Find Bipolar Stepper Motor Coil Pairs




About: My name is Randy and I am a Community Manager in these here parts. In a previous life I had founded and run the Instructables Design Studio (RIP) @ Autodesk's Pier 9 Technology Center. I'm also the author ...

There is a really easy way to figure out which two sets of wired are paired on a bipolar stepper motor. Get an LED, and hold the anode and cathode to any of the motor's two electrical connections (respectively). Turn the motor shaft and see if it lights up. If it does not light up, change where the wires are connected and try again. Keep changing these pairs until one set lights up.

Once you have found a pair that lights the LED, it is fair to assume that the other pair of wires are also connected, and will also light an LED. You now have found and identified the coil pairs and can start working with the motor.

If the LED does not light up with any pairs, you can get a similar result by using a multimeter and measuring the voltage that the motor outputs when you turn the shaft.



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    12 Discussions


    4 years ago on Introduction

    If you don't have a LED handy (unlikely, but it happens) here's another trick:

    Turn the shaft and note how hard it is to turn it.

    Now just short to wires at random and try to turn the shaft.

    If it turns as easily as before then try another pair until you find the pair that when shorted makes turning the shaft harder. That's your bipolar pair.


    5 years ago on Introduction

    Nice instructable. Thanks. I use steppers from time to time and have found this useful.


    6 years ago on Introduction

    As it does not hurt the stepper if it's wrong, then plug it in at random- ABCD

    If it does not work, then change the last 2 with each other. ABDC

    If that does not do the trick, then leave it as is, but change the middle 2 with each other. ADBC

    Thats it.

    If wrong rotation direction then mirror them so abcd becomes dcba

    1 reply

    6 years ago on Introduction

    Does the LED light no matter which polarity it is and which way you spin the motor shaft? It might due to back EMF. If you have a multimeter why not just use it on the ohms scale? No spinning required then. If you don't have a multimeter what are you doing playing with a stepper motor?

    My favorite thing is to hook two stepper motors up coil to coil, then spin the shaft of one, and watch the other go around. Magic! Good way to make sure both of your motors are OK too. I'm sure there is some way of phase testing an unknown stepper motor doing that if you know the wiring of one of them.

    You can write that article randofo. Or just freak out your co-workers with the magic of a stepper motor being a stepper motor driver if you manually spin it.

    5 replies

    Reply 6 years ago on Introduction

    I didn't discover it, I read about it, and I know it has been used for some strange mechanical linkage deals in the past. It is like a magic trick though, especially to people who "know" about electricity, and electronics. It just seems to work too well. Better than I'd have given it credit for working before I did it for myself.


    Reply 6 years ago on Introduction

    Lights up no matter which way you orient it. Learned this from someone who was doing research to use them as small-scale power generators. Always thought this was a clever trick. LEDs will light up with almost all motors of this type.


    Reply 6 years ago on Introduction

    Then it lights on one phase of the current. Either the forward, or the back EMF, depending on the lamp orientation. Because LEDs are polarized devices. Now I wonder if there is a way to combine 2 to figure out the motor phase?

    Darn... I thought you had invented a device to help with bipolar disorder, a rotten mental illness-I speak from personal experience. Your invention is very cool though! Thanks for sharing :0)

    Neat trick ! The LED will light in either orentation because the stepper motor is acting as an alternator, putting out AC. This is great example of working with what is at hand !! GOOD SHOW.