Will wiring a unipolar stepper to a bipolar stepper driver decrease the holding torque?

Question

I have read that you can wire a unipolar stepper to a bipolar driver, which I have, by ignoring the two extra wires. One concern I have is whether connecting a unipolar stepper to a bipolar driver will cause it to lose torque (holding or operating)?

Will it be the same? Increase?

I've read that bipolars are more bang for your buck energy-wise, and since you can "transform" a unipolar stepper to a bipolar good enough that the driver will still work right, I would think that it might run more efficiently. Is this true?

Answer 1

From wikipedia http://en.wikipedia.org/wiki/Stepper_motor

Because windings are better utilized, they are more powerful than a unipolar motor of the
same weight. This is due to the physical space occupied by the windings. A unipolar motor has twice the amount of wire in the same space, but only half used at any point in time, hence is 50% efficient (or approximately 70% of the torque output available). Though a bipolar stepper motor is more complicated to drive, the abundance of driver chips means this is much less difficult to achieve.

If you read specifications for a stepper motor that can be wired as unipolar/bipolar, you will confirm this.

But if you have a 5 wire unipolar, the central one is common to the center tap of both coils. You need to remove this connection to use it as bipolar. If you have a 6 wire, yes it is meant for that, just ignore the two other wires (some motors have connectors so you can disconnect the wires), and run it as bipolar.

^{From http://www.esuli.it/2011/10/11/converting-an-unipolar-stepper-to-bipolar/}