Re: [CAD_CAM_EDM_DRO] Inverters/phase converters

In a message dated 07/05/2000 7:15:26 PM Hawaiian Standard Time,
jmelson@... writes:

<< > One other idea would be to step up voltage to the device so current is

> lower through the rectifiers? I'm not sure if this would work. Many
> VFD's will accept 440 volts?

These units do not convert voltage. You run 240 V motors with a 240 V
input,
and a 240 V rated inverter. You run 440 V motors with a 440 V input,
and a
440 V inverter. In theory, you could run a 240 V motor from a 440 V
inverter
with 440 V input, and program the motor for 240 V at 60 Hz. But, you'd
need a 2 Hp inverter to run a 1 Hp motor, as the current doubles when
the
rated voltage drops to half. Just look at the rated current on the
nameplate
of a dual voltage motor. Also, the 240 V motor has 1/4th the inductance
of
a 440 V motor, so the PWM peak current will not come out right at all
for
a 440 V inverter running a 240 V motor, and you would likely get false
overcurrent trips. So, you really get no benefit, and will pay extra,
to be
back where you started from.

Jon >>


Jon,

Thanks for the clarification. Yes, I was thinking of running a 240 volt
motor on a 440 vfd. I figured though wattage remained the same, the current
through the rectifier would be smaller. Hence lower heating. I have mentioned
the AC Tech VFD's? I have one that is 120 volt input, 240 volt output. The
one in my hand is a 1/4 hp, they make them up to 1.5 hp. Very nice for
smaller home based machine users wanting "industrial" variable speed motors.
The whine can be annoying. And a tad on the pricey side.....

Peter
THRD, Inc.