N scale to HO

Discussion in 'DCC & Electronics' started by lester perry, Aug 23, 2008.

  1. lester perry

    lester perry Active Member

    I am still in the process of changing from DC to DCC. I have a Thomas engine for Grand son that is very small and little or no room in it for decoder and forget sound. Today I got an N scale decoder that I think will fit but I don't want to fry it, it is a .7 amp decoder. What do I need to do?
  2. 60103

    60103 Pooh Bah

    Do you have a ammeter? Put it in series with Thomas and see what he consumes (Full speed, hold onto the coupling). If it's under .7 amp (and I expect it will be) the N gauge decoder will be OK.
    I remember one of the magazines commenting about one new loco how it was nice that they had provided to decoder socket, now if thy had only left space for the decoder.
  3. steamhead

    steamhead Active Member

    I don't think you'll have a problem. I'm using a Z-scale decoder on a a B'mann HO 4-6-0. I had planned to use the N-Scale decoder, but was informed Digitrax had discontinued the N-scale line as it was essentially the same as Z.
  4. Russ Bellinis

    Russ Bellinis Active Member

    I am running an n-scale m1 decoder in a p2k Sw7. In order to make sure that I didn't fry anything, I wired the lights directly to track power and all that the decoder operates is the motor.
  5. MasonJar

    MasonJar It's not rocket surgery

    You will likely need to measure the amps drawn under stall, not just under "flat out" conditions. At least this is what my Digitrax decoders call for. You need to run the loco as David describes, but push down so the wheels (momentarily!) stop turning. This is when the loco draws the most power, and is what will fry the decoder. It is this value that will help you decide if the decoder is appropriate or not.

  6. pgandw

    pgandw Active Member

    I have to disagree with this approach, especially in light of the relative prices of locomotives and decoders these days.

    Disclaimer: The following does not apply to locomotives with traction tires; these will usually stall before slipping their drivers. Stall current would be the preferred rating when a locomotive has traction tires.

    None of the electric motors currently in use will survive very long being stalled with power on. The stall current is too high; the motors overheat, short out, and burn up (it generally takes a few seconds for this to happen).

    The only exceptions are the stall motors used on Tortoise and similar turnout motors. These motors are designed to be safe stalled with power on. The downside of the stall motors is insufficient torque to power our locomotives.

    Almost all locomotives (again, assumes no traction tires) in the smaller scales will slip their driving wheels before the motor reaches its maximum continuous current. FWIW, this is the way to safely weight your locomotive for maximum traction. Add weight until the wheels start slipping at the maximum continuous current rating of the motor.

    You can then safely use the motor current with drivers slipping as a basis for choosing a current rating for the DCC decoder. After all, you are never going to see a stall current in real use on a layout.

    Another upside: Should you somehow manage to get your locomotive locked up (wheels can't turn) with the power on, if the decoder is rated less than the stall current, you will likely fry the decoder instead of the motor. Since new decoders are easier to buy, cheaper, and easier to install than a new motor, I would rather fry the decoder than the motor.

    But I've yet to see a derailment that locked up the drive wheels, but kept the power flowing. And you don't have to stall the motor, and chance it's overheating, to find the slip current. Simply block the locomotive from moving horizontally, and measure the current when the wheels slip.

    For these reasons, I prefer the slip current for rating my decoders. I suspect the Digitrax advice was written back in the days when decoders cost more than locomotives.

    my thoughts, your choices
  7. MasonJar

    MasonJar It's not rocket surgery

    Excellent perspective Fred. Thanks for the "counter balance". The Digitrax instructions are a bit sparse.


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