I recently found a Permanent Magnet 90vdc motor, 2.5hp, 18Amps. It has simply two wires for voltage (red/black) and two for thermal breaker circuit i believe (blue/blue). It came out of an old treadmill, and was run with an MC-60 motor control board. The problem is, the controller is shot and I really don't feel like wasting a ton of time analyzing what could be wrong with that old circuit being that I don't have the equipment here at home.

My Intent:

To build as simple of a control circuit as possible, giving me basic on/off and a fair amount of speed control. Once I have the speed control I'm looking for I'm going to gear it down to provide a more consistent speed/torque to drive a pottery wheel. If I have to I might get into the whole op-amp/servo-loop for consistent speeds but hoping gearing and flywheel will help with possible speed changes due to weight/load.

Can I use something as simple as the simple 555/mosfet circuit below, obviously scaling up the bridge and mosfet to handle ~30-40 amps or so? Simple 555 & Mosfet controller

Or should I try to isolate the power supply circuitry from the original circuit, and drive it through the opto via something like my netduino? Thus eliminating all the SoftStart/CurrentLimit/Signal circuitry that is just not necessary to me at this point. Original MC-60 Circuit

I'd love to hear any criticism/references/possible solutions.

Before you worry too much about giving advice, I do have a good amount of experience with both AC mains and digital electronics. I was a carpenter wiring breaker boxes for 5 years, and now currently build/repair circuits. Where I'm coming short is understanding how to safely connect/isolate the two and drive such a large motor. I've handled smaller ~12v motors but nothing like this. Plus I'm actually testing all of my circuits digitally via MultiSim prior to actually building anything, because I know this isn't one of those "well lets see what this does" type of situations. I'd like to not fry my motor, and keep my eyebrows. :)

Thanks in advance!

  • \$\begingroup\$ Ultimately, are you wanting a constant speed solution for your wheel? You mentioned "fair amount of speed control" but I have a small suspicion that ultimately you want constant speed. Tell me I'm wrong! \$\endgroup\$
    – Andy aka
    Commented Sep 14, 2013 at 23:38
  • \$\begingroup\$ @Andyaka Well I want constant speed at any given speed, but would like to at least adjust between low-med-high speed? That's what I mean. Thanks for speedy reply btw. \$\endgroup\$
    – While-E
    Commented Sep 15, 2013 at 0:20
  • \$\begingroup\$ Do you think you'll need to use the full 2.5hp. I'm thinking if you can run it at 30V you may get a good deal of power from it still and there are a gazillion more circuits available on line. Getting the FETs at the voltage and current is going to be costly. \$\endgroup\$
    – Andy aka
    Commented Sep 15, 2013 at 15:41
  • 1
    \$\begingroup\$ You may want to check your motor's information. A motor rated at 2.5 hp @ 90 VDC will draw about 20.7 Amps assuming 100% efficiency. Probably closer to 25 Amps assuming an 85-90% efficiency. So that 18 Amps that you mention can't be right (or the 2.5 hp isn't right). \$\endgroup\$
    – Eric
    Commented Sep 17, 2013 at 21:09
  • \$\begingroup\$ What are you using for speed and position feedback \$\endgroup\$
    – user16222
    Commented Jan 26, 2014 at 19:57

1 Answer 1


I am in the same situation I found this guy that could have some clues



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