Ferroresonant transformers and 3278

Jon Elson elson at pico-systems.com
Mon Dec 21 21:12:56 CST 2015

On 12/21/2015 09:03 PM, William Donzelli wrote:
> If you can get a rotary one, those are really nice - just wasteful and
> loud. With proper maintenance they last forever, can take a beating,
> and do not give waveshape issues that cheap solid state units can
> have. And, maybe most importantly, you can make one yourself.
> But considering the mix of 50 and 60 Hz stuff you likely have by now
> (that is what you get for moving!), spending some decent money on a
> real VFD might be worth it. I might think a cheap VFD may give
> ferroresonant iron fits with all those extra harmonics.
You can't run electronics with VFDs designed to run motors, 
only. They put out PWM chopped square waves at 300+ Volts.  
A motor's winding inductance smooths that out to a proper 
current waveform, and it only causes a little extra eddy 
current losses.  But, typical transformers will have real 
fits with that kind of waveform.

There are "frequency changers" made by Elgar and others that 
will do the job right, but they will cost a REAL bundle of 
cash!  (Also known as frequency converters.)

It may be possible to retune the resonant circuit of the 
constant voltage transformer by adding capacitance in 
parallel to the existing capacitor.


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