3-phase power

[Grant Taylor]

On 1/4/22 11:04 AM, Paul Koning via cctalk wrote:
> I've said that too, and I've been told that this is not a good idea 
> for power supplies.  Something about the waveforms involved in VFDs.

My limited understanding is that VFDs simulate / emulate various 
frequencies by turning the output on and off (at full input voltage) 
such that the (sliding) /average/ of the output looks like it's a at a 
lower voltage.  So when you're early in the typical sine wave (first 
45°) the output is on a small percent of the time and off a large 
percent of the time.  Near the upper portion of the peak (45°-135°) the 
output is on a large percent of the time and off a small percent of the 
time.  Repeat that method on through the sine wave.  So, you end up with 
very odd shaped signal.

Supposedly motors (or any inductive load) can smooth the pulsations to 
behave more like a true sine wave of the simulated / emulated frequency.

Non inductive loads don't smooth / average things nearly as well.  Hence 
why you probably want to not use a VFD to power computer equipment.

At least that's my understanding.

> The other option, typically somewhat more expensive but cheaper than 
> an 11/780, is a rotary converter.  Those are 3 phase motors, sometimes 
> modified a bit, driven from single phase power that construct the 
> missing phase somewhat like a dynamotor would.
Wouldn't that be construct the /two/ missing phases?  You input one 
phase between the two lines and get the other two phases between the two 
existing lines and the added line.

> Those things produce proper sine waves so they are good to use even 
> with things that are picky.

Yep.



-- 
Grant. . . .
unix || die