Sola constant voltage transformer to clean up UPS output??

[CaptDon]

Have any of you tried one of those Sola ferroresonant constant voltage transformers to convert the crappy waveform of a UPS to a semi-sinewave? Did it work or is the harmonic distortion on the input to the Sola so bad that the output gets weird? I can say one thing about the C.V. transformers run from small R.V. type gasoline generators, Don't Do It!!! Our Onan generator on our mobile broadcast studio had so much frequency shift with changing loads that the voltage varied WILDLY!!! Like 80 to 170 kind of wild with just a 2hz frequency shift up or down. Also, when run lightly loaded they seem to really waste a lot of heat in the transformer core.

[james_s]

I haven't tried but I think you're going to experience similar problems. If you want a sine wave my suggestion is to buy a pure sine UPS, they exist and are often marketed as PFC compatible.

[bdunham7]

I think the problem is that the input impedance characteristics of those 'voltage stabilizers' are horrific with or without a load, so whatever is driving it needs to be extremely 'stout', so to speak.  A typical modified-sine UPS or inverter generator is not going to like them very much.

[TimFox]

I'm not familiar with their current line-up, but back in the day they had two different types:  "harmonic-neutralized" and something else.  Both would maintain the output voltage reasonably constant at a voltage that depends on frequency, and had to be purchased for either 50 or 60 Hz.  The harmonic-neutralized types put out a reasonable sine wave, and the others were better for driving a rectifier.
From their current catalog, the "CSV" series and "MCR" series are both specified for 3% THD.  https://solahevidutysales.com/pdf/powerconditioners/cvs.pdf   https://solahevidutysales.com/pdf/powerconditioners/mcr.pdf
Due to their frequency dependence, they are probably not a good choice for following a generator with an unstable frequency.

[TheMG]

The logical solution is to get a UPS with a pure sine wave output. Lots of them around can be purchased second hand for cheap.

A modified sine wave UPS may not like the ferroresonant transformer. Also they are big, heavy, and rather inefficient at low loads.

I'm sure there must be some niche applications where a ferro would be suitable, but generally these days a modern double-conversion UPS does a much better job of stabilizing voltage (and frequency!) at much better efficiency and smaller size than a ferro. Only advantage I can really see to a ferro is low EMI/RFI and robustness.