto 2000 GP 38-2 which don’t work properly with the TCS LL8 I installed. The bulbs are 1.5 v and the alternative wiring sources from the decoder outputs are 12v. I thought wiring the number board lights in series might drop the voltage while using only the one resistor. Wondering if number board lighting was directional or not.
There are TCS decoders with 1.5 volt function outputs. As for wiring the number boards in series, I’m afraid your bulbs are already toast. If you’re going to use bulbs it would be advisable to use 14 to 16 volt bulbs. Better to use an SMLED resistor combination. Wire in parallel to either one or two functions. As for directional, that’s in what you program them to act. You program the function just like head lights or whatever the decoder is capable.
Pete.
Thanks for this. The number board lights in my GP38-2 are 1.5v and were powered by the LL8 headlight and reverse light outputs so were not blown. The problem is the locomotive doesn’t run correctly in reverse with the numberboards lit. This is a known issue. If I knew what I was doing I could find the function outputs on the LL8 that deliver only 1.5v and solder the number board feed wires to those.
Until I get that information the numberboard lights stay will disconnected from the decoder. Checking TCS site the LL8 only has 1.5v outputs for front and rear headlights. The other 6 functions are all 12v outputs. So, if the front and rear numberboard lights are not directional (I mean in the prototype) then I’d wire them in series and use one resistor to drop the voltage to 3v.
Running my S2 today reminds me that both headlights remain on but the “back end” light is just dimmed to half intensity. That’s why you need to preserve the two separate circuits with a resistor in each one.
You can find the LL8 decoder info here. https://tcsdcc.com/1343
The solder pads are right on the end of the decoder. Just remember F1 and F2 are the headlight and reverse light. 1k resistors are cheap enough. I still recommend LEDs. I melted the shell on an Atlas RS1 from a headlight bulb and since then have used nothing else but LEDs and resistors.
Pete.
I’m sufficiently ambitious I bought two TCS AX4 to fit into my Proto 1000 C !iners. We’ll see how that goes.
Yes, LED’s use a lot less power, now come in appropriate colours and will outlast the locomotive they are fitted to. A lot less heat. At the moment I’m leaving those low voltage incandescents in place but any replacements will all be LED. Resistors are cheap and even my rudimentary soldering skills are up to the task.