DCC decoder in Märklin Pacific/Mikado steam

I put a DCC decoder in my 2 Märklin steamers. I also wanted firebox flicker. Robert Ray has done this before and has archive photos. Decoders are smaller now so much easier.

Lenz Silver Mini, Digitrax DZ125 or CT Elektronik are the only ones that will fit under the cab roof. CT Elektronik is the smallest but will have unfamiliar values for many CV's beside the standard NMRA ones. Lenz defaults BEMF on and it does really strange things with Märklin motors !! Lenz and CT only have 0,5A motor current rating and Märklin motors are all over the place current-wise. They typically draw at LEAST 0.1A, many draw 0.2A and motors that are heading for failure can easily draw up to 0.5A so be careful with any decoder. Digitrax easily fits and can handle up to 1A but I wouldn't trust that spec. BEMF is NOT turned on with Digitrax.

Cut the inside cab roof tab. Observe all the locations that could make contact with the decoder wires. Make sure you put tape inside the shell to prevent shorts. DO NOT PUT TAPE ON THE DECODER ! The yellow tape below is to hold in place while I solder everything.



Cut the wires from the frame pick up to the motor. Careful because the capacitor wires that hold the brush tension can also now slide out. Use tweazers if you have to put them back in.


Solder the red and black power pickups to the frame leads. Red to the right.
Solder the grey and orange wires onto the motor and insulate. Orange to the right.


Should look like this:


LED headlight next.
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The LED head light is easy but the wires to it have to be small. Some decoder wire is but most are not. TEST FIRST !

The incandescent lamp mounts sort of low on the front. I mounrted a large LED so that it illuminated well (not bright, but distributed) and did not have to be so specific about location. I put a piece of Kapton tape over it to make that ideal very sligthly yellowish incandescant color. There is not a lot of room in the shell so I mounted the LED resistor to the LED itself, on top:



Firebox flicker next.
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The firebox flicker LEDs were a pain. There is a small gap between the shell and the sides of the motor. Good start. I had some side mount amber LEDs great. I mounted then right at the shell's bottom edge, out of sight but as low as I could to get light out of them. You really do not see the light intensitiy of the incandescants so you have to get them as low as you can.

The LED is the horizontal metallic band with the translucent half round below it.



The motor housing is plastic so I CA'd the LEDs to it. MAKE SURE YOU PLAN THE POLARITIES (and the opposite side's polartity ! ) The frame is metal so I used Kapton tape to insulate.

Since there was is little room, I used a surface mount resistor right on the LED with Kapton under it so it doesn't short to the metal frame. Actually, you can connect any of the Function lamps tp the motor frame (track power) but the brightness will be about 1/2. But in this case, I can't solder to that large frame !

I wanted as much light and because the firebox is in the middle of the cab / boiler, I put an LED on the other side and wired in series. There wasn't an easy way to get the wire over to the other side I just went through the motor's brush area.



LED's are about 1.5 volt each so two in series is about 3 volts. DCC function voltage is at least 10V, maybe as much as 12. Use 12 for easy math - 3 volts for the LEDs leaves 9V and I wanted 100 milliamps (0.1A) thru the LEDS Lets round down to 90 ma (0.09A) and we get 0.1K (1oo) ohms. R(ohms) = Volts / Current(amps).

 

Thanks for posting this! The photos really help. :thumbs_up:

 

Thanks for the photos and the great work Jeff. My next DCC projects are a Marklin 4-6-0 and a 2-8-2.

John

 

Jeff, is your shop ready for orders?

 

Jeff,
That looks nice, it has been a while since anyone talked about some DCC stuff here. For the LED current I think you meant 10ma and 1K. Can you post some videos of this loco running on dcc with the lights and special effects ON...
Kim

 

Yes nice pics and explanations Jeff.

Thanks Kim, I was also confuse about the resistance value.

Here is what I use for my led calculation.

Resistor calculation

Ben

 

An excellent article and photos, thanks.

 

Kim, yep 1K gives about 10ma. but the LEDs are low lumanence ones and since they are 'pulsed' for the random flickering, they can take 50-100ma. So I used 220 ohms. Still not easy to see. Nothing like incandescents but the current is so high with bulbs.
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