Using DCC chip for LED(s) in DC loco

[Andre Anderson]

Harry,

The quick answer is using a DCC decoder to control just lights from track power would like using a sledge hammer to set finish nails. If all you want to do is run low voltage lights or LED's than a resistor in line with the lamp / LED would not only be much simpler it would be much cheaper.

The whole reason for DCC is to be able to control multiple locomotives on the same track, controlling the lights and sounds are just side benefits. When using DCC there is a constant 14v AC at 5amps current in the track at all times. You control speed, direction, lights and sound at the locomotive not at the throttle.

With each DCC locomotive is assigned a separate address that it listens for and only acts when it gets a packet of information with it's address on it. On most DCC systems you can set up to 10,000 address, I personally use the locomotives number as it's address number. The advantage to DCC is that a whole layout can be wired with just TWO wires from the system to the track. What I do is run a solid core 12ga wire around the layout and then run 22ga / 24ga solid core wire feeders to the track every 6 to 8 feet.

If you have any more questions please feel free to ask them,
Andre
Portland Oregon USA

[petersmith1942]

As you will have noted I broadly agree. Those most closely involved didn't want to widen the discussion
and don't want or need the main benefits of DCC. I, like you Andre, wouldn't be without them. On the other hand I don't want sound in every loco I have nor do I want to set routes or change switches with my hand set, or my cell phone!
Peter Smith

[jimowers]

Of course I would agree as well. However, the original question related to constant light in each direction. I cannot find a method that is as small as the DZ125. At approx.

[Harry Mantheakis]

Andre, thank you for all the information regarding DCC - I will keep that posting in mind should I ever get round to adopting DCC.

Jim hit the nail on the head: achieving constant light in each direction requires several components which, when combined, are very bulky (huge, actually) when compared to a small DCC chip. (I have done this using two different methods.)

When I think of how much of my own time I devote to individual items in my modelling, the cost of a DCC chip (which might save me time and enable me to achieve something that is otherwise not possible) does not seem so exorbitant.

Food for thought, at the moment. If I do adopt this option, I will post my progress.

Thank you again for all the feedback.

[Hugh Norwood]

If you use a DCC chip to provide lighting on a loco running under "normal" dc control, I do not think you will not get any light from the LEDs until the track voltage is (at least) greater than the Vf of the LED. DCC chips provide lighting on a DCC powered system when the loco is stationary etc., because there is always a voltage on the tracks. (As I understand it).

[jimowers]

You are right Hugh. There needs to be a minimum voltage to switch them on but then they are constant. The problem we have is getting a constant light whilst the loco is moving and this does work using the decoder. If you want the full monty with stationary as well as moving lights then you need DCC.
On another layout I am working, in larger locos, with Express Models SureStore which gives constant light in a single direction and also stationary. However, as has already been pointed out, such boards are very large and they also maintain the light even after the loco has changed direction.

[Harry Mantheakis]

I do get a constant LED light in either direction in a Chris Ward railcar using the Digitrax DZ125 decoder on DC. It also pulls away very smoothly at low speed.
I put all the instructions for installing these decoders in a OO9 News article last year.

I bought a Digitrax DZ126 and wired it up to a spare motor and a couple of LEDs on a breadboard. The motor does indeed start running after 5 volts, as per the documentation.

But the LEDs do not light up.

I asked the supplier (Douglas Stewart at Wickness Models - prompt delivery) about this and he told me that the LEDs will not work without DCC instructions.

So, Jim, I wonder if I could trouble you to tell me how you got LEDs to work?

Did you wire them up directly to the track supply? Or did you reset the decoder to allow them to work?

[jimowers]

It will work and I have used this method several times. However, there is a trick to it. Sorry that I did not mention this before...
If you require lights on your loco then there are the three additional wires on the decoder to use.
The only problem that I found at first is that it is rather counter-intuitive in that the common wire (Blue) from the decoder here is positive rather than negative.
After you have worked this out then the rest is fairly simple

[Harry Mantheakis]

It will work and I have used this method several times. However, there is a trick to it. Sorry that I did not mention this before...
If you require lights on your loco then there are the three additional wires on the decoder to use.
The only problem that I found at first is that it is rather counter-intuitive in that the common wire (Blue) from the decoder here is positive rather than negative.
After you have worked this out then the rest is fairly simple

[Harry Mantheakis]

I tried reversing the wires to the LEDs - blue for positive, and white (or yellow) for negative, but sadly the LEDs (which I checked, do function) failed to light up.

Perhaps this newer decoder model has been configured to prevent LEDs from being powered when running in analog mode.

Perhaps there is a decoder function setting that would switch them on in analog mode, but that is beyond my means - I do not have any DCC equipment with which to reset the decoder.

Heigh ho - it is back to bridge-rectifiers, resistors and LM334Zs for me.

The good news is that over the past year some tiny bridge-rectifiers have appeared that make it a lot more feasible to wire up the lights using the LM334Z method I have used in the past.