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Author Topic: High Voltage Unipolar Stepper Driver  (Read 2980 times)

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High Voltage Unipolar Stepper Driver
« on: October 08, 2008, 12:20:04 PM »
I have a bunch of 8V nema 34 motors.  I'm thinking about a circuit: ac to fuse to bridge-rectifier to capacitors to get apprx 160V dc for a unipolar driver that uses TIP 50s and a L297 chopper/controller.  Am I nuts(?)  Cheap parts, should make em go... anybody tried this? Any suggestions?

Offline jimpinder

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Re: High Voltage Unipolar Stepper Driver
« Reply #1 on: October 09, 2008, 12:24:46 PM »
I don't really understand the question -

1. Why 160 v - it is normal to run steppers about 4 to 5 times more that then rated voltage - so for you 40 volts.
2. Have you got driver cards for these motors - if so what is their rated voltage _ the motors don't really matter.

Yes - I can build a 4 pole microprocessor controlled stepper motor driver - but the output from Mach requires one that responds to step and dircetion pulses, and you seem to be a long way from that.
Not me driving the engine - I'm better looking.
Re: High Voltage Unipolar Stepper Driver
« Reply #2 on: October 09, 2008, 12:44:04 PM »
I'm building the drivers.  The L297 uses step and direction inputs.
I guess the question is two-fold:  Is there any significant performance increase to be had from the higher voltage (160V vrs 46V)?   
Any pitfalls (don't tase me bro!)?   This would be a very inexpensive power supply.  The motors are rated at 0.83A, so
devices that can switch this voltage are pretty cheap too.

Offline jimpinder

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Re: High Voltage Unipolar Stepper Driver
« Reply #3 on: October 09, 2008, 01:00:30 PM »
Going to 160 volts is way over the top. Steppers motors start and stop each step, and there are (usually) 200 steps per revolution. To get better performance out of them it is normal to use about 5 times the rated voltage - which "encourages" them to accelerate faster, without burning them out.

I misread your first post, and you do not say what voltage the 0.83 amps is applicable to - there must be one.

Try testing across one of your coils and see what resistance the coil is. This will give you some idea. E = IR and all that. I would use about 5 times the rated voltage - any more and you then stand the risk of burning out the motor - not when it is moving - but when it is stood, because unless you build into the circuit some sort of current limiter, since steppers still have current going through their coils when stood, this is when melt down will occur. At 160 volts I would have thought that to be fairly soon.
Not me driving the engine - I'm better looking.
Re: High Voltage Unipolar Stepper Driver
« Reply #4 on: October 09, 2008, 01:14:18 PM »
The L297 has a current sensing/limiting chopper that will be used to limit the current to 0.83A.

Offline jimpinder

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Re: High Voltage Unipolar Stepper Driver
« Reply #5 on: October 09, 2008, 03:05:21 PM »
It will need it ;D ;D :'(
Not me driving the engine - I'm better looking.