RE: [CAD_CAM_EDM_DRO] Re: Running Unipolar steppers with a Bi-polar driver?

Jeff,

Nice to see you on the CAD_CAM group.

I have to dissagree with you a little bit on this. You are correct that
the inducance is 4X and the resistance double only if you connect the
motor as bipolar series. If you instead connect it as half coil your
inductance and resistance is identical to a unipolar (you are running
through the same amount of coil) and if you connect it as parallel your
resistance is 1/2 and one of the electronic gurus (Help Mariss!!) will
have to quote on the inductance, but it is not 4X the half coil
(unipolar) rating.

So, depending how you connect it your running torque can vary. Just take
a look at the torque curves for parallel and series connetion that many
of the motor makes have and you will quickly see the difference.

Tim
[Denver, CO]
Sherline products at Deep Discounts www.KTMarketing.com/Sherline

> -----Original Message-----
>
> Hello Peter,
> When you run stepper motors in bipolar mode you will be driving
> twice the amount of copper (compared to unipolar). This turns into
> TWO times the resistance, and FOUR times the inductance the drive has
> to overcome, thus the time to fully energize the coils will DOUBLE.
> As you start getting faster and faster step rates, your drive doesn't
> have time to fully charge/discharge the current in the coils to the
> proper level. Thus at HIGHER step rates bipolar can end up having
> less torque than unipolar (given equivalent voltages for both
> drives).
> The good news is that the holding torque, or torque at slower step
> rates will be about 1.414 times MORE than a unipolar drive. This is
> where most of the power is really needed; when cutting metal at the
> slower, non-rapid feed rates.
> If you can find datasheets for your motor, they might show torque
> curves for both unipolar and bipolar. You can go from there when
> deciding on whether to choose a bipolar or unipolar drive.
>
> Jeff
> www.xylotex.com
> The XS-3525/8S-3 is a bipolar 3 Axis 2.5Amp 35Volt Stepper Driver
> board