Hi All

I starting playing around with some stepper motors and have a few questions:

Some info:
The steppers are from OKI 521 Microline printers, and on the motor casing the motor ratings are: 6.2V, 7.5deg Steps. It is a 4 wire bipolar motor and each coil measures 10Ω (The printer service manual says it should be 13Ω, which I think might be after the motor warms up?).

According to ohms law the current throught the motor @ 6.2V/13Ω=0.47A.

1) Would it be safe to assume the motor can take 0.47A @ 6.2V?

From the service manual and measurements it looks like the OKI motor driver puts out 40V on each coil without the motor connected, but only 2V when the motor is connected.

2) Is the V drop measured because the motor driver is "chopping" the supply to limit the amps going to the motor?

When I connect my amp meter to the OKI motor driver output (it is a direct connection, not clamp on meter, without the motor connected) it measures 0.128A. With the motor connected to the motor driver in series with the amp meter it also measures 0.128A. Both these measurements are with the motor stationary.

I am going to use a L297/L298 motor driver, so

3) Would it be safe (and the optimal setting) if I run the motor from a 40V supply and set the current limit on the L298 to 0.128A?

Thanks,
Darius

In order to enhance performance (both power and speed) it's normal to run steppers at a MUCH higher voltage, and limit the current - a large wirewound ressitor is the common way, although PWM is popular now as well.