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YES...!! (Sorry for the delay, I had a few other projects working.)

8.04 is now running. That saves me a lot of heartburn because I have several systems that I'm starting up and I didn't want to buy more PC's.

Now I'm on to the next problem. My steppers are 1.4V and the controller board (HY-TB3DV-M) specifies 12V minimum for the motors. I'll post elsewhere for this one.

Thanks ArcEye and BigJohnT..!!

-JBottoms
Concord, MA

Step motors are current operated devices with high inductance which means they need higher voltage supplied to change the current than when stopped. That is, the 1.4V rating is a DC rating (voltage for full current when the step motor is stopped).

To move the stepmotor, you need to apply AC voltages to the coils with a frequency that varies with the step rate. Because of the step motor coil inductance the higher the steprate, the higher the voltage you need to get the same current. Step drives accommodate this characteristic by effectively varying the motor voltage depending on the speed (simple drives do this via sensing the motor current and "chopping" the applied voltage)

So to actually run the stepmotor you need much more voltage than the 1.4v
typically step drives have a 20-50x motor voltage power supply

PCW,

Thanks, I think I understand the basics. What I would like to do is control the motors with a a TB6560 controller at 5 Volts rather than the recommended 12-36 Volts.

It seems that if the current is right (1.3A) and the voltage is right (1.4V) on the motor then the controller shouldn't care. This assumes that the voltages are above the silicon threshold. I think it's something like 1.3 Volts. Any reason why this wouldn't work?

Tnx

Agreed,

I don't understand the basics. It just seems intuitive that if the motor is rated at 1.4V and I supply it 1.4 volts it should operate as specified.
From Wikipedia: "However, it is winding current, not voltage that applies torque to the stepper motor shaft. "

What am I missing? Is the problem that the controller is not a perfect current source?

And I also found this at the same page: "The rated voltage will produce the rated winding current at DC: but this is mostly a meaningless rating, as all modern drivers are current limiting and the drive voltages greatly exceed the motor rated voltage."

It sounds like the stepper voltage can be ignored as long as the current requirement is satisfied. If that is the case could it be satisfied using 5V?

The problem is that the current requirement _cannot_ be satisfied with 5V once the step motor is moving at a decent speed so the torque will drop off very quickly. At Andy's 150 RPM example the two motor phases now have 125 Hz AC waveforms (sine waves in a perfect drive) instead of DC

At DC the current is determined entirely by the wire resistance (about 1 Ohm in your case) and 1.4V is enough but with the motor in motion and with AC signals two other things come into play. One is that the inductive reactance of the motor at the AC drive frequency makes the total motor impedance higher than the ~1 Ohm DC resistance so for example with a 10 mH motor winding inductance at 125 Hz you now have a ~8 Ohm impedance so you need ~10V now to get your 1.3A through the winding.

But wait, it gets worse... In addition to the motor inductance, the step motor acts as a generator when it is moving. The voltage it generates opposes the applied voltage so you need to supply enough AC voltage to counteract the inductance but also oppose the motors generated voltage (Back EMF)

This is why some high performance step drives for 2-4V motors are line operated (165VDC)!

Thanks PCW,

Excellent reply..!! I interpret this to mean the constant current source is not (welcome to the real world).

So, now, given that my motor is allegedly 1.4V, 1.3A, what is the recommended supply current. The TB6560 is rated at 12 - 36 Volts I believe. And how is the current limiting resistor selected?

Speed is not real important and I was looking at a lower voltage to reduce the losses in the current limiting resistor.

I'll be using "Morgan's recommended configuration" or something similar.