[rescue] Rescued Sun servers, now what?!

der Mouse mouse at Rodents-Montreal.ORG
Fri Jun 17 10:29:21 CDT 2011

>> I tend to use compressed air from a regular air compressor.  The
>> trick with compressed air is to not let the fans spin.   They're
>> generators.  Spin em 10x faster than they normally go and they dump
>> 120 volts back into your circuit that normally supplies 12!

Not really.

First, many fans, particularly on peecees, have electronics between the
motor and the upstream power feed, circuitry that doesn't pass power
the wrong way well (or sometimes at all).

Second, they are not particularly good generators; they are optimized
for the other direction.  Even if you do spin it 11x normal speed,
which is difficult for most fans...even if it would generate 120VDC
open-circuit (why not 132V, btw?) when so spun...even if those, each of
which I find doubtful, it's not going to have much power behind it; put
a load on it and that 120V falls drastically.  I once amused myself by
taking two fans wired in parallel but disconnected from everything else
and using a vacuum to spin one.  I think I got the first fan up to
somewhat over normal speed, perhaps 2x normal, and even at that
extreme, the other one barely spun - it was not getting anything like
full voltage, never mind overvoltage.  Put additional load on it, like
the rest of the computer's 12V load, and I'd be surprised if it makes
it up to 2V.

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