Digitrax Back-EMF

Discussion in 'DCC & Electronics' started by platypus1217, Mar 1, 2009.

  1. platypus1217

    platypus1217 Member

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    Has anyone ever set up the back-emf features on a digitrax decoder? It seemed like a bit of work going through the three CV's and indvidually incrementing them to find the correct value as described in the instructions. Is it worth it?

    I tried turning them up pretty high and I still had to crank the throttle up to get it to move. I was expecting that the back-EMF would help the motor get started at slower speeds. My understanding was that when the engine starts off at a low voltage that isn't quite enough to turn over the motor the decoder should keep increasing the voltage until the motor turns over and generates some back-EMF that is consistent with low voltage that is being applied to it. Is that how it is supposed to work?
  2. steamhead

    steamhead Active Member

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    I'm no expert, but.....Back EMF is a feature of the decoder which allows it to monitor motor speed and automatically compensate power to the motor to maintain a constant speed.

    What you want to achieve is controlled by the variable VStart, which is CV #3.
  3. diburning

    diburning Member

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    No.

    To change the start voltage/speed, it's CV2. Atlas units are generally around 10, Athearn can be 50+, proto 2000 should run ok out of the box. I'm not too sure about other brands but the numbers above are general numbers. My Athearn SD50 is at a value of 73 to get it to crawl at speed 1.
  4. steamhead

    steamhead Active Member

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    Diburning..is right. It's CV2. I mis-read my CV card....:cry:
  5. platypus1217

    platypus1217 Member

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    I got the top speed of my two locos matched up ok last night. But they have different starting inertias so once you go below 3/4 throttle they start to get out of synch.

    I was half tempted to go out and get a scale speedometer and USB interface so that I could write a program to do it for me. Just put the train on the track and tell the computer the scale speed curve that I want the engine to have and then let it do the work of figuring out what values to use in the speed table.