Wiring a DC variable speed motor.

  • I need the motor I have from a treadmill for another of my projects. I’m going to try to wire it up tonight, and rig a cheap controller for it. If you’re at the space, you might do a ride-along and get a “how to wire up some stuff, use an oscilloscope, maybe do a quick coupler on the lathe” session. Not really a workshop, but if people are interested, I’ll show them what I know.

  • Member

    Well damn if I had known that was what you were doing tonight…

  • So this is the smaller one. I looked inside of it and noticed it had a 12 reg.
    So I never got it to work till today. I used 14v or 15 to make it work.

    Operating Voltage: DC 12V/24V/36V/60V
    Rated Current: 8A
    Max. Current: 10A
    Control Power: Max. 400W
    Speed Control Range: 10% -100%
    PWM Frequency: 21KHz
    Item Size: 90 * 40 * 3mm / 3.54 * 1.57 * 1.18in
    Item Weight: 79g / 2.8oz

  • I have this 2.5HP 90VDC treadmill motor I want to use to power some tools in my garage. I’d ideally like it to be variable speed, closed loop and reversible when I get finished.


    The control board that came with it is kind of a pain in the ass, and I don’t have all the pieces, and also the guy that originally scrapped the treadmill chopped up the wiring harness in the process. So I was going to try to use this SCR controller, maybe with a bridge rectifier to get the pulsed DC I need… If the voltage range out of the controller goes out of range for the motor, I can do a voltage divider or something to put it in the right ballpark.


    I got several of these controllers from Deal Extreme two years or so ago and have used them to control heating elements before. In theory they should drive a DC motor though.


    I looked inside, and spotted what looks like a tiny bridge rectifier in there. Maybe it outputs pulsed DC? One can only hope… Then ask the 'scope to confirm it.


    There is a fuse in the thing, and the pot is a 2 watt, 470k ohm job… that’ll be useful to know if I go to replace it with a digital pot and close the loop.

    I hooked it up ghetto fabulous style to the handy DC supply and confirmed that the motor will spin given DC power. That is a good sign, because if it were dead from previous experiments I would not want to spend more time on it.


    Unfortunately the SCR supply was labelled in Chinese and I think it might be dead. I hooked it up to the variac and a 'scope and tried to confirm that I’d guessed the wiring correctly, to no avail. The output voltage appears to be entirely unaffected by the pot on the device, and it seems to put crazy noise on the input side. IDKWTF is wrong with it. I did give my self a pretty decent shock though. Luckily I had it plugged into the variac, so it was likely only around 60VAC, and it was isolated by the variac. I’m not dead yet, but I think I’ll try to source a better SCR driver for this motor.

    Plan is to get it speed controlled open loop, then hook up the RPM sensor (quadrature optical encoder with a slotted wheel) on the back of it to an arduino, then add an RPM display, remove the pot on the board and replace with an I2C digital pot, and re-attach the original pot to the arduino as an analog input. From there, you can dial in a desired RPM, and the arduino can sense real output RPM and adjust the digital pot as needed to account for load. A simple PID algorithm should give stable speed even as you load the motor. Or so I hope.

    Anyway, I’m done with this for now, but I’ll get back on it when new parts arrive.

  • @Ron_Ron

    The one I have is not ideal, but it is rated for 4kW, and 240VAC. I need 1800W at 90VDC on the output side for full throttle.

Log in to reply