UPS systems for the 3b1

[Bill Mayhew]

I use a square wave UPS with a 7-8 mS transfer time on my 3b1.  It
works just fine.  The 3b1 power supply has at least 100 mS of
ride-through reserve, so switching time of the UPS is no big deal.
The 3b1 power pack directly rectifies the line voltage, then feeds the
rectified voltage into a switcher.  The moral of the story is that
the input waveform doens't matter much as long as the rms value
of the voltage is the same as what comes out of a wall socket. (I
suppose there are extreme cases such as 1000 volt, 1 mS pulses that
would not work as expected, but no UPS on earth is going to put out
such a waveform.)

With the monitor swtiched off, a 3b1 with a miniscribe 6085 drive
and 2 megabytes of memory draws about 60 watts as measured with a
real watt meter that reads V*I*cos(phase angle).  I didn't feel
like bothering to measure reactive power.  With the monitor
switched on the power consumption is 72 watts.  (with the hard disk
not seeking in both cases)

"Monitor switched on?", you ask.  I installed a power switch on my
monitor.  I don't like the idea of leaving the CRT running while I
am not at home.  I've seen too many terminals at work have nasty
failrues related to the CRT; in one case a Televideo 950 actually
had a fire start from a defective flyback transformer on the
monitor power supply board.

Do not attempt to install a switch on your monitor with your
computer plugged in or switched on.  Do not install a switch if you
do not have reasonable electronic credentials.


Bill
-- 

Bill Mayhew  Northeastern Ohio Universities College of Medicine
Rootstown, OH  44272-9995  USA    216-325-2511
wtm at uhura.neoucom.edu   ....!uunet!aablue!neoucom!wtm