Speed controller problem for a Dayton DC Gearmotor

I just had some equipment fabricated to use a Dayton (Grainger) 1Z833 gearmotor and cannot change the form factor for the mount at this point.

The motor specifications are: 12VDC permanent magnet parallel shaft 1/6HP 14 amp and it is a brushed motor. The motor will have a light load and so I do not need full power and probably not full speed either.

I purchased two different motor speed controllers to try out so I can have computer control of the speed. One is the Pololu Jrk 12v12 USB Motor controller with Feedback (12A continuous, 30A peak). The other is a Dimension Engineering SyRen 25 (25A continuous, 45A peak).

When I looked into the motor manual, it had a statement that said "Dayton low voltage DC gearmotors operate on non-pulsating DC power or filtered full wave rectified power with a form factor not exceeding 1.05. Operation with power supplies providing a form factor above 1.05 must require a derate of gearmotor torque rating."

When I spoke with the Grainger technical support person, he did not have a clear explanation as to why a PWM motor controller should not be used. He mentioned such things as perhaps gear lash (which with a PWM at a high frequency does not make sense to me) and said that there must be some reason for the manufacturer's statement in the booklet. He claimed the motor controllers they sell use a series of SCRs and they maintain a constant 12V output and they modulate the current (which also does not make sense to me). Unfortunately, their controllers adjust speed using a potentiometer and I need computer control (either using a D/A output or serial connection).

I will only need to run the motor in one direction, do not need braking, and I can ramp the speed up and down if I have to but I would need to do that within about one second.

I should have read the fine print before, but I thought that one could use a DC motor controller on any brushed DC motor (but it’s too late now and I have to work with the equipment I have). Can I use either of the motor controllers I purchased or is there a real reason they should not be used? How should I proceed--is there another motor controller that would work for this application?

Thanks,
Dale

I believe the controllers would be ok to use. I agree with you, there seems to be no good reason that they won't work with that motor.

Also the Grainger support person's statement that their controller maintains a constant 12V while modulating the current also doesn't make sense, as you noted. To regulate current you have to regulate voltage.

I say give the controllers a try. I suspect they will work fine, especially since the motor will be running under a light load.

If you look in WW Graingers book or online when you buy a DC motor it lists recommended motor controllers. Look at the full load amp rating of the motor then check the amp rating of the controller. If the amp rating of the controller is lower than the motor it will not work correctly. Also the voltage needs to be rated for that motor. I have used a lot of Graingers gear motors one time grainger sent me the wrong controllers it looked the same as the photo in the book but amps were to low for that motor. Motor ran fine at low RPM but would not run right above about 1/2 throttle then if it got over loaded it would blow the fuse. What you have listed above it looks to me like they will both work.

I don't get the "form factor above 1.05" thing. How is that relevant to the controller type? What the heck is a power form factor anyway?

EDIT: Never mind, I think it was just part of the statement, andn not relevant to the type of control. As far as the statement from the Grainger guy, he probably meant that the recommended controller uses variable current to control the speed. In such a system, the voltage would be allowed to change to any value required to draw the prescribed current. PWM control does nearly the same thing, though in a more efficient manner. I don't know why it wouldn't work, but I'll think about it and post if I come up with anything.

i dont think its a problem to use the controllers you have, any how add a reverse diode at the terminals of the motor to make sure you dont breake the current suddenly at anytime.

Thanks everyone for your help and advice. Your comments seem a lot more reasonable than the advice I received from Grainger "tech support". I will try the motor controllers I purchased. Thanks again, Dale