Hallo!

I've found documentation of mitsumi stepping motor here http://www.mitsumi.co.jp/Catalog/compo/motor/m42sp/6nk/text01e.pdf

They write that rated voltage U=12 V, rated current I=400 mA and coil resistance R=5 Ohm.

Ohm rule says R=U/I, so if i connect 12V to 5Ohm coil there should be 2,4A current. So why they write there that it should be 0,4A?

Thanks for any help
Konrad Gagor

 

The 12v spec just means that 12v is a "usual" driving voltage. It does not mean that you can apply 12v indefinitely without damaging the motor. High-performance stepper motor drivers control the current, not the voltage. They use PWM acting with the inductance of the motor to limit the current to a safe value. In this case, it is 0.4 (average) Amps. If you apply 12v without PWM you will draw 2.4 Amps and burn out the motor. If performance is not critical, then add some series resistance to make the current 0.4 Amps when voltage is applied.

Robert Scott
Real-Time Specialties
Embedded Systems Consulting