Re: [CAD_CAM_EDM_DRO] Re: UPS to VFD hardware hack

turbulatordude wrote:

> >the output voltage needs to be varied proportional to the output
> frequency.
>
> This is the kicker. you must vary the voltage proportional to the
> frequency. you could get away with 10-20% off the nameplate, but
> your motor would overheat when fed the unexpected power.

Most smaller UPS's have an output transformer to step up the output
voltage. This transformer suffers the same problem as the motor, it
needs the applied voltage to be reduced (or PWM modulated) to
prevent saturation of the iron at reduced frequencies. The UPS would
either self-destruct, or at least blow fuses (and, most likely power
transistors, too) if the frequency was reduced.

Anyway, all smaller UPSs are single phase, and the starting switch
(and starting capacitors, if so equipped) will not work properly at
reduced speeds and frequencies. Only 3 phase motors work really
well for variable speed.

Jon