Through-wiring an EMU that's not DCC ready

[tjf4375]

Hi all,

Hope someone might be able to offer some advice here 🤞

I've recently taken the plunge and switched my layout over to DCC, and I have no regrets so far! However, one of my multiple units, which is not DCC ready, is causing me a bit of a headache. Because it has bi-colour LEDs for the head and tail lights, there are PCBs in the front and rear coaches that switch these from red to white depending on the direction of travel. This worked fine on DC of course, but obviously for DCC it's a different matter. The motor coach for the EMU is in one of the centre trailers, so initially I looked at separate function decoders for the front and rear coaches to control the lights. However, this won't work in this case, because the PCBs for the head and tail lights have a single track feed input, and then use some electronics to switch the bi-colour LEDs according to polarity. As such, the only option I'm left with is using the motor output of the main decoder. 

This means I have to find a way to 'through-wire' from one of the centre trailers, to the front and rear coaches. I've looked at various socket connectors but can't seem to find one that's small enough for this purpose. Does anyone have experience of through wiring between coaches that they could share? I'd really appreciate any advice or pointers for this!

 

Many thanks,

Tim

[jamesed]

I'm going to assume you are OO so you've got a bit of space to play with.  If you are N gauge then fitting in what you need may be an issue.

 

I think your first instinct was correct. It will be a lot simpler to have a decoder in each of the end coaches. Any old 2 function decoder with wired outputs will do the job. It doesn't matter if it's a function only or standard decoder, just buy whatever is the cheapest you can get your hands on that is a suitable physical size. It will be easy to install because you've already got pickups wired to the lighting pcb.  Just snip these wires half way along and connect the pair of wires from the pickups to the track wires (red and black) on the decoder.    Then you'll need a 3 wire to 2 wire converter. There are plenty of these around (look at DCC Conccepts or Rails of Sheffield who both sell them. There are plenty around because Kato users need them all the time and they are typically about £8 for a pack of three.    Simply connect the common positive (blue), function output A and function output B (yellow and white) to the 3npin side of the converter and then connect your pair of wires from the lighting pcb to the other 2 pin side of the converter. Then program the decoder address. The function outputs should by default be mapped to F0f and F0r.  Hey presto it should all work fine. If both cars are showing the same colour at the same time just put one back on the track and add 1 to the default value of cv29 which will sort that out. 

Edited January 29, 2023 by jamesed
to correct typo cv29

[WIMorrison]

48 minutes ago, jamesed said:

add 1 to the default value of cv19 which will sort that out. 

I think you mean CV29 😉

 

Also, before changing CV29 read the value - if it even then add 1 or o the value, and if it is odd then subtract 1 from the value.

[JDW]

I'd be inclined to agree that the thought of wiring them together is not the way to go. I have a fleet of DMUs, and find the Hornby 142s (wired together for reliable pick-up) and Bachmann 150s (which I leave coupled to avoid damaging the delicate coupling mechanism) a nuisance to put on or off the track. My Bachmann 158s were some of the first to get DCC many years ago, and have the same two-wire layout from pick-ups to lights on the non-powered car. It's an added cost, but much easier than trying to couple up tiny connections. I forget how it was done now, but I didn't even use a tow wire to three wire converter, just soldered the wires from the decoder to the relevant places. I'm not at home to check just now, or I'd post a picture. 

[jamesed]

31 minutes ago, WIMorrison said:

I think you mean CV29 😉

 

Also, before changing CV29 read the value - if it even then add 1 or o the value, and if it is odd then subtract 1 from the value.

Oops, thanks for correcting that Iain. I did indeed mean cv29.  I'll go back and edit the previous post just in case anyone refers to it in the future.

 

You are, of course also right about reading the value of cv29 but in this case I was assuming the decoder would be new with default settings or at least have had a reset routine done on it first in which case just add 1 should be all that may be needed.

[tjf4375]

Thanks loads everyone, this is all really helpful - James you're right, I'm OO gauge so should be plenty of space. I have bought two function decoders from train-o-matic, but couldn't work out how I was going to get around the problem of the bi-colour LEDs, but I think I was over-thinking things. The functions on the decoder take care of simulating the polarity switching of the track feed. I shall go and seek out some 3 to 2 wire converters now, may need to come back to you for a bit more guidance before I wire everything together if that's ok!