Stepper motor testing

If you take a 4 bit shift register, clock one bit around in it, connect the 3rd bit to the input,and attatch 3 bits with a 1-3 ampere darlington transistor to the 3 coils, and the common to something like 5 or 12 volt supply, shift the register with something like 5 hz(or use a pushbutton), you have a nice tester. Swap two coil wires to reverse direction. Oh and put 1 amp diodes across the coils to keep your transistors from breaking down.

what tests do you want to do?

I've used aligator clips in the past.

Hi, Russ. Use a few switches and manually go through the steps. Does that make sense?

Cheers Chris

Use a meter to determine each coil resistance. They should be close. Then tap 5 volts across once coil, feel the shaft, it should bump once for each tap. The other coil should do the same thing.

sure, connect some AC to it. it'll move...

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I just want to see if it works. When I find them on the equipment I sometimes have to guess if it is the motor or the driver pcb. Both are expensive so I just want to take the motor and test it with a something and watch it spin around.

s

This sounds easy but is it through. Sometimes I find a stepper motor in the equipment that just kind of vibrates back and forth. Do you think the switches would catch this kind of thing?

r

I was checking a few and found one coil with the resistance down from

5.3 ohms to 2.6 ohms. Is this enough to cause a problem? If one coil is off by a few ohms this could cause the thing not to spin correctly I would think. Because of the costs of the motor, driver pcb and down time I hope I can find something that can tell me almost for sure that it is good or bad. I guess I will have to experiment a little. Thank you, Russ

Are you sure about that...

Thanks I guess this is the answer. You don't think there will be a problem using different motors with different resistance or number of coils?

Yes, I'm sure about that.

The amount of AC depends on the motor voltage rating.

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Greetings Russ, Stepper motors, at least the kind you are likely to find, e.g., in a printer or disc drive, will have 4 coils. If there are 5 wires coming out of the stepper then the coils will be connected in pairs giving you in effect two center tapped coils. So, if you measure from the center tap to one end of the coil the resistance will be 1/2 of what you would get if you measured the resistance across the ends. Which is just what you measured. The rotor has teeth on it that line up with the coils as they are energized. That is why just applying DC power to any pair of wires won't make the motor spin. The coils must be turned on and off in sequence to make the thing spin. This is what makes stepper motors so useful. They are used to position the shaft by stepping the motor the desired number of steps and no position feedback is needed. If you can spin the shaft with your fingers then you can test the motor by applying DC to a pair of wires and feeling the change in the torque required to spin the shaft manually compared to when the power is removed. If there is no change then that coil is bad. Unlikely though to find a bad stepper. As you apply power to different pairs of wires the motor shaft should step, apply power in the correct sequence and the shaft will step in one direction instead of stepping back and forth. ERS

No. Just find the common connection of the coils, and for the number of coils, make the shift register the same length of bits. Most are 4 coils, and have a 5 pin connector, but 3 coils is also possible. My first message talked about 3 coils.

You need to switch four wires in a phased way; two ways to do this, are a clocked circuit, and a manual switched driver.

For the clocked circuit, feed an oscillator into two D flip/flops, D1 (Din input of flip/flop # 1) connected to Q2, and D2 connected to /Q1 (that's the inverted output of flip/flop 1). Power is applied from a bench supply through a limit resistor to the common point, and transistor or MOSFET switches driven from Q1 and /Q1 drive one coil winding while switches from Q2 and /Q2 drive the other winding.

And, of course, a four-position make-before-break rotary switch with two wafers (DP4T) can be connected to do the same thing as all the clocks and transistors. A 15 degree stepper will complete one revolution when the switch is cranked through

24 turns. Maybe it'd be easiest to use a cast-iron disk from an exercise weight set as your knob; spin it up!

Every old moving-ball mouse generates the right phases for running a stepper, too.