Problem supplying stepper motor from 12V battery

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Hi!

I've got some problem supplying my 4-phase microcon.cz sx17-1705 stepper motor.
Resistance of a winding wired as unipolar is 1.2ohms, rated for current 1.7A per phase.(2V on motor) System voltage is determined by 12V(5Ah) battery. I was first thinking of voltage drive with series resistor in each phase. But it's 10V*1.7=17W. That's way too much for a resistor.

I see now only one possibilty- to buy a step down converter. MC34167 5A separate for each motor. Or something even bigger like http://cgi.ebay.com/DCDC-Convert... rated for 10A. Get it down to 5V and then use 5w resistors.

What would be good solutoin for this case?
Thanks

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One of the strategies in stepper system design is to rely on the inductance and PWM the winding at a high enough frequency that you never see the full V/R current. This makes the mechanical system a lot faster and gives it more torque. Further, you can now do microstepping.

The down-side to this is that you can never let it sit there, with power on, without also PWM. Depending on the nature of the load, static "cogging" may hold it in place when its not moving. But, if not, you will have to apply some power to hold it, and it will have to be PWM.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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You might want to look into using a dedicated stepper motor driver chip. The Allegro A3982 is one example. It has a built in PWM function to limit the motor current, which lets you use a much higher than needed drive voltage without wasting huge amounts of power.

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I agree on a dedicated driver chip. They can save big head ache problems!

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Or four 20W resistors.

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