[CentOS] [OT] ups advice

Thu Apr 14 19:29:26 UTC 2011
Lamar Owen <lowen at pari.edu>

On Thursday, April 14, 2011 02:51:02 PM John R Pierce wrote:
> switched PC/Server PSU's *so* don't give a bleep about sinusoidal power, 
> its not funny.   first thing they do is full wave rectify the power to 
> DC, then they run that DC through a high frequency (several 100Khz 
> usually) oscillator and into a toroidal transformer.      they would be 
> perfectly happy running off a full squarewave

Actually, a squarewave with the same RMS as a sine wave will full-wave rectify and filter to a lower DC voltage than the sinewave.  The supply may or may not be able to deal with that.  

To work the math, 120Vac RMS yields a peak voltage for a sinewave of about 170V (Vpeak=Vrms*square-root-of-two); full-wave rectified and filtered that gives 170V DC (with some ripple, depending upon the size of the filter capacitor relative to the current drawn); a squarewave at 120Vac RMS yields a peak voltage of 120V, and a filtered DC of 120V, equal to the filtered DC for an input RMS AC voltage of 84Vac RMS (for a sinewave, Vrms=Vpeak/square-root-of-two); if your power supply can deal with that.....

Also, the odd-order harmonics may create their own havoc in the filtering.  So, no, there's more to it than meets the eye.

I are a EE; degree and all..... :-)

But if you don't believe me, please look at:
and come back later....