UPS to VFD hardware hack

A UPS (uninterruptable power supply) works by:
- taking input of 60 HZ AC
- converting to DC, possibly storing in battery
- converting DC back to 60 HZ AC (called inverting or inversion)

Somewhere in the inverter circuitry, there must be a
60 Hz reference oscillator (and of course, a 50 Hz
reference oscillator would be installed in England),
required in order to synthesize the output waveform.

As it happens, the output rpm of AC motors are locked to this
frequency, but if the frequency changes (say 15 Hz to 120 Hz)
then the basic speed of the AC motor can go from 25% to 200%
of its normal rpm.

I had the idea that this fixed oscillator be hacked out,
and a variable frequency source be installed in its place,
thereby possibly achieving an inexpensive AC VFD
(variable output frequency motor driver).

This pertains to CCED in that this variable frequency
is controlled somehow by the computer, leading to
variable speed spindle control (of your lathe or mill).

Has anyone got any intuition as to whether this might
be possible? Inexpensive UPS's are available up to
1500 VA (approx 2 HP).

Doug Fortune
http://www.cncKITS.com





















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