Can someone help me with specifications for a stepper?

I'm thinking about building a CNC machine of some kind, probably just a simple X-Y plotter to start with.

I found I have 3 old stepper motors I pulled from a printer years ago. Only two look suitable but unfortunately one of those only lists resistance and step angle, nothing else.


It's a Sanyo Denki 103-557-0242 of 11.5 Ohm and 1.875 Degree/Step.

Unfortunately the equipment it was in is long since gone so I can't plug it back in and measure or anything.

Interestingly though I found reference to one here: [forums.reprap.org] - but no mention of voltage etc.


Can anyone help, or is there a way I can test and find out what the voltage is likely to be?

I also found here: [detail.china.alibaba.com] they say 24v 1A but I am not sure how accurate that description would be, since the same number is listed along these: [detail.china.alibaba.com] but says 12v 2A.

11.5 ohms means 12V / 11.5 ohms = 1.04A. The voltage given on steppers isn't that important, they can all handle some 50 volts or more.

Stepper drivers have a current limit built in, so if you supply them with more than the specified voltage, this limit kicks in. And you want this limit to kick in to maintain current, and thus tourque, at higher RPM. Turning a motor will result in a counter-voltage produced by the motor, the higher the RPM, the higher this counter-voltage. If this motor runs fast enough to produce 5V counter-voltage, you'd get (12V - 5V) / 11.5 ohms = 0.6 amps, resulting in only 60% of the nominal tourque.

Important is, wether the motor is bipolar or unipolar. As your motors are 6-wire, it's bipolar and can be used with Pololu-like stepper drivers. Just don't expect too much tourque at high speeds, as you can maintain this 1 amps for very slow movements, only.

A way to get tourque at higher speeds would require a higher voltage supply, like 24V.

Did you read the wiki already? [reprap.org]

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Traumflug Wrote:
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> 11.5 ohms means 12V / 11.5 ohms = 1.04A. The
> voltage given on steppers isn't that important,
> they can all handle some 50 volts or more.

I did not know that at all. Another motor I have says 3.9v on it (totally different brand\model) so I thought that they would all have different maximum ratings quite lower than 50v like a 'standard' motor.

Guess when I thought I knew how stepper motors worked, I was wrong!

> Did you read the wiki already?
> [reprap.org]

No, I didn't see that. Reading that looks like a very good idea... thanks for the advice