Bipolar drive of unipolar stepper motor?

AFAIK, yes, you can.

To avoid overheating the motor you'd need to drive it at sqrt(2) of the unipolar drive voltage, so you'll only increase torque by 40% rather than doubling it. Depending on how the motor is designed you may or may not have funny saturation problems. Of course you can always run the motor at the unipolar current for double the power dissipation in the motor -- if it's intermittent use you may even be able to get away with it.

I've never done this myself, so I can't lend anything more than some ramblings based on theory.

Actually, it's pretty low end for serious motion control.

Yes. This is quite common. One catch through is that you increase the inductance, and for this reason you may want a higher power supply voltage to supply your chop-mode current regulator if you need high step rates. Good motors may be 8 wire so that you can run the half windings in parallel rather than series (using high current drivers of course).

Not necessarily. With a good driver the limiations may actually be either heat dissipation in the motor, or the field strength at which you risk demagnetizing the permanent magnets in the motor. (BTW, don't ever pull the rotor out of a stepper motor without using a flux keeper sleeve)

Try asking on alt.machines.cnc or the yahoo group CAD_CAM_EDM_DRO - the hobbyist CNC gang does a lot with stepper motors from those using L298 type drivers up to ones using discrete H bridges of N MOSFETs with floating high-side date drivers, etc.

A Schleuniger?

Yes. Maybe a NEMA 34 frame, depending on how big your fist is.

Old-fashioned bipolar dual H-bridge design, gets really hot with substantial current. ST makes them, Mouser and Digikey should carry replacements if it's shot. It's only switchmode if you drive it so (eg. with the sidekick sequencer chip).

That's fine.

Yes, you can use the unipolar as a bipolar by ignoring the center taps on each coil and driving the ends with an H-bridge.

Yes, but you are getting twice the heating with two coils energized. Not sure the relationship is between torque and driving method, but motor data sheets should have this information.

Best regards, Spehro Pefhany

Unit is a Schuleniger UC 3750 and will be up for sale once I complete the refurb.

Presumably the original engineering with regard to heat and current etc... will still be valid once I replace the driver. I'm just trying to find out exactly what they were intending to do.

Besides being frozen and locked up (already repaired with new bushings, etc), some junior G-Man plant electrician managed to replace a bridge rectifier 180 degrees out of position, thus converting the +42 volt supply to a MINUS 42 volt supply, and raising all holy hell in the process.

Most of the refurb is done. Blades appear perfect and rollers repolished beautifully. I suspect the slightly smaller rollers might affect the exact wire size programmed in, though.

Discovered after a dozen false starts that the way you replace an oilite bushing is to use a Hex Allen Cap Screw! Between the 20 threads per inch and another 18:1 or so of wrench gain, two or three pounds of twist gives you half a ton of insertion/withdrawal force.

Sure has been an adventure restoring an obvious basket case. Also willing to sell as is at 90 percent refurbed.

For unknown 6 wire stepper motors,I temporarely glue a stick to the shaft, then touch a mall voltage to each of the four coil ends. the stick moves a bit for each ending, and it shows you the order in which to step them(watch out for bouncing across whole step(s)). to control the motor then ,the centre taps go to the supply, and you step through the four endings in succesion. I get a higher momentum when i step (a+b b+c c+d d+a .......), watch motor temperature when you do that(but the holding torque is very high).

Alnico???

Thought that stuff hasn't been used for ages.

Tim

-- Deep Fryer: a very philosophical monk. Website: