Ferroresonant transformers and 3278

Jon Elson elson at pico-systems.com
Tue Dec 22 11:12:30 CST 2015

On 12/22/2015 10:25 AM, William Donzelli wrote:
> Another thought - with scrap transformer prices in a crapper right
> now. you might also be able to pick up a really beefy isolation
> transformer for spare change, in order to clean up a VFD. Generally,
> normal industrial grade 50 Hz transformers will not care too much if
> you use them at 60 Hz.
An isolation transformer will NOT "clean up" a VFD's 
output.  The output of a VFD is NOT some dirty sine wave, it 
is a train of 400 V PWM pulses with perhaps a 15 KHz carrier 
frequency.  It could be filtered, but would take a filter 
built out of a bunch of HUGE inductors and capacitors.  It 
might actually be a decent solution for keeping 
museum-quality gear running in an unaltered state, but it 
isn't something you could whip up in a couple hours in your 


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