What am I getting myself into?

Model Railroader Electronics and DCC
1

I’ve got a couple Athearn BB GP40-2s that I’ve been planning on superdetailing for a while now. It is one of those projects I’ve wanted to do since I was a kid, despite there being more detailed GP40-2s out there, so I figured why keep putting it off.

The prototypes I’m following after have front and rear ditchlights, but they use constant ditchlights, allowing me to sidestep the issue of not having enough functions for flashing front and rear. I know how to solder and have hardwired a BB before, so that part doesn’t bother me at all. But that’s where I run headlong into the end of my knowledge.

Is there any specific decoder that I should be looking for? I’m not interested in sound.

I’ve haven’t done much work with LEDs before and only have the broadest understanding of their ways (the leads are sensitive to positive and negative, they enjoy resistors, etc.). How do I know what resistors to use? Or what wiring pattern to use for the four LEDs? Should they all go right to the decoder or, uh, some sort of power bus?

2

As you have figured out, you need a decoder with more functions than just motor control.

I’m not sure how other decoder manufactures number theirs, but with Digitrax, the 2nd number is the number of functions.

Like their DH123 has 2 functions, etc. 2 functions get you motor control and a front and rear lights. You can “cheat” and hook up the ditch lights to the front and rear lights, but you won’t have any operating options, such as flashing, etc.

You probably need some thing in the 4 function size.

Just my experience.

Mike.

3

Most decoders have a common (blue) wire and a function wire coming from the decoder.

I take the easy way out on LEDs…I buy them pre-wired from Dave at Evans Designs. They work on any voltage (use them for buildings too) and are guaranteed. For my money/time, I’ll pay a couple of bucks for the universal use capability and for no hassle.

4

You need to check the Athearn motor current, some of the older Athearn motors draw a lot of current. Be leery if the motor draws over one amp, a good running Athearn motor will pull just under one amp at full load. A six function Digitrax decoder doesn’t cost much more then a two function. The DH166 has a 1½ amp capacity and should have plenty of capacity to power a later Athearn BB GP40 with the goldish colored motor.

I might add the DCC decoders are pretty durable, I’ve been screwing them around since I went DCC back in 2005 and I’ve never dinged one. I did have one DOA out of the package but the manufacturer replaced it quickly.

I use my DH166 as my Guinea Pig in my locomotives before I install my sound decoders. I’ve been using the same one for about 4 years and it’s still going strong.

I use the NMRA 8 pin connectors in all of my locomotives as a standard and add a separate connector for the functions. My steam only uses headlight and backup light so no full function decoder needed. For my Passenger diesels I go with 4 function decoders to control the lighting in my passenger cars.

5

Basically a 1k, 1/4 watt resistor allows about 9ma current through an LED. They are current sensitive.

LED’s

http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm

Motor current I use with these meters.

http://www.trainelectronics.com/Meter_HF/index.htm

Meter for testing trains.

http://www.trainelectronics.com/Meter_Workshop/index.htm

I use four of these meters.

Mine read 13.6 vac on my NCE Power Cab. You milage may vary.

I use the voltage as a bench mark when the trains are running ok. Anything lower shows an issue but a loco has to be in the area as a load.

Rich

6

I like NCE decoders.

I think a 6 function decoder allows you to turn the ditchlights on and off the separately from the headlights F5 and F6. A a 4 function decoder requires them to be wired with the headlights, but since you only need constant lighting and directional with the headlights, that may be fine.

Also, IIRC, most modern decoders are able to handle LEDs directly wired, without the need for adding resistors. When you research, keep in mind many may already be “LED ready” so to speak.

7

Not so sure about that. Would it say so in the decoder manual?

I just read the manual for the DH166D, which would be my choice, and you still need resistors.

Possibly, maybe, some drop-in replacement board type decoders might be.

Do you know who’s decoders are LED ready?

Mike.

8

Many newer decoders have a variable power output for the lights that you can set with a CV. Older ones assumed you were going to use a 12v bulb so were set up to provide that much power to the light outputs. I don’t think there’s a list of which ones have that feature and which ones don’t. You just have to check out the instruction sheet or manual (which most / all companies offer on their website) for the decoders that meet your other needs (accessory outputs for example).

9

Generally you find built in regulation for LEDs on decoders that are “board replacement” type, because the latest versions of the locos that these boards raplce come with LEDs. BB locos don;t have boards to repalce with a decoder, they are strictly hard wire affiars. There are ways to finagle it but I think that is more effort than just soldering a few wires. Few if any decoders that end in plain wires or maybe an 8 pin plug have on-board resistors for LEDs.

1/8 watt resistors are all you need, even smaller than 1/4 watt ones. You can mount them on a small piece of erf board to keep the wiring neater, instead of having resistors all over the place. Larger (physical) surface mount types are smaller still but not too hard to solder, unlike the really teeny ones you can get. You could glue a row of them on a small piece of plastic and run all the wires to that point.

Remember if you put the LEDs up in the shell to use some small micro connectors to allow the shell and chassis to be separated. Slack in the wires works, but the excess can get caught in the spinning parts of the motor or drive shafts, the connectors allow you to keep the wires short yet set the shell aside without it dangling by the thin wires. FOr front and rear lights, you need a 3 pin connector - front light, rear light, and common. For ditch lights, if you want them to alternate, you need another 3 pin connector, left ditch light, right ditch light, and common. Or 2 pins for the ditch linghts and use the same common as the headlight - all the commons connect to the same blue wire on the decoder anyway.

–Randy

10

I studied the various responses here and cross-referenced by studying decoder diagrams on the different sites. Things seem a bit more straightforward than I’d led myself to believe.

One of the things you guys made me realize is that wiring the front ditch lights so that they can be turned on and off independently of the headlights isn’t really any more or less work than wiring them in parallel. I can live with the rear ditch lights always being on when I’m in reverse, but maybe it would be nice to be able to toggle the front on and off.

Randy: Do you mean something like these little guys https://www.amazon.com/Micro-3-Pin-Connector-100Mm-Female/dp/B01DUC1KEO for connectors? The shell being wired to the chassis is something that drives me a bit crazy with other locomotives, so…why not use some connectors.

I’m agnostic when it comes to the decoder brand, and I’m not sure that any two of my current locomotives have the same anyhow. The DH166D seems to fit the bill, so that’s on this weekend’s shopping list.

11

You can go to the Digitrax web site, and read the decoder manual for the DH166D.

http://www.digitrax.com/

The search box at the top right on the home page, type in DH166D.

It’s all in there, as far as installation, CV’s, and ditch lights. You can scroll down to page 55 of the manual, and see how the ditch lights are wired, and what CV’s to set, for rear ditch lights, and the flashing effect.

Their decoders use the 128 speed step as the default. I don’t change that, every loco starts to nudge and creep at step one, which is what I like.

Getting the decoder with the plain harness is the way to go, as Randy points out, the BB engines don’t have any excisting light or function boards.

I’ve done quite a few BB hard wire conversions.

Mike.

12

I don’t want to confuse the issue by asking a different question, but…

How do you normally convert a BB to DCC? I would think you would use a "board

13

Someone else will probably answer before my moderated post get posted. (I was a bad boy in the diner)

Replacement boards snap on and off, where the circuit board snapped on and off, to little plastic tabs. This means you loco had to have been a certain age, to have such a standard sized circuit board. BB’s didn’t have that. My LL Proto 2000 GP9 had a much shorter circuit board than the replacement boards.

If you look at older how to videos on youtube, you will see they use a digitrax DHAT connector, which is no longer available, to replace the clips across the top and bottom of the motor.

There is no place to mount the replacement board, and you have an uninsulated board flopping around, waiting to touch other metal things like flywheels. The other decoders come wrapped in heat shrink and are shorter than replacement boards. They are easier to fit in the tight confines of a BB.

14

I’ve found the easiest for BB locos is the hardwire, just the bare wire harness on the decoder, no socket or plug.

There are many different ways to create “boards” or “platforms” to seperate the wiring, keep wires from moving parts, and give a place for the decoder to sit. Some use styrene, or cardboard. Just keep in mind the space your using.

I just usually use kapton tape, and tape the decoder to the top of the motor, after I have “bundled” up the wires, and secured with the same tape.

Not all boards will fit in the body shell of a BB loco. If your going to go that route, check the width of the board, and the space in the shell.

I had collected a bunch of the Athearn light boards, thinking it would be the easiest, but not so much. They don’t accept LEDs, only the Athearn bulbs. Plus, by the time I would’ve connected wiring to a board, I could have hardwired it, much simpler.

If your going to use a “board”, at least find something that is friendly with LED lighting, or you still have the added wiring of using resistors.

Then you still have to mount the board. Some have the clip that will clip onto the top of the motor, making one of the connections, but most don’t, they’re held in with screws.

I’ll stick with hardwiring.

YMMV.

Mike.

15

Yes. Back when I used to install directional light boards in my BB, I would use double stick foam along the top of the motor to secure the board. If I was going to convert BB to DCC, I would have just naturally installed a board replacement style decoder and soldered everything to the pads, but maybe the shrink wrapped type with all of the wires folded up works better. I would think intalling LEDS with resistors would lead to overcrowding, so I naturally just suggested the “led ready” dcc board decoders.

16

I’m not knocking the boards at all Douglas. I can see how it would work. I’ve actually never tried a board type decoder, something to consider.

If your going to add sound, it’s probably the way to go.

I’ve been using LEDs from Evans. The are ready to go, which helps with the install. Cost a little more, but I think it’s worth it, especially with a wiring “challanged” guy like me.

My only real experience with boards is the Athearn light board, which I remove.

Mike.

17

Wait, you hard wire most of your decoders, but consider yourself “wiring challenged”? This does not compute. If you can hard wire a decoder you are anything but wiring challenged. I mean, that’s a whole 4 wires just to get the motor to run, plus another 4 for basic lights. It’s only 2 more connections to put your own resistors on LEDs, and there’s no thinking involved - it’s a 1K resistor, and the resistor doesn’t care which way you orient it, nor which leg of the LED you connect it to.

I will buy pre-wired SMD LEDs if I need them for anything (my era doesn’t have ditch lights) but only because my vision is too poor even with magnifiers to even attempt to solder the wires to those little things. As in, it’s not blurry, it’s completely blanked out over a certain area of one eye.

–Randy

18

OK Randy, I do have problems with containing the “mess” and adding resistors seem to clutter things up more.

It seems no matter how I “fold” things up, once the shell is on, I usually say to myself, “hopefully I won’t have to take this off for a while” [(-D]

Maybe I’m just lazy, but I like the Evans lights. Especially since my time period means ditch lights.

The peco size LEDs I get are perfect for that.

Mike.

19

Like I said, I can’t even see those itty bitty LEDs to solder them. THe 3mm size for regular lights though are no problem.

If I had a lot of LEDs that needed resistors, I would use a small board to mount the resistors on instead of leaving them float free. Before they went out of business, Ulrich used tohave the perfect thing, a small circuit board with surface mount resistors already soldered one, so you just had pads to attach your leads to, with up to 6 resistors, easy to keep things neat. The more adventerouse could get just the boards and solder their own resistors to them, but once again these things are now most likely beyond me, or I would make up m own version of such boards, it’s not exactly difficult because there’s no ‘circuit’ really. However, unless space is super tight, a small piece of perf board with some 1/8 watt resistors stuck in it serves the same purpose.

LEDs that attach to the shell should get short leads and some micro connectors instead of leaving long leads to lay the shell to one side. Mine are simpl,e so for example an Atlas RS-3 for me only needs a small 3 pin connector for the front and rear lights plus the common, there are no rooftop beacons or split headlight where one is a regular headlight and one is a Mars light. Short wires plus a connector mean I can completely take the shell off but also don’t have to worry about wires dangling around inside around the spinny bits. Yes that’s even more connections but such is the way it goes. For locos where the lights are in the chassis, like my P2K GP7s, I snp off the wires only slightly longer than the minimum needed to read from the decoder, so there is enough wire left to hold while stripping it, and room to slide the shrink tubing on. Once I measure to length on the loco, I usually wire it all up off the loco, except for the track pickups and motor wires. It’s pretty easy on the P2K locos since there is a top chassis piece that goes over the motor/flywheels/driveshaf