Subject: Re: serial port control
To: Wolfgang Rupprecht <>
From: Ken Hornstein <>
List: current-users
Date: 02/10/1998 15:27:38
>Its not clear to me yet that sine wave output wins.  Square wave
>should be more efficient since you don't have the big dead-time
>between, the two peaks.  If the load is your typical PC switching
>power supply then it would really prefer to have the full ~170v peak
>voltage applied all the time.  The down side of square waves is a
>touch more RFI noise.  As an aside, normal DC-DC converters are sqare
>wave internally, as are switching supplies.  It just doesn't pay to
>round the corners of the wave unless one is running a motor or
>transformer or something like it that will get very upset at the high
>dv/dt of the square waves.

Well, I was never very good at analog electronics, buuutttt..... I do
notice that when running on the battery of a square wave UPS (which
really should be called a "battery backup", since they aren't "true"
UPSes) the monitor went to hell (looked like it didn't have much
horizontal sync) and the disk drive made this _gawd_ awful noise.
Somehow those things never made me feel very good :-)  And since all of
the high end UPSes all advertise "full sine wave output", it's either a
massive marketing conspiracy or there are sound technical reasons why
it's a good idea :-)

Oh, one last note .... I chose my UPS size by adding up the total
wattage ratings on all of my equipment and I ended up with a UPS that
can power my computer for ninety minutes :-)  I plan on putting a few
more computers on it, but it's still _really_ overpowered ... you may
or may not consider this a feature, but if your budget is tight, you
can probably get by on a much smaller UPS than you think.