Re: UPS to VFD hardware hack

I forgot to mention that there are a bunch of other reasons that you
don't want to waste time with this idea even if you had one of the
very expensive 3 phase UPS models. A few would be that the output
voltage needs to be varied proportional to the output frequency. Most
UPS are not true online so they don't synthesize the output when
there is line power. The ouput drivers in the UPS may not be suitable
for use at other frequencies. It's very unlikey that you would find a
60Hz reference. Most UPS have a microcontroller which may be used to
generate the ouput waveform so changing a clock reference won't
really do the trick. And there are many more.

Best Regards,

~petev

--- In CAD_CAM_EDM_DRO@y..., Doug Fortune <pentam@c...> wrote:
>
> 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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