Ferroresonant transformers and 3278

[William Donzelli]

Some VFDs are not just plain PWM pulses, but a stepped sort of thing
that sort-of approximates a sinewave.

As I said, all this depends on what VFD you are using, and what you
might have to act as a filter, and what the load is - a case-by-case
thing.

--
Will

On Tue, Dec 22, 2015 at 12:12 PM, Jon Elson <elson at pico-systems.com> wrote:
> 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 garage.
>
> Jon