> On Oct 12, 2024, at 4:54 PM, Jon Elson via cctalk <cctalk@classiccmp.org>
> wrote:
>
> On 10/12/24 14:30, Paul Koning via cctalk wrote:
>> Years ago I commented (on this list, probably) that a "VFC" would likely
>> make a good 400 Hz supply. VFC is "Variable frequency controller", a device
>> that takes mains input and turns it into three phase output of a frequency
>> of your choice. The upper frequency is typically fairly low; I don't think
>> mine reaches 400 Hz but then again it cost me less than $100 for a unit that
>> can drive a 3 hp motor. That one takes either single or three phase (220
>> volt) input; larger ones are normally specified as 3 phase only though
>> chances are they would in fact work if you fed them single phase power.
>
> VFDs use IGBTs to create variable width square waves of about 400 V. These
> can be turned into appropriate waveforms with a filter, but you sure don't
> want to feed these directly into any kind of computer power supply directly.
>
> Jon
Yes, I've heard that. But why? Power supplies of that era start with a
transformer, which acts as a low pass filter, and after the rectifier there's
another filter. Sure you can turn the PWM waveform into sines, but I can't see
that it matters much.
paul
