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From: grege@gold.GVG.TEK.COM (Gregory Ebert)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Leave the PC on vs. Power it off daily?
Message-ID: <1518@gold.GVG.TEK.COM>
Date: 28 Sep 90 16:10:55 GMT
References: <8axQEga00VY642bGAb@andrew.cmu.edu> <1990Sep27.190011.12366@sj.ate.slb.com>
Organization: Grass Valley Group, Grass Valley, CA
Lines: 28


 poffen@sj.ate.slb.com (Russell Poffenberger) writes:
>
>This is simply not correct. First of all, the "switching" section of the supply
>is powered by DC, after the AC line as been rectified and filtered. The
>filtering (using large capacitors) masks any load changes caused by the
>switching action of the supply.

There IS a problem, though, with the rectifier section: It makes NASTY current
spikes when the capacitor charges (briefly).

There was a large fire in downtown LA which was attributed to the switchmode
power supplies in PC's (Union Bank building, not ARCO tower). The power
distribution system assumed balanced 3-phase loads, but many of the PC's,
which have a non-unity power factor, caused a large imbalance in the power
system. This results in a large current in the neutral line, which would
normally be zero, and an electrical fire started. The degree of imbalance
peaked at night because PC's were left on, while lights and air-conditioning
equipment were cut back.


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