"DoN. Nichols" writes:


But the VFDs normally use PWM to simulate the output sine wave,
not a true sine wave (which you get out of the better UPS, since some
computer power supplies are allergic to the voltage spikes from a PWM
emulation of a sine wave.)

The ferro-resonant tank circuit was what gave you sine wave. Most
give a rotten waveform but they knew a thing or two about building
them.

Such came with a big price tag, however. Those custom-wound magnetics
were big heavy, noisy & expensive 30 years ago; today you could buy a
wall-street bank with 2 of them.

Years ago, I worked at a company that made big 3 phase UPS's, as from
the 10KW to 10MW size.

Hmm ... Best Power Systems, by any chance? I really *like* their USPs,
and have three of them running at the moment -- all Ferrups models.

Long since gone, I suspect -- Lorain Products, later p/o Reliance
Electric, LorTec and then who knows. [I see "LTI Power Systems"] They made
"Perpetuac" units as well as lesser ones.

Yep -- "Sola constant voltage transformer". I've also got a DC power
supply in which the only regulation is that it was built around a Sola
style transformer. Probably a bit more efficient than normal linear
regulators, but less so than a switching regulator.

VERY inefficient at anything but 100% load. A FR draws 30% of FL at 0%
out; they are great heaters. But they eat all kinds of line crap and
never blink. They will coast past a few missed cycles with no problem.


Over 10-30 minutes, the motor would eventually come up to ~850 RPM, and the
current would drop to something normal. The module had passed..

Wow! *That* is impressive.

Damn right.
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