rail pick up wires

Discussion in 'DCC & Electronics' started by basementdweller, Aug 1, 2004.

  1. Today I measured stall amps in all my locos and determined which, if any, had insulated motors.

    I noticed that using a continuity meter, if I placed one probe on a motor terminal and the other on any wheel then there would be continuity, so how do you determine which is right side and which is left side rail pick up wire? This is on and older Athearn loco.

    I am sure someone will inform me of the digitrax decoders specifically for these locos, the problem is that some time ago I removed the tabs and got rid of that massive bulb in the cab, and installed a grain of wheat bulb for the no. boards, I planned on installing a MRC 350 decoder in this Athearn.

    Should I be checking for continuity between the motor terminals and the wheel or the motor terminals and the metal frame? I have read conflicting info regarding this.
    Thanks Martin.
  2. jwmurrayjr

    jwmurrayjr Member


    I think that you want to be sure that there is no continuity between any part of the motor and the metal frame. Like some of the old Athearn locos (They can be insulated.)

    Since most locos pickup via the wheels there will be continuity between the wheels and the motor terminals.

  3. Thanks Jim for clearing that part up for me, allow me to expand my question regarding the rail pick up wires.

    On the Athearn loco each truck picks up current from the left and right rail and then has a single "tab" for the metal strip from the motor to make contact with.
    As the decoder has separate wires for L and R rail current, how do I wire it so that the decoder gets current from both rails through each truck?

    Am I making more out of this than I need to? The only info I find on adding decoders to these locos is regarding using the Digitrax decoder made for this model.
    Thanks for any help. Martin.
  4. 60103

    60103 Pooh Bah

    Martin: are you measuring Ohms or just continuity with your meter? There should be no resitance between the wheels on one side and one of the brushes.
    Most of the older Athearns have one side connected to the frame and the other has a wire or brass strip. If your loco is this type, you need to get some sort of insulation between the motor and the frame. Then one wire goes to the frame, one to the other pickup, and the pair to the motor.
    Is there a way to isolate the grounded brush from the motor frame/body frame?
  5. David, I was measuring continuity only, thanks about the info regarding the wire going to the frame, that makes sense now. Thanks again.
  6. Alan B

    Alan B Member

    Take the red decoder wire and solder it the truck tower. To do this job really well take a length of red decoder wire and make a "Y" joint with the main red decoder wire. Solder one end to the front tower and one to the back. Cut the metal tab that connects the towers. I use just about one inch of the tab and only for mounting the decoder. For the black, there are three ways to connect it. One, is solder it to the light post. (Or use Digitrax's DHAT slide attachment.) Second is to drill and tap a hole in the chassis. Then put a 2-56 brass screw in and solder the black wire to the screw. Third is to solder the black wire directly to the metal clip that holds wheels. (You can also do the "Y" joint and attach the black wire to both trucks.)

    My first Athearn DCC installation, I used the Digitrax DHAT. After that, I just soldered everything. It's cheaper and works much better.
  7. Russ Bellinis

    Russ Bellinis Active Member

    To isolate your Athearn motor from the frame, remove the motor. Remove the strap that runs over the top of the motor from front truck to back truck and discard it. Take the motor out of the frame and carefully remove both clips that hold the motor together. Put what was the bottom clip (the one with the two tabs that contacted the frame) on the top. Put what was the top clip on the bottom. You can then remove the clips one at a time and solder the appropriate wires to each one. When you put it back together, the stock Athearn motor mounts will insulate the motor from the frame. You will also need to remove the stock Athearn "camp fire in the cab" lights, and run smalller bulbs wired directly to your chip at the appropriate wires. I don't remember all of the color codes, I use the instructions to wire the decoders each time.

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