Re: 8-wire stepper: series is 1/2 the amps.Strange but True

Hi Dave,

> so, the question how does one determine where the torque starts to
> drop off when on is not using a single coil (on an 8 wire) but is
> using less than nameplate on a series wired motor ?
>
> Dave

I think torque will start to drop off when there isn't enough time
to charge the coil to required amperage before the next step pulse
comes in.

A microstepping drive, when set to full step mode, will generally
power each coil at about 71% of rated power. For full stepping you
would get the following (4 steps shown):
Ph.A Ph.B
+71% +71%
+71% -71%
-71% -71%
-71% +71%
and so on. As you can see, at each step, one of the coils is
reversing it's polarity. You can figure out how long it will take
the coil to go from + to - (or - to +).

I think the formula is going to be something like:
1 / (((Coil Amp *.71) / (Supply Voltage / Inductance in H))) * 2)

So a 4 amp motor with 4mH inductance driven with 40V would be:
1/(((4 amp motor *.71) / (40V/.004H)) * 2)
1/((2.84/10000)*2)
1/(.000284 * 2)
1/.000568
1760 steps per second
before it starts loosing torque.

I'm sure one of the other members out there can (and hope they will)
scrutinize this and let us know if this turns out to be to case,
close, or way off.

Jeff
http://www.xylotex.com