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Can I make my power supply fan turn faster?
Steve Hough wrote:
Rene Lamontagne was thinking very hard :
WARNING !!!!!! IF you open up the PSU be warned that the large Caps
can store a very dangerous Voltage. If your not familiar with This
stuff, leave it alone and buy a new PSU.
Indeed. As the o/p has already managed to squirt the wrong oil into it.
I'm surprised so many others here advocated opening the thing up. And if
he waas familiar with this stuff, I doubt he would have uses WD40 in the
If the fan is soldered to the PCB, I would not
attempt to replace the fan.
If the fan uses a connector, you may be able to
unplug the connector. The most dangerous part,
is trying to use tools to torque the connector
to get it loose. If a tool slips off, it could
hit a high voltage item.
In any case, this is one reason the fan connector
is on the periphery of the PCB and not in the
middle of it. You don't have to get "up close
and personal" with the main cap, to change out
There is as much danger in making the main caps
"safe", as there is in working around the main
To see which caps are dangerous, there is a sample
schematic here. Modern PSUs don't use the same
architecture (they do double forward conversion),
but in terms of safety issues, this is a good
Capacitor C5 and C6 are larger devices (tin cans),
which are charged to 300VDC or higher. If you work
out 1/2*C*V^2 , the number of joules involved
is similar to that of a microwave oven cap.
*Do not* stick a screwdriver across the two
wire ends of a C5 or C6 cap, as the noise
is loud enough you could lose an eardrum.
1/2 * 0.000470 * 300 * 300 = 21 Joules
Resistor R2 and R3 are bleeder resistors. They're
in the circuit, to drain C5 and C6 after about
an 8 minute delay. That's a safety feature.
If we didn't need safety, R2 and R3 would not
even be in the circuit. They only have one
reason for being there. (I count waiting five
time constants as being long enough.)
But technicians working on a circuit like this,
assume R2 and R3 are defective and have gone
open circuit. And they further assume C5 and C6
are fully charged (it's a bit like defusing a bomb).
If a technician wanted to solder something on
the bottom of the PCB of the power supply, they
would use an *external* bleeder resistor to quietly
(and slowly) discharge C5 and C6. There is always
the danger of getting a shock, while making the
caps safe! (If you make a bleeder, you make yourself
some Plexiglas handles to position it, and
If I see that the fan connector is "off to the side"
and I can work on the low voltage fan connector
without getting near C5 and C6, I'll do that.
If the fan is soldered to the PCB, I would probably
decline to work on the project and just buy a new PSU.
I only got one decent shock in all my time
doing electronics. I got my "teaching" shock as a kid,
working with an ignition coil. One minute I was
at the workbench, the next minute I was getting
myself off the floor, and I apparently had
jumped backwards and hit the floor when the
shock got me. I'd laid something on top of some
wires, and didn't see a HV wire underneath something
else, and that's how my little experiment "got me" :-(
I've worked on high voltage since then, with
no other incidents to report. For example, I
have a flyback circuit with a tripler on the output,
for HV work, and that circuit has never managed
to get me. It would likely burn as much as shock.
But the reason I've not had a shock since, is
the first lesson was *the best* :-) You couldn't
ask for a better lesson. I presume I passed out
for a moment, but I'm not really sure. Because
I don't know exactly how I hit the floor.
Some of my other experiments as a kid, did more damage.
That one wasn't the worst. A good lesson is one
you learn without bleeding or a concussion.
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