The fact that power supplies have to have protection from inrush currents (that's the proper name for what happens at start up) should tell you in itself that turning the pc on is not good for the pc. You only need one of these to be slightly off tolerance and some of that inrush could get through to more sensitive devices.Originally posted by ilw@1 August 2003 - 13:13
Light bulbs blow when they're switched on because the little coils inside them act as an inductor and sudden switching on causes the voltage across this inductor to spike which can destroy the very fine wire. (Hence my comment near the start about power supplies taking the brunt of switching on and off, but power supplies are built with smoothing circuits nad protections against that kinda thing)
And of course the inrush current effect is also true for the devices themselves (particularly electromechanical ones such as fans, disk drives etc). As has been said before, there is also the thermal shock effect (which, combined with inrush current, is actually what causes most lightbulbs to blow).
The inrush currents when light bulbs fail can often trip the circuit breakers, that's a lot of power even though it is only for a few milliseconds. Imagine what sort of damage that can do to your power supply. And if your power supply fails at that point (and I've seen it happen) that energy can be transfered to the rest of your system.
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