Ferroresonant transformers and 3278

William Donzelli wdonzelli at gmail.com
Mon Dec 21 21:37:09 CST 2015

I have heard that some guys have put a motor in the circuit just to
deal with the harmonics as a filter to shore the sine wave up. An
interesting idea, worth a try, but I bet it works on a case-by-case


On Mon, Dec 21, 2015 at 10:12 PM, Jon Elson <elson at pico-systems.com> wrote:
> 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.
> Jon

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