weird resistance on 5 wire stepper

[xinzc28]

I have stepper, it's 5 wire, let say wire: A B C D E

wire E is the center tap, it's resistance to A/B/C/D = 8ohm.
the weird thing is: resistance A to B/C/D = 16ohm!

what kind stepper do i have?
could it be a defective one?

[mechatronicsman]

Hi,
you probably have a five wire unipolar stepper, see image. (Common = your E, Coil 1-4 = your A-D) Each coil is 8 ohms.

When you measure between A to B/C/D you measure two of the coils in series, i.e. A to B (Coil 1 to Coil 2). Resistors in series adds together, 8+8ohms=16ohms. So this is perfectly normal. (Coil1 to coil2/3/4 on the image below).

(Image borrowed from http://www.doc.ic.ac.uk/~ih/doc/stepper/others/)

[xinzc28]

thanks for your info.

can I drive is as bipolar using bipolar controller?
I find some threads in the forum, driving 5 wire unipolar as bipolar will cause some error on positioning, is it true?

[irving2008]

Originally Posted by xinzc28 thanks for your info. can I drive is as bipolar using bipolar controller? I find some threads in the forum, driving 5 wire unipolar as bipolar will cause some error on positioning, is it true?

You will often find if you can open the motor up that the common wire is actually 2 wires. If you can split them you then have a 6-wire motor which can be driven either unipolar or bipolar series (but not bipolar parallel). Of course, if you can open the motor up you may be able to isolate all 4 windings and then get all modes of operation.

However many 5-wire motors are pretty light-weight and it may not be worth the trouble.