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Stepper motor with no wiring diagram?

No problem... get some masking tape and a pen.

Eight wire motors:

Step 0: prep work

Note: you will be turning the motor shaft, which makes it act like a generator. If you hold the wire ends in your bare fingers, you might get a bit of a harmless tingle. If you don't like that, use gloves, or twist the ends together and don't touch them while turning the motor shaft.

Strip the ends of all eight leads. Make sure the ends don't touch each other, and try to give the shaft a spin. It should turn with only a little cogging. Remember what that amount of drag and cogging feels like.

Step 1: identify the windings

Now pick one wire - any one - and put a tape label on it that says "1". One at a time, connect a single unlabeled wire to "1" and try to turn the motor. Then disconnect that wire and go to the next one. Make sure no other wire ends get shorted together - you might want to put tape over the ends if they are being unruly.

One and only one wire should make it a lot harder to turn (with strong cogging) when connected to wire "1". Label that wire "2". Disconnect all wires, and tape the ends of 1 and 2 so they don't accidentally touch anything.

There are 6 unlabeled wires left. Label one of them "3". Again, connect one unlabeled wire at at time to "3". Only one of them should make the motor hard to turn, label it "4". Disconnect all wires and tape the ends of 3 and 4.

Four left... label one "5". One and only one of the other three should make it hard to turn when shorted to "5". That one is "6". Disconnect all wires.

Two left... nothing to do now but label them "7" and "8". (Doesn't matter which is which, we'll fix that later.)

First step is done, you have identified the four windings in the motor. They are 1-2, 3-4, 5-6, and 7-8.

Step 2: identify the phases

We still don't know anything about which windings are phase A and which ones are phase B, nor do we know the polarity. The next test will identify the phasing.

Connect 1 to 2, and wrap in tape to prevent accidental shorts. With the 1-2 winding shorted, the motor should be hard to turn, with much cogging. (If you can't turn it at all by hand, you'll need a wrench or something - for this part of the test you must be able to turn it.)

Now, leave 1 and 2 connected, and connect 3 to 4. Turn the shaft again. If there is still lots of cogging, maybe even more than when with 1-2 only connected, then 3-4 are in the same phase as 1-2, and the labels should stay as they are.

However, if the motor is hard to turn but much smoother, with only a little cogging, that says that 3-4 are NOT in the same phase as 1-2.

Disconnect 3 from 4. Connect 5 to 6, and try to turn the shaft. If it turns with much cogging, then 5-6 are the same phase as 1-2. If it turns hard but smooth, then 5-6 are NOT the same phase as 1-2.

Disconnect 5 from 6, Connect 7 to 8, and try to turn it. Lots of cogging means 7-8 are the same phase as 1-2, hard but smooth means 7-8 are the opposite phase.

After these three steps, you know which winding pairs up with 1-2. Its the one that causes lots of cogging when it is shorted at the same time as 1-2. If that winding is 3-4, you are done with this step. If it is 5-6, then switch labels between 5-6 and 3-4. If it is 7-8, switch labels between 7-8 and 3-4.

Now we have the four windings paired up into phases. 1-2 and 3-4 are the "A" phase, and 5-6 plus 7-8 are the "B" phase.

Step 3: polarity

The only thing left to figure out is polarity.

Make sure none of the wires are touching each other again (tape if needed). Then twist 2 and 3 together and tape them. You should be able to turn the motor easily. Now connect 1 and 4. If it is hard to turn, that means 1-2 and 3-4 are in series, and they are labeled correctly. If easy to turn then switch the labels on 3 and 4.

Disconnect everything again. Twist 6 and 7 together and tape them. The motor should turn easily. Now connect 5 and 8. If it is hard to turn, the labels are correct. If it is easy, swap the labels on 7 and 8.

Congradulations, you have identified all 8 wires on your motor!

Connecting to a drive:

Bipolar (drive has A+, A-, B+, and B- terminals)

Bipolar Series (lower current required from drive, limited speed):

1 to A+

2 to 3

4 to A-

5 to B+

6 to 7

8 to B-

Bipolar Parallel (more load on drive, better speed):

1 and 3 to A+

2 and 4 to A-

5 and 7 to B+

6 and 8 to B-

Unipolar (drive has A1, A2, Act, B1, B2, Bct terminals):

1 to A1

2 and 3 to Act

4 to A2

5 to B1

6 and 7 to Bct

8 to B2

For a five wire unipolar, use the 6 wire connection, and hook Act and Bct together.

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Last edited April 29, 2007 5:31 am by Jmkasunich (diff)
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