Open up a power supply
FreeSpeech
I have an AOpen HX08 full-tower case with an AOpen 300w power
supply.
I am thinking of replacing the aging fan in it with a slower and
lquieter fan although it is the same size.
I've read somewhere that it's plain dangerous to open a power supply
and change the fan in it. It seems that the power supply uses big
capacitors that absorb current and stay this way for several hours
after the power cable has been unplugged. Is that true ? It seems it's
a big electrical hazard... !*#&?#! ;-)
If I remove the power supply from the box and leave it on the table
for several hours, will the capacitors end up empty so I can replace
the fan safely ?
Thanks,
Dave
bobb
wrote:
Nope, you are talking about a TV picture tube. In a switching power
supply, the capacitors are low voltage DC. Go for it. Just be sure
you are using the same type of fan (AC or DC and correct voltage) and
facing it the right way when you mount it.
-bobb
Lucas Tam
Just leave the box for a couple of minutes before working on it. I haven't
recevied a shock yet... hmmm...
FreeSpeech <bla...@blabla.com> wrote in
news:387n9ug6dubnd75k0...@4ax.com:
Eric
> If I remove the power supply from the box and leave it on the table
> for several hours, will the capacitors end up empty so I can replace
> the fan safely ?
To be safe, leave it on that table overnight. Some supply's 300v buss
discharges faster than others.
--
Better than hearing "Lady Day", or checking in at Monterey...
[Remove bodies from address for email.]
Lane Lewis
of fire and or electrocution. That's why its sealed with a warning and
that's why only those with the proper training should work on such devices.
There's also a criminal and financial responsibility involved.
So even if it doesn't seem like much the consequences can be tremendous.
Lane
And Satan said to God, "But where will YOU get a lawyer?
"FreeSpeech" <bla...@blabla.com> wrote in message
news:387n9ug6dubnd75k0...@4ax.com...
Pokee Joe
>
>Nope, you are talking about a TV picture tube. In a switching power
>supply, the capacitors are low voltage DC. Go for it. Just be sure
>you are using the same type of fan (AC or DC and correct voltage) and
>facing it the right way when you mount it.
>
That's a pretty sick joke, bobb. Are you trying to get him
electrocuted?
PC Power Supplies have a direct coupled input, which means they do not
have an input transformer. Instead, the 120/240VAC is connected
directly to a diode, in series with a capacitor. The capacitor charges
to 1.41 times the RMS input voltage during operation, so you can
expect to find 170VDC or 340VDC in the power supply.
regards,
Joe
Zoogle
> So even if it doesn't seem like much the consequences can be tremendous.
So now they're trying to stop us from risking our lives to mod eh? What
next, maybe they'll make it illegal to build computers?? (whoops! That's on
the verge of being passed for u americans... :)
do_not_spam_me
> >I've read somewhere that it's plain dangerous to open a power supply
> >and change the fan in it. It seems that the power supply uses big
> >capacitors that absorb current and stay this way for several hours
> >after the power cable has been unplugged.
>
> Nope, you are talking about a TV picture tube. In a switching power
> supply, the capacitors are low voltage DC. Go for it.
Some of the capacitors are low voltage, but there's a pair on the
primary side that take rectified 120VAC or 220VAC and convert it to
370VDC. Those capacitors usually drain off completely in one second
after turn-off, but if something goes wrong they can retain high
voltage for hours. So anybody who doesn't know exactly what's going
on inside a power supply should first leave the supply unplugged for
several hours.
Ray
>
>To be safe, leave it on that table overnight. Some supply's 300v buss
>discharges faster than others.
What use would a modern PC switching supply have for storing 300v in a cap?
Bumping the voltage up that high just to bring it down later sounds horribly
ineffecient and bulky.
--
Ray
Pokee Joe
voltage on the AC line.
120VAC:A sine wave cycling between +170V and -170V or 340Vp-p
240VAC:A sine wave cycling between +340V and -340V or 680Vp-p
regards,
Joe
Ray
>The power supply doesn't "bump up" the voltage. That is the incoming
>voltage on the AC line.
>
>120VAC:A sine wave cycling between +170V and -170V or 340Vp-p
>
>240VAC:A sine wave cycling between +340V and -340V or 680Vp-p
Thanks, I'd forgotten about those strange places that use 240VAC :)
--
Ray
Eric
> Nope, you are talking about a TV picture tube. In a switching power
> supply, the capacitors are low voltage DC.
If you consider 300+ VDC low voltage. I don't.
Eric
> What use would a modern PC switching supply have for storing 300v in a cap?
> Bumping the voltage up that high just to bring it down later sounds horribly
> ineffecient and bulky.
Not at all. The input voltage is simply rectified and the caps charged
to the peak voltage of the AC input. That's 230 x 1.414 = 325 vdc. There
are two input caps. In 230 vac operation, they are connected in parallel.
For 115 operation, they are connected in series (effectively doubling the
115 x 1.414 voltage to the same 325 vdc.) Why? No input magnetics! The
switching transistor now operates at high voltage, low current. The
output magnetics have the correct turns ratio to provide the correct
output voltage.
gerrcoin
cable in, but switched off at the wall outlet, any residual power would be
grounded. Of course we use 3 Pin power outlets in the UK, on which one pin
is dedicated to grounding the metal case.
Unfortunately, I am used to leaving the outlet switched on when doing fast
changes within the case (as the highest voltage on the motherboard is only
12 V). As you might imagine, this is not a bright thing to do when you're
working on the PSU. My thumbnail accidentally touched the live contact, and
I thank my lucky socks for rubber soled shoes, otherwise I would not be
writing this today.
Don't take a chance. Unplug or switch off the power outlet, and invest in
and mains tester to check for high residual charge.
Gerr
"FreeSpeech" <bla...@blabla.com> wrote in message
news:387n9ug6dubnd75k0...@4ax.com...
Doug
It might give you a little kick but I don't think there is much more than
that to worry about. As long as it is unplugged I don't think he will fry.
You could always manually disgharge the caps that have the high V labels
with some sort of shunt. Ya I know you are not suppose to do that
either....... live a little have some fun. WHOOPS I SMELL SOMTHING BURNING
"Zoogle" <a...@me.com> wrote in message
news:33Um8.30046$Ff3.2...@news20.bellglobal.com...
Pokee Joe
had to sit through in my career as an electrician and electronics
repair technician...
There is fairly large nerve in the left arm, that passes behind the
heart, on it's way to the spinal cord. An electrical shock from as low
as 35V with as little current as 15mA, passing through this nerve can
destabilize the nerve center in the heart, that generates the timing
signals that coordinate the heart muscles. Once that coordinating
rythm is disturbed, you are in danger of the heart going into
fibrillation, which can be fatal. Anyone who sustains an electrical
shock to the left arm, should go to the hospital for an
electrocardiogram, which will show if there is any disturbance to the
rhythm. If there is, they will remain under medical observation until
the heart rhythm settles back down or defibrillation becomes
necessary. Usually, the heart rhythm will settle back down by itself,
within 24 hours.
regards,
Joe
On Sat, 23 Mar 2002 13:29:06 GMT, "Doug" <imaf...@mediaone.net>
wrote:
James West
--
.
"bobb" <nO...@NoWhere.com> wrote in message
news:3c9da7db....@news.mindspring.com...
Eric
> There is fairly large nerve in the left arm, that passes behind the
> heart, on it's way to the spinal cord. An electrical shock from as low
> as 35V with as little current as 15mA,
[...snip]
The amount of voltage present is somewhat misleading. It all depends
on what body parts come in contact with the voltage, and the amount
of electrical resistance presented.
To get your above 15mA from a 35v source would indicate a body resistance
of only 2333 ohms. Highly unlikely. Body electrical resistance runs
several hundred thousand ohms, but it does vary.
In addition, to get current to damage the heart a current path through
the heart is needed - i.e. from one arm to the other. This is the reason
those working on very high voltage usually keep one hand behind their back.
A 1KV voltage source may cause a nasty burn if just one hand comes in
contact (assuming well insulated shoes), but no lethal damage will occur.
A 300vdc buss may send quite a jolt, but it will probably only be lethal
if a) contacted across both arms, b) contacted by someone with very low
body electrical resistance, and/or c) contacted by someone with an
already weakened heart.
Lane Lewis
fire or electrocution. It's still a free country over here at least until
you try to be your own electrician (5yrs in the pen) but the main thing is
to take responsibility. If you damage you power supply and it burns down an
apartment complex, their going to come looking for you to replace it.
Lane
If it was easy, the hardware people would take care of it.
"Zoogle" <a...@me.com> wrote in message
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