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.

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Why are hemorrhoids called "hemorrhoids" instead of "asteroids"?

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.

Jamie

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

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40,000 Americans are injured by toilets each year.

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?

On Mon, 16 May 2016 23:19:41 +0100, Wayne Chirnside wrote:

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?

Which should be less than the 12V coming from the PSU, right?

"Mr Macaw" wrote in message news
On Mon, 16 May 2016 23:19:41 +0100, Wayne Chirnside wrote:

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?

Which should be less than the 12V coming from the PSU, right?

Back emf can be 5 - 8x the applied voltage - its the whole basis of flyback
EHT in CRT TVs. When designing solid state ign coil drivers for cars; you
have to design for around 200V peak on the LT winding.

The fan has a BLDC motor, so any back emf is contained by the internal
circuitry - although PC servicing sites advise against blowing dust and
fluff out of fans with compressed air. The magnetic rotor spinning round the
coils will develop voltage, but I'd expect any damage to be confined to the
fan itself.