Re: [CAD_CAM_EDM_DRO] Re: Gecko and Anaheim

john@... wrote:

> Sorry to butt in on this thread but Mariss's original reply is copied
> below.
> Mariss states
> >" To get the maximum power from a 7A, 80V drive, pick a 7 Amp, 4
> >volt motor. "
>
> Surely a 4V motor running on 80v supply will burn out.
> Am I missing something here ?

Yes. The stepper drive (either resistive or chopping) limits current to
a
preset value, usually the motor's rated current. With a resistive
drive, a
resistor is placed in series between the power supply and the motor
(simplifying things a bit, here). With a chopper drive, the connection
between the power supply and the motor is broken and reconnected
at a rate of several thousand times a second, once winding current
reaches
the preset value. The duty cycle is controlled to hold this rated
current
in the motor windings. But, the advantage is that the windings DO see
the full power supply voltage during the instant it takes for the
current
to ramp up (due to winding inductance). The 80 V allows the current to
ramp up very quickly, permitting the motor to step much faster than
with a lower voltage. The fluctuating current and voltages do cause
some
additional heating in the motor. But, the winding insulation is
designed to
handle much higher voltage than the rated voltage for the winding, which

takes only pure resistance into account.

Jon