Text 285, 61 rader
Skriven 2005-03-23 08:46:00 av Greg Mayman
     Kommentar till en text av Roy J. Tellason
Ärende: FAN OF TRUE MULTITASKING
================================
 -=> Roy J. Tellason said to Greg Mayman
 -=> about "FAN OF TRUE MULTITASKING" on 03-09-05  20:06.....

 RJT> Now _that_ would be handy,  as I'm really not looking forward to the
 RJT> spring thunderstorms we normally get around here...

 RJT> I'm in fact thinking about acquiring a UPS to help in dealing with
 RJT> them. 

About 20 years ago I saw a commercial installation of a UPS that
cut out every time the mains power went down.

The problem seemed to be that the UPS was rated at 1kw with a
power factor of 80% or better.

OTOH the computer system it was powering was drawing less than
800 watts as measured, but EVERY part of it was powered with
conventional transformer + rectifier + capacitor input filter.

The peak current would have been several times the average or
RMS values and was almost certainly the cause of the UPS cutting
out.

But when I thought about the whole thing, I wondered about the
wisdom of supplying (in this case) 240v 50Hz sinusoidal AC to the
power supplies, when what was needed was DC at various voltages
for the components of the system.

Present day computers (apart from laptops) have all their
internals (and some externals) powered by a chopper power supply
that is fed with about 400v DC from a rectifier system directly
on the mains input.

Rather than have the UPS feed it from an inverter to deliver AC
to the computer, it would be much more efficient to connect a
backup battery directly to the input of the chopper in the power
supply.

Yeah, I agree a 400 volt battery is not something nice to play
with. But a modified form of the power supply could be powered
from say a 12 volt automobile battery.

The battery could be float charged from the mains, with a high
efficiency chopper supply.

This would make the computer virtually 100% proof against mains
power failures, and also buffer it against a whole host of other
nasties, like overvoltage spikes on the mains.

And the whole system would be much simpler.

   ,-./\
  /     \ From Greg Mayman, in beautiful Adelaide, South Australia
  \_,-*_/    "Queen City of The South"    34:55 S  138:36 E
       v

... We are all mortal until the first kiss and the second glass of wine.
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