[rescue] [off-topic] Vacuuming your servers is like cleaning them with a Van deGraff generator

Mark Benson md.benson at gmail.com
Thu Jul 28 01:30:48 CDT 2011

On 28 Jul 2011, at 00:51, Phil Stracchino wrote:

> On 07/27/11 19:43, Robert Darlington wrote:
>> This generally works great, just remember to not let the fans spin.  It's
>> quite easy to get them going 10x faster than they were meant to go using
>> compressed air.  That means you're generating a good 120 volts back into
>> 12 volt regulator on the mobo or other parts in the PSU.
> Didn't we just cover (and debunk) this a couple of weeks ago?

Yes, and like I said back then, there's a much plainer and simpler reason for
not spinning the fans with compressed air. On less well made ones (like you
find in a most consumer PCs, for example) it kills the bearings meaning they
suddenly get mad cow disease just after you clean them out.

The DC back-voltage thing would depend on how the fan is constructed. IIRC
brushless motors don't generate current when spun, but straight up DC brushed
motors do. You can't always tell if a fan is brushless from the connections
because the driver circuit is usually on a PCB inside the fan housing, but I
think moderns fans  tend to be brushless as it's cheaper to manufacture and
lasts longer because of the lack of contact parts. I could be way off the mark
though, my knowledge is abased off radio control car motors :)

Mark Benson

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