Direction lighting with bi-colour LEDS

[Southwell]

Hi all - i'm trying to put some DCC concepts bi-colour LEDS into a loco but it's slowly driving me mad. There's 4 of them, 2 in the front, 2 in the rear and obviously when the front are white the back should be red and vice versa. As such i've wired them up like so (excuse the dodgy paint diagram):

 

 

So resistors on all the -ves (not sure if that's right tbh as the whites are still brighter than i'd expect) and It's got a Digitracks DH126D decoder in it.

 

Clearly something's wrong because the red lights on the front are constantly on at a low level (whether the lighting function's on or not) and the directional lighting only seems to work when it's set to reverse. I've ruled out some dodgy soldering because I've redone it twice with different LEDS and the same result. Has anyone got any ideas? I'm not the best when it comes to electrics so I wouldn't be surprised if i've done something stupid.

Edited November 2, 2017 by Southwell

[Suzie]

You have wired it correctly. You have not stated which decoder you are using, but that should not be a problem if it is working properly.

 

I suspect that your problem may be due to some contamination somewhere causing current to leak into the LEDs which are supposed to be off. It does not take much current to light an LED nowadays - just touching one with your finger can be sufficient to give an indication.

[RAF96]

I use common anode 3mm diameter red/white 3-legged leds for directional lighting on Class 395 but they are suitable for any lighting situation that has the bi-colours in the same lamp housing on the loco.

 

The only consideration that is necessary is the value of the resistors in the cathodes to get the individual colour brightness as required.

 

I also use a 1K resistor in the blue leg to control the overall current flow to avoid overloading the decoder as my cheap and cheerful decoders have a 100mA limit and this can be exceeded if running 3 lights in front and 2 behind. This may be your problem as the decoder may be overloaded especially as you say the whites are too bright.

Rob

[Phil S]

Something which may assist in controllling relative brightness of the Red v White LEDs is separating them for each direction too - now that 4 or 4+ function decoders are readily available - with the  rewiring you are doing , why not ssing harwaredpearte front and rear lights, so that when a train is coupled behind, one end' lights can be switched off  (by using  hardware outputs 1+2 for the front, and o/p 3/4 for the rear.   Some decoders may also be able to dim the LEDs for a fine adjustment above the basic protection provided by resistors.

[Suzie]

Just use one resistor per LED - don't put them in the blue wire. 25mA per LED should be more than adequate.

[John ks]

Have you tried swapping the white & yellow wires over at the decoder?

If the problem swaps ends then the decoder is the most likely problem

if the problem stays the same then the wiring is the most likely problem

 

If the white lights are to bright then increase the value of the resistors for the white leds

[Southwell]

Thanks for the replies guys, starting to suspect it’s the decoder and I must’ve shorted it at some point.

 

I’ve only got a basic DCC controller so can’t reset it until I get enough cash together to upgrade. The motor control still seems fine though so the plan is to swap the decider out with another loco with no lights on it and then start again - the new one is a little more robust too.

[RAF96]

I refer you back to my previous post where I speak of not overloading the function outputs. I had a Hi-bright headlight, 2 front markers and 2 rear lamps at each end of my directional lighting output and the whole decoder played up (5 x 20mA = right on the decoder limit).

 

The decoder has self protection on the motor circuit but not on the functions, so I thought it was a gonner from a lighting point of view.

 

However after reworking the (Express Lighting Kit) lights by inserting an extra 1K resistor into the blue wire to better control the current I managed to salvage the thing and all is well now.

 

Just as well as the decoder was a one-off sound set incorporating police car horns for my Class 37 'blues & twos' loco.

 

You may find that by reworking your lighting currents the decoder may spring back into life - or not - but worth a try.

​Rob