Good morning. I have come into possession of several NEMA 17 steppers. There are no markings on the to tell me how to set the vRef. I there any way to tell what the proper vRef should be set to?
Thanks
Rich - K9WG
"NEMA 17" doesn't say much about the motor other than it's physical size. And that your drivers have a Vref doesn't tell us much about the your drivers.
What are you looking for? Some dude on the internet to say: "Vref = 0.1V...definitely!"
I think you'll have to experiment to see what works with your unknown application. I'd start out low, with unloaded steppers, and see what the minimum is to make them turn. As far as a maximum, many NEMA17 can operate at scaldingly hot temperatures.
The driver is a A4988. The steppers have no marking at all, just the four leads to go to the driver board. Is there some guide as to how much current vs. coil resistance or the like?
With the resistance of the coils and the size of the motor (not only the mounting plate), I'm sure you can search through stepper tables to find a match for your motor.
Leo..
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The A4988 can handle at most 1 Ampere per coil. You will need the manufacturer's rating to know how much the motor can tolerate.
How big are the steppers?
Here's a table from McMaster Carr:
And the A4988s can have different sense resistors. Are they marked 050? 068? R10?
From what I've seen, I'd try:
Vref = Imax*8*Rs = 0.1*8*0.05 = 0.4V
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Thanks all for the replies.
The motors I have are 47mm body length with a 24mm shaft. The coils measure 3 ohms. I have set it up to 0.2V and am letting it run for awhile to see how hot it gets. Once again thanks for directing me in the right direction.
Rich - K9WG
Industrial steppers are rated to run for long periods of time at up to 80 C case temperature, (50 C above ambient), which seems very hot to touch, but not damaging to the motor.
Since the A4988 can support at most 1A/winding steady state, that is 6 W total for 2x3 Ohm windings and unlikely to create a problem.
To make sense of Vref, you need to know the value of the current sense resistors on your particular A4988 module.
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Did you subtract the error of the leads of your DMM.
That size has about 5watt coils, which calculates to between 1.5 and 2A. The A4988, set to 1A, will work. The DRV8825 could be a better choice if you want performance.
Leo..
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