Overdriving a stepper motor

[RChadwick]

I've got a Sherline mill. It came with Vexta 12V, .68A motors. I'm using 3 linistepper boards. The motors just don't have enough torque. I was running them at 1A (Default config for the Linistepper kit) with a 24V supply, and they were passable, but started skipping steps at high speed (Around 100 RPM). I got a 36V power supply, and cranked it down to 32V, and things work great, except the motors get too hot to touch in about 20 minutes.

I'm going to experiment with voltages (Hard to do, my bench PS can't supply the needed current), hoping to find a point where it's usable, and doesn't get too hot. I'm basically looking for advice and comments. Would heat sinks on the motors be a good idea? Something else? I'm trying to avoid the obvious idea of replacing the motors. Thanks!

[highspeedmazak]

Replace the motors. I know you dont want to hear it but it is not that expensive for the problems you will save yourself from going through.

[RChadwick]

What problems? Burning out motors I'd toss out anyway if I replaced them?

My choices are:
1) Toss the motors, buy new ones, fit them to the mill, tweak and play.

2) Overdrive the existing motors. If it fails, then I do #1.

I want to start with #2. I have nothing to lose. Has anyone successfully overdriven their motors?

[James Newton]

I think you are going to find dimminishing returns... As the motors get hotter, they loose power (magnets do not like heat) and your motors are already being driven past thier limits (1A vs .68A) so there really isn't going to be any improvement. Usually the Linistepper will keep a motor running cool (because it doesn't generate eddy current and other AC losses in the motor coils) but when you put almost double the rated current through a motor, it's going to get hot.

If one of those coil wires melts in the motor and causes a sudden open, it may kill the power transistor on the Linistepper, leading to more repair work than just replacing the motor.

You might try heatsinks, or fins, and possibly a fan to cool down the motors, but replacement is the way to go.

Is it all three motors? Or is it just the main one? You might be able to replace just one motor, or one at a time and get by with the others.

The Linistepper is perfectly matched to used, older, unipolar stepper motors. Especially the sort you can pull from old laser printers (find a dead HP LJ II, III, or 4) or medium to large size copiers. Dot matrix printers are ok if they are the bigger ones, but the little guys are pretty useless. Don't bother with FAX machines. HP LaserJets are the best: The older the better; they don't make 'em like they used to.

Post a "WANTED" on your local freecycle list and you could end up with a nice set of high power motors along with a "thank you" for helping someone get rid of thier old junk. Urm... word to the wise; if you do pick up an old bit of electronics from someone, open it outside and be ready with a can of RAID or orange oil. Don't ask me how I know this...

[RChadwick]

Thanks for food for thought