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I recently bought a CNC mini-mill at an auction. It is fitted with steppers on the three axis. The X and Y are the same, and the Z is a bit smaller (physically). All the markings were removed from the motors and they are painted flat black. Yet another reason to hate proprietary hardware :-) The machine was originally designed to use a custom controller which is missing.

My question is, can I figure out what voltage the motors were intended to run at? Does the coil resistance offer any clues? I have a good quality multi-meter, and I have already reverse engineered the wiring. I don't want to fry the motors though.

Thanks for any advice!

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2 Answers

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If you use a good driver circuit that has current limiting and chopper features, it really won't matter. Basically you can slowly crank up the current on these drivers while checking the stepper motor temperature and usually you can operate them at a voltage MUCH higher then they were intended with the right circuit. I am currently in a CNC build project and I am about to do that very thing. You can follow me on my Blog. WWW.MENDINGTHINGS.COM

Good luck.

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I like this suggestion but I think it represents a "plan B". I would rather figure out the actual specs (or as close as possible). – jkopel Feb 17 at 3:09
I understand. I was going to do this anyway so I set up a test and posted a video on my blog. This is actually done very often in industrial applications. However if you don't use a stepper driver with chopper features then all bets are off. As for the driver needing to be oversized, I think you can see the little EasyDriver that is rated at 750MA is not straining at all and for $15 you can't beat it. Good luck with your project. – Mark B Feb 18 at 3:46
I forgot to mention that I am betting your steppers are much larger and you would most likely need a larger driver than this but maybe not. – Mark B Feb 18 at 3:53
Nice post Mark, and thanks! My steppers are quite a bit larger then the ones you are using, but I am going to get one of the EasyDriver boards and give it a try. – jkopel Feb 21 at 18:19
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The total weight of the motor and the coil resistance might be a good guide. See if you can find some specs on the web and match them to your motor. I have done similiar things with rechargeable batteries matching chemistry and weight. I also think that Mark B's advice is pretty good, but suggests an over sized driver.

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