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Wayne Chirnside[_6_] Wayne Chirnside[_6_] is offline
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Default Flimsy power supply won't drive a little fan!

On Wed, 17 Feb 2016 15:54:29 +0000, Mr Macaw wrote:

On Tue, 16 Feb 2016 23:50:38 -0000, M Philbrook
wrote:

In article , says...

I have a pile of power supplies which used to power CCTV cameras.
They're rated at 12V 1A. They're very light and give out precisely
12V with no load, so they must be regulated switched mode. So why is
it when I try to power a 0.15A 12V fan (a 120mm Corsair computer fan),
they fail very quickly? The first one started whining and gave out
only 0.5 volts after only half an hour, and the second one went pop
after half an hour. I've had two of the others powering door

entry RFID coils and the door solenoids and they've been happy for a
few years.

Most likely bad caps , that is most common failure mode for them.


But for two of them? When another two (of the same age from the came
camera set) have worked for a couple of years powering door locks?

I've opened them up, this is what they look like. I can see the power
transistor in the top one (the one that whistled and produced bugger all
voltage) has been warm enough to discolour and crack the yellow wax
stuff (ringed in green), but the caps look fine. In the one that went
pop, a fuse has exploded (ringed in red).
https://www.dropbox.com/s/q1sc56tx0vtmzuv/PSUs.jpg?dl=0


Back EMF from the fan?