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I have one stepper motor.

There are six wires coming out of that.

How can I find out weather I have a bipolar or a unipolar stepper motor?

Note: Related, but not a duplicate: Unipolar and Bipolar Stepper motors

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You have a third type of motor: A "Universal" motor.

This is a motor can can be configured as either a unipolar or a bipolar motor.

General rules:

  • 4 Wires: Bipolar only
  • 5 Wires: Unipolar only
  • 6 Wires: Universal
  • 8 Wires: Universal

A unipolar only motor has the center of both windings connected together internally. This precludes the use of the motor in a bipolar system.

With a motor with six leads, if you connect the leads from the center of each winding together, you get a unipolar motor. If you leave the center connections unconnected, and drive each winding using only the connections to the winding ends, you are using it in bipolar mode.

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If your stepper has six wires, it can be used as a unipolar motor because you have 2*3 wires, where one of the three wires (each) is a center tap and the other two wires are one or another end of the same winding started at this center tap. Please see the appropriate section of the wikipedia article about steppers.

Bipolar motors have four wires; two for each winding. To reverse the poarity of one winding, you electronically switch it the other way round instead of switching on one end or the other of a center-tapped winding.

There are also motors with eight wires. These have four windings that can be connected in series like a center-tapped, bipolar motor or in parallel like a unipolar motor.

Here is a link to a well-written example of a datasheet. It details how you can configure a stepping motor in a biploar or unipolar way. You can figure out how pre-made unipolar or bipolar motors with six, five or four wires are really just cost- or space-cutting "wire-savers" compared to the flexible eight-wire types.

Hint: Use an ohm-meter to find out which three wires belong together. To see how the polarity is configured (What's the center tap? Which end is which?), connect an oscilloscope with at least two channels and turn the motor by hand.

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  • \$\begingroup\$ in my motor there are six wire and 2 of which are connected and finally there are five wire comes out of it. I have tested it with multimeter. when i test 1,2,3,4 alternatively for resistance it shows 2 times the resistance of any of the above(1,2,3,4) with 5th one(previously mentioned 2 wires) \$\endgroup\$ – vijay Jan 10 '12 at 12:35
  • \$\begingroup\$ Please check the data sheet I've provided a link to (p.3, top right). There's a schematic ("5-lead") that explains the connection of your particular motor (except for the wire colors, maybe). \$\endgroup\$ – zebonaut Jan 10 '12 at 13:14
  • \$\begingroup\$ Another 8-connection variant is a three-winding motor, with three hall-effect sensors and power and ground for them. I've seen that arrangement for floppy-drive-spinning motors. BTW, I wonder why steppers are usually two or four windings rather than three? Using three windings yields a pattern of six equal steps, rather than a pattern of four "strong" and four "weak" steps. \$\endgroup\$ – supercat Jan 10 '12 at 15:43
  • \$\begingroup\$ Unipolar motors have five wires. Motors with 6 or 8 wires are generally called "Universal" motors, as they can be used as either unipolar or bipolar. \$\endgroup\$ – Connor Wolf Jan 10 '12 at 20:58

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