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

Jeff,

Much better.

I would point out that you do not have to use the full current when running
in bipolar parallel or half coil (unipolar style) connection. Yes you do
lose low speed torque, but we normally have more than enough of that so
there is no problem. It makes a pretty good setup for many situations.

The reason to run in half coil arrangement with a bipolar drive is that you
get almost all the performance of a bipolar parallel and can use 6 wire
motors. It is also easier to wire with an 8 wire motor when you do not have
the schematic.

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

----- Original Message -----
> Hello Tim,
>
> True, I was thinking of bipolar series when I mention TWICE the
> resistance and FOUR times the inductance (when compared to a unipolar
> drive) (bipolar parallel inductance will be the SAME as unipolar
> inductance, while bipolar parallel resistance will be HALF that of
> unipolar resistance). Although the inductance is 1/4 in bipolar
> parallel as opposed to bipolar series, the INDUCTIVE TIME CONSTANT
> remains the same for both bipolar series & parallel, while unipolar
> is about half of that. Thus, you still suffer at higher speeds for
> both bipolar series & bipolar parallel with respect to unipolar,
> while you gain the 1.414 power advantage at lower speeds.
> Bipolar drives are usually more expensive than unipolar drives, so
> why anyone would use a bipolar drive and run the motor in unipolar
> mode(only use 1/2 the copper) is beyond me. Nevertheless, it could
> happen so I guess I should have taken that into consideration. Lesson
> learned.
> Finally, looking at a chart for bipolar parallel vs. bipolar
> series, you can see they start out with essentailly the same amount
> of torque (slow metal cutting speeds), while at higher speeds
> (rapids, engraving & perhaps wood router speeds), the power rating of
> bipolar series starts to taper off sooner. This becomes especially
> evident at lower voltages, thus a bipolar drive with a higher voltage
> capability can give better top end performance (while costing quite a
> bit more too!). Probably the biggest concern between running in
> bipolar series as opposed to bipolar parallel is that there seems to
> be few chipset that can handle the higher current required to run in
> bipolar parallel (often > 4 Amps). To get the higher current (like
> when trying to get the higher voltage), you need to go to discrete
> components. This really make the drive more complex, and the price
> of the drive shoots up again.
>
> Does all of this sound OK now?
>
> Jeff
> www.xylotex.com
>