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fan switch problems

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Jun 14, 2001
Athens - Greece
I read somewhere that switching fans on and off while the system is running (with homemade switches) could damage the HDD, mobo, cpu and all the parts of the pc. is that real or just a rumor?
Yeah, I think suddenly removing a device from a main power line or supply will cause fluctuations in the supply voltage and current. These fluctuations will be stabilised by your PSU but not fast enough to prevent some devices from hanging up, and given the delicate nature of most electronic components, damaging them with these voltage and current transients may be very possible. Any electronics/electrical engineer to confirm this?
I can relate to this. I can't boot my computer with all my case fans running. If I try I can hear my hard drive clicking on and off. My fans are on a switch with a rheostat. If there up more than half way my comp won't boot, I get a windows fatial exception error and have to reboot with the fans off. Once I'm booted up I can turn them on with out a problem. I watch the voltages on my motherboard monitor and the fans don't seem to make any difference in voltages. They voltages stay at the same values fans on or off. The only time I have problems is during boot up. Weird...although i'm not 100% positive this is what's causing the fatial errors but its what I suspect.
zoopa_man: Devices take more power to start up then they do to run. Sounds like you should be looking into a better psu.
The transients generated by suddenly adding or removing a load on the motherboard headers propagate throughout the motherboards 12V path, on their way back to the PSU. That path is connected to many components that can be sensitive to transients. Conversely, if you power your fans from an unused molex 4-pin plug out of the PSU, the transients propagate directly to the PSU. You can still have problems, especially if your PSU is operating on the edge of its capacity, but the chances are greatly reduced. My 170cfm blower draws 10 times more current than the most powerful axial fan you are likely to encounter in a PC case, yet I can plug and unplug it at will, without my system hiccupping.

hmm, thanks guys! I'll make some switches for my fans too. they're really loud nd i don't need them when i'm not gaming so i can simply turn them off when not needed. afterall, if i fry my system it's not that bad: I want t buy new pc anyway :)