Get free access to our online edition!

From the Q&A

With TJ Byers

Ferroresonance Transformer


I have a SOLA constant voltage transformer that I would like to use on the input power to my computers. However, I'm a little chicken to try it because I've been told that they put out lousy wave shapes that could destroy computer power supplies. I really don't know that much about how these things work, so I am looking for some good advice.

via Internet


SOLA transformers work on the principle of ferroresonance. Basically, it provides a constant output voltage using a saturated core transformer. Unfortunately, this arrangement "flattens" the top of the sine wave so it more closely resembles a square wave; some models use a loosely-coupled third winding with a capacitor across it that reduces some of the higher-frequency harmonics to  smooth out the waveform.

Ferroresonant transformers are mostly used with resistive devices, like photoflood lamps, and aren't recommended for use with capacitor-input power supplies because of voltage spikes on the waveform. They also have to be heavily loaded (typically 50% or more of rated power) to work, which makes them run hot.