Carl Lowenstein wrote:
[snip]
Computer power supplies draw current in short high-amplitude pulses at the
peaks of the AC input. The RMS value of the current, and thus the heating
effect on a circuit breaker, is significantly higher than would be
calculated from the DC power consumption of the computer. The magnitude of
the effect can by calculated by a simple exercise in integral calculus,
which I have done in the past, but not recently.
For some education on this subject, look at
< http://www.harmonicslimited.com/docs/tech/what_r.html >.
And associated follow-on pages.
While that used to be true, power supplies now use power factor
correction to specifically avoid that problem. In Europe you cannot sell
a power supply without power factor correction, while in the US the
really cheap ones might not have it but the more reputable brands do. My
PC Power and Cooling supply corrects out to 98% and the newer ones to 99%.
For those that don't know, power factor is a measure of how close the
load is to an ideal resistive load, which means the current exactly
follows the applied voltage, as opposed to a reactive load where the
current may lead (capacitive) or lag (inductive).
Gus
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