4. Eight-lead unipolar/bipolar stepper motor connections

An eight-lead stepper motor, is similar to a six-lead motor but gives you access to all of the half-coil leads (in a six-lead motor, lead A′ is internally connected to C′ and lead B′ is internally connected to D′). This gives you an additional connection option.

Half-coil

As with a six-lead motor, you can connect half of each coil to the driver; for example, you could connect stepper leads A and A′ to one pair of driver outputs and stepper leads B and B′ to the other pair of driver outputs, leaving C, C′, D, and D′ disconnected.

Full-coil series

As with a six-lead motor, you can connect both full coils to the driver with the half-coils in series by connecting stepper lead A′ to C′ and stepper lead B′ to D′. Then, stepper leads A, C, B, and D should be connected to the stepper motor driver as with the six-lead motor, and you should similarly limit the coil current as described earlier in Section 3.

Full-coil parallel

You can connect both full coils to the driver with the half-coils in parallel by connecting stepper leads A and C′ to board output A1, stepper leads A′ and C to board output B1, stepper leads B and D′ to board output A2, and stepper leads B′ and D to board output 2B. Like full-coil series wiring, this also changes the characteristics of the motor, but in a different way: it will have half the rated resistance, but its inductance does not change from the rated value. Therefore, this wiring method does not limit the maximum step rate of the motor as much as full-coil series wiring, and compared to half-coil wiring, this method offers the advantage of lower power dissipation and heat at the same current due to the lower coil resistances.

Since the power dissipation at the rated current is less than what the motor was designed for with this wiring method, you might be able to get more performance out of the motor by increasing the current beyond the rated value. (Halving the resistance means the current can be multiplied by ``sqrt(2)``, or about 140%, while keeping the power the same.) However, magnetic saturation of the motor might limit the improvement you can get from increasing the current like this.