# Stepper motor phases

Discussion in 'Electronic Design' started by news.earthlink.net, Nov 20, 2004.

I have a lot of small stepper motors with 16 leads (8 pair of windings). Is
there some procedure I can go through to find the phase order of the
windings. I mean, I need to apply power to these windings, in order, so that
the motor will move in the most efficient manner. I tried an oscilloscope on
one set of leads while generating a sinusoidal signal on another but the
difference in inducted voltage was not enough to tell me which set of leads
was closest to the one into which I was generating the signal.

2. ### Dave GarnettGuest

Put a long pointer on the stepper shaft, and then energise each coil in
turn, noting where the pointer moves to ...

Dave

3. ### John LarkinGuest

Are there really 8 windings? Isolated and all the same resistance?
That's unusual. Might some be an encoder or something?

If it's a PM stepper (you should feel distinct detents if so) you
could spin the shaft (with a drill moror or something) and look at the
phase relationships of the voltages that come out, using a scope
maybe.

John

4. ### Larry BrasfieldGuest

I take it you mean there are 8 windings. That is very unusual
for stepper motors.
It is also quite possible that pairs of winding pairs share the
same magnetic circuit. The most likely reason for so many
winding is to allow series or parallel combinations for use
with different voltages and to allow unipolar or bipolar drive.
I would put one o'scope probe on an arbitrary winding
and trigger on its channel, then, while manually spinning
the rotor, observe the phase of the other windings with
another channel. You will probably observe 4 distinct
phases, or 2 if you eliminate opposing polarities. If that
is so, you have an ordinary stepper with a flexible
winding arrangement.