Re: [CAD_CAM_EDM_DRO] stepper torque.....please help

Kayla Sanders wrote:

> i wanted to ask you all something .....i have 3- 305 oz-in motors
> @4.5A per phase and 2Vdc ,using a 28 Vdc/12 A power supply,direct
> drive config.. i was thinking about going with an "FET-3" 3 axis
> unipolar controller rated up to 15A per phase with proper cooling
> from stepperworld.com (only 135$ compared to gecko's at 114$ each)
> (are the FET-3's any good?).....being that the rated torque of the
> motors are for bipolar parallel, what would the approximate torque
> drop be when hooking them up to a unipolar controller in parallel??
> and is it going to hurt these motors using this power supply at this
> amperage? the capacitors that i choose will reduce the current to
> the motors?? or the voltage?? or both???

First, if these are 4-wire motors, they can't be used with a unipolar driver.
You need 6- or 8-wire motors to make the right connections.

You mention a unipolar driver in parallel. That doesn't make sense.
With 8-wire motors, you can select either parallel or series connection
for a bipolar drive, but you can only connect the motor one way for
unipolar.

The holding torque will be about the same, assuming the motors can
be used on a unipolar drive. The real difference is when the motors
are moving. Many unipolar drives don't drain the current from the
winding that has just shut off very quickly, so the rise of the current in the
opposing winding rises slowly. R/L drivers are the worst in this regard,
and you should avoid these like the plague. Anyway, in general,
a bipolar driver will perform better than a unipolar. And, a chopping-type
drive will always perform better than an R/L driver.

An overrated power supply will NEVER hurt the motor, as the driver is
responsible for limiting the current. The capacitors in the DC power
supply STABILIZE the supply voltage. They do not alter the current
or voltage.

Jon