Re: UPS to VFD hardware hack

Doug, I think you are overlooking one major thing and a few minor
ones. Major: the UPS gives you single phase output, the VFD gives you
three phase output. A VFD actually performs very complex control that
takes into acount all kinds of motor parameters and back EMF
feedback. It also provides functions like overload protection,
reversing, etc. A brand new 2HP VFD can be had for about $249. Take a
look at

www.dealerselectric.com

They sell the Tian Electric VFD under the Teco-Westinghouse (FM100)
and Motortronics (CSD) labels. This is a good value V/Hz mode drive.
These drives have a TTL I/O header that can be used as RS232 or RS485
with the addition of the appropriate drivers. Windows programming
software and a RS232 cable goes for about $50.

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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