Stepper motor driving- Unipolar Vs Bipolar

When you energize a coil in a unipolar motor, that's 25% of the motor, but when you energize a coil on a bipolar motor, that's 50% of the motor, so yes, you get more output.

Reply to
Bryan Hackney
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Hi

Is it true that driving using bipolar method will provide more torque for most motors as compared to unipolar method?

Thanks Richard

Reply to
Richard

Yes. A bipolar drive benefits from less winding resistance and can give upto 40% more torque.

Reply to
John Jardine

...for the same copper losses.

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John Popelish
Reply to
John Popelish

40%

Argghhh, Copper losses ... John . You're well au fait with the steppers. Any morsels you can cast in my direction? ... I finished a unipolar chopper design last month (1/2 to 6amps). Ran tests on a collection of (11) motors and noticed they -all- overheat. This time round I used a real temp' probe as against the usual spit and was surprised to see temps of 90deg+ (and rising). The makers usually specify a max case temp rise of 55degC over ambient. This seems only qualifiable when a single motor coil is fed with the rated voltage and -not- the rated current (=spiralling I^2.R loss due to +3900ppm wire tempco). I've got no sense out of makers as to how they actually do their motor temp' rating tests. Is there some kind of 'industry standard constant-current derating factor', I've missed?. (I'm worried that I can't in honesty say to a customer "this chopper will drive a motor at it's rated current", knowing it could blow smoke if they do so :-). regards john

Reply to
John Jardine

Losses in stepper motors depend a lot on the details of the driving circuit (pwm frequency, peak voltage, spike clamping, as well as average current.)

I seldom run any stepper at its full rated current. If I really need the full rated torque, I prefer to move up a frame size to keep the temperature under control.

Can you send me a copy of your schematic. I might be able to suggest some efficiency improving changes. But as a generality, using only half a winding at a time is not the way to keep temperature rise low.

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John Popelish
Reply to
John Popelish

You may have met the other major loss: eddy and hysteresis losses in the iron of the motor. For a fast PWM, you may get an advantage over the high-frequency losses by using external filter chokes with core material and structure fit to the chopper speed.

HTH

Tauno Voipio tauno voipio @ iki fi

Reply to
Tauno Voipio

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