Author Options:

A simple controller for a dc treadmill motor? Answered

I have a United Technologies dc motor, 2.5 hp @ 120VDC, but no controller.  It has a red & black wire, plus 2 blue wires.  The black goes through a choke coil.  Anybody have a breadboard type of design for a speed controller with hookup instructions?  I can solder, follow a schematic, and  wire a house, but  am not up on electronics.  Last radio I built was in the mid 50's, so I probably need more than usual specifics.  Thanks for any help you can offer.  Ed B


When you turn the motor, does it index like a permanent magnet motor?  Or is the rotation smooth like an a/c motor is.

If the rotation is smooth then the blue wires are probably to the field coil and the others are to the armature.

The motor turns smoothly.  It has a pretty good sized flywheel on it.  My plans are to use it  on my pig rotissierie.  Currently (& for the past 25 yrs) I've been using an old 1/4 horse ac motor, with a lot of gear reduction.  So what do I do with the blue wires?  Just looked closely at the back end and the black and red are indeed attached to the brushes.  When I hook them to AC, the thing turns very slowly and vibrates like heck.  BTW, I have a VARIAC, which controls AC voltage.  Would that be useful as a component if I ever get to build a speed controller of some kind?   Thanks for your interest.  Ed B

The blue wires should be connected to power.  I don't know if it should be ac or dc though.  They are what create the stationary magnet.  They replace the permanent magnet.

No, The blue wires are a thermal limit switch. They are to be wired in series with the AC hot wire like a switch.

If the motor gets too hot, the circuit will open.

There's an instructable on how to use treadmill motors and their controllers

What you want is a motor speed controller that uses Pulse Width Modulation.
A common motor speed controller found in many treadmills is the MC-60.
They  sell on EBAY for $30 and up.

I think the blue wires are for a thermal protector inside the motor.The thermal protector is wired in series with the 120V AC input to the  motor controller.

Thanks.  I'm going to look into E-Bay to see if I can find that MC-60 or something like it.  Matter of fact, I did read the instructable that you cite.  My problem was probably that it was a bit too general for my limited knowledge of the workings of these things.  One of the schematics that was shown seemed like it probably came from the same set up mine is from.  But that one seemed to have integrated in it some other circuitry for a lift motor and other things.  I had in mind something that I could connect all the wires to, plug into an AC socket and then turn a pot knob of some sort to vary the speed.  Ed B

DId you get your dc motor hooked up and working right. I have 2 such motors I plan to use on a power feed lathe. They are 24dcv but work on 12dcv just find. I don't want to reinvent the wheel just get the things to have speed control. What did you come up with?

You would need a variable voltage regulator circuit:


basically that, but with a much more beefy regulator

Did you miss the "120V" bit ? 

I'm not sure why it has four wires ? Is it Brushless ? Is it separately excited ? Does it have a tachogenerator on it ? 


It has brushes. (see my reply to Re-design)  Don't know what a tachogenerator is, but there is nothing attached on the outside.  I might just take off the end with the brushes and see if I can tell where the blue wires go.  I they go to the field coil like Re-design says they might, then I just have to figure out what their purpose is and what do I do with them.

See if you get the sense of any magnets in the thing, then its a PM motor and the black wires are the armature - maybe the blue wires are a thermal trip.


Yes, it's a permanent magnet motor.  I took off the brush end of the case and found that the blue wires are both attached to a small (approx. 3/8" x  3/4") flattish component which simply slips into a notched track on the perimeter of the cap which holds the brushes.  Could be a thermal trip.  As close as I can make out a tiny stamping on it says, Control Devices.

Off to Ebay then, to source the controller.

Those blue wires do sound suspiciously like some sort of tach.

when i come across stuff like that i just use red and black and ignore anything else and hope it works(and it usually does)

Still a nice thing to have at hand...who knows...you might find it worth something down the road (for instance, using the tach as a feedback source for a controller...)


if you use a different version of the regulator^one that accepts higher voltage^, you can control the speed.

That looks something like what I had envisioned.  Would the values of those components work for my motor?  The label says; 2.5HP@120VDC; 18Amps; 1700 RPM.

the circuit in the instructable provides 1.25-12v at 1.5 Amps

the LM317 can only put out 35v tops, at 1.5 amps, you will have to find a much more powerful voltage regulator to use