Retro-fitting directional lighting to a Class 37

[Smudge617]

Hi

I'm still new at this. so please bare with me, I would like some advice. I intend to fit Directional lighting (no cab lights) to a class 37 loco, something I've never tried before, I think I have the wiring sorted to/from the decoder, (I'm using DCC) My question is do I need to fit a resistor to each LED or can I use one resistor for each set of lights (making four resistors in total) or does anyone know a different or better way of doing this, I am not electrically minded so anything I need would have to be bought and simple to install/solder.
I know of a company called Illuminated Models who make these type of things, but having spoken to a friend of mine who bought one, he suggested fitting my own LED's as their version sits too low and to make fit I would have to cut a large section out of the chassis to make room, also they do not have a template I could use to mark out where to drill, making that process a bit hit and miss.
Any thoughts would be appreciated.

[Mick Bonwick]

There are several Class 37 options in this range:

 

https://www.expressmodels.co.uk/catalogue/head-and-tail-lights/dcc-locomotive-lights-4mm-scale/dcc-lights-for-diesel-locomotives-4-function

[Sir TophamHatt]

Welcome @Smudge617 - you sound like me.
I have no real idea about electronics and schematic diagrams may as well be written in Chinese!

 

However...
What you want can be done and fairly easily.  Here's some questions:
 

Will you be fitting lights at each end?

Will these be bi-colour LEDs or will you have two red LEDs and two white LEDs at each end?
Is the DCC chip in a socket or bare wires at the end?

 

I will dig out some diagrams I drew to help me add lighting - I have done both bi-colour (which was only half successful) and dual colour in a German 218 loco (still a little proud of this).

 

I used one resistor (1K) per LED.

If we make it simple and say you just want a couple of white lights at one end, if you used one resistor (as I understand it), the power running from the chip to the light would go through it and then split between two LEDS, therefore each LED would get just 0.5K of resistance.  This would make them brighter.  I may be wrong (someone else will be along shortly to confirm).  I guess you could add a 2K resistor but I don't really know.  Safer to use one per LED.

 

There's quite a few threads (don't let your head get blown off!):

 

 

[Roy Langridge]

Take a look at Stickswipe on eBay - he sells some cracking kit and will customise things if you ask. All comes with the resistors fitted and instructions. He does both DC and DCC kits.

 

See: Stickswipe

 

Sir Topham:  Resistance is not split. Ohms law says Volts = Current x Resistance.  As volts on the blue wire is fixed and the resistor is fixed, the current is then fixed. That available current is then shared across the LEDs if they are wired in parallel.

 

Or in really simple terms: Imagine that you have an amount of water flowing (volts) and you put an obstruction in the way (resistance) the flow of water will be slowed (current). When that flow of water reaches a branch it can go two ways. Assuming the two branches have the same path (i.e. identical LEDs) then an equal amount of water will flow each way - but each will have half the flow of the whole.

 

Hope that helps.

Roy

[Smudge617]

Great, thanks both of you, I had thought of using bi-colour LED's but it would  look weird, so I intend to use single colour LED's with a Laisdcc 1K Ohm 1/8 SMD resistor board with it.

 

I have tried using a pre-made light board (not by Swiftstick I might add) but after a few minutes faffing around trying to make it fit realised that the board was too deep and I would have to modify the chassis to make it fit, then the wires broke on both light boards so binned that idea, also trying to work out where to drill holes not knowing where the board was inside the body is beyond my expertise.  But I will contact Swiftstick and see if he has a solution to that, as I have several old Class 37's I would like to modify.