Capacitors in PSU are dangerous?

Actually, I did misread that. But considering the whole thread so far has
been about the PSU's (not the other wires in a PC case), and because the PSU
is inside the case, I'm still right. So there.

Clint

"Kevin Lawton" wrote in message
...
Parish wrote:
| Kevin Lawton wrote:
|
|| Clint wrote:
||| Hmmm. So it's the power cord plugged into the wall that converts
||| the 120V wall supply down to 3, 5, and 12V? I wonder why they
||| bother
||| with that great big box then?
||
|| Eh ? What ? Where did you get THAT from ?
|
| I think he misread "The wires inside the PC case only carry 3.3v, 5v
| and 12v..." in your previous message as "...PSU case..."

Yes, I think he probably did.
Kevin.

'still right' ? ? ?
Technically correct in that there are high voltages inside a PSU - yes.
But as far as taking the **** when you misunderstood me and then not
printing a retraction - I think that pistols at dawn would be appropriate,
or maybe you'd prefer swords ? .
BTW: If you try reading the entire thread then you'll see that it was not I
who introduced the question of what voltages could be accessed inside the PC
case without opening up the PSU. I was replying to someone's question.
Someone who, as I recall, stated that they were a carpenter and would
replace a faulty PSU rather than open it up.
Sire, I feel that you have been paying insufficient attention to be able to
keep up.
Kevin.

Clint wrote:
| Actually, I did misread that. But considering the whole thread so
| far has been about the PSU's (not the other wires in a PC case), and
| because the PSU is inside the case, I'm still right. So there.
|
| Clint
|
| "Kevin Lawton" wrote in message
| ...
|| Parish wrote:
||| Kevin Lawton wrote:
|||
|||| Clint wrote:
||||| Hmmm. So it's the power cord plugged into the wall that converts
||||| the 120V wall supply down to 3, 5, and 12V? I wonder why they
||||| bother
||||| with that great big box then?
||||
|||| Eh ? What ? Where did you get THAT from ?
|||
||| I think he misread "The wires inside the PC case only carry 3.3v, 5v
||| and 12v..." in your previous message as "...PSU case..."
||
|| Yes, I think he probably did.
|| Kevin.

Kevin Lawton wrote:
VWWall wrote:
snip
Typical values are 220,000 ohms across 470 mfd capacitor charged to
about 170 V. This is about 1/8 watt lost in the bleeder resistor.
Incidently this is a time constant, (RC), of about 100 seconds. The
voltage will drop to 17 V in 2RC or 3 minutes 20 seconds, assuming
no other leakage paths.

You'd be working pretty fast to get the PC opened up, detatch all the
power cables, remove the PSU, get it on the workbench and open it up
in that time !
Pretty safe unless the bleeder resistors have failed.

Yep, agreed. I was just wonderinbg how much power these bleeder resistors
were wasting while the PSU was running. Not a lot obviously. However, it all
adds up. 1/8th of a watt per large cap, I have five PCs running most of the
day (and night). That's gotta be a big mac every couple of weeks.
--
~misfit~

Christiaan van Bladel wrote:
Regal schreef:

I read on some website that the capacitors in a PC's PSU can hold a
charge for long after they have been switched off and that the
charge could be fatal.

Is this really so? Surely that is exaggerating?

Yes, capacitors can hold a charge for a long time. But in most casses
this is a result of a defect in the PSU, in most casses the
bleederresistor, like mensioned before. When you want to open a
computer PSU, one that works correct, do the following

1 Turn off the computer
2 Disconnect te powerplug
3 Turn on the computer with the powerplug disconnected

I always do that before moving the 'clear CMOS' jumper, and before opening
up a PSU, usually for fan replacement.
--
~misfit~

Stap 3 will unload any loaded cap. The same goes with other apparatus
that works normaly. If an apparatus is defective than the cap can stil
be charged. I've seen, and experionced, cases where the cap was loaded
for over a month and still zapped the hell out of me. If it is fatal,
i dont know but it hurts like hell, it can burn your fingers, and
isn't very pleasant.

If you ever feel the urge to open an electrical apparatus, think about
what your doing, think again, and pray to your god that the
bleederresistor isn't defective.

Succes
Chris

~misfit~ wrote:
| Kevin Lawton wrote:
|| VWWall wrote:
|| snip
||| Typical values are 220,000 ohms across 470 mfd capacitor charged to
||| about 170 V. This is about 1/8 watt lost in the bleeder resistor.
||| Incidently this is a time constant, (RC), of about 100 seconds. The
||| voltage will drop to 17 V in 2RC or 3 minutes 20 seconds, assuming
||| no other leakage paths.
||
|| You'd be working pretty fast to get the PC opened up, detatch all the
|| power cables, remove the PSU, get it on the workbench and open it up
|| in that time !
|| Pretty safe unless the bleeder resistors have failed.
|
| Yep, agreed. I was just wonderinbg how much power these bleeder
| resistors were wasting while the PSU was running. Not a lot
| obviously. However, it all adds up. 1/8th of a watt per large cap, I
| have five PCs running most of the day (and night). That's gotta be a
| big mac every couple of weeks.

To be honest, unless electricity is very expensive in the opart of the world
where you live, I'd suggest something more like a Big Mac every couple of
years or maybe even a decade.

On Sun, 18 Apr 2004 02:11:08 +1200, "~misfit~"
wrote:

Kevin Lawton wrote:
VWWall wrote:
snip
Typical values are 220,000 ohms across 470 mfd capacitor charged to
about 170 V. This is about 1/8 watt lost in the bleeder resistor.
Incidently this is a time constant, (RC), of about 100 seconds. The
voltage will drop to 17 V in 2RC or 3 minutes 20 seconds, assuming
no other leakage paths.

You'd be working pretty fast to get the PC opened up, detatch all the
power cables, remove the PSU, get it on the workbench and open it up
in that time !
Pretty safe unless the bleeder resistors have failed.

Yep, agreed. I was just wonderinbg how much power these bleeder resistors
were wasting while the PSU was running. Not a lot obviously. However, it all
adds up. 1/8th of a watt per large cap, I have five PCs running most of the
day (and night). That's gotta be a big mac every couple of weeks.

Typical bleeder resistors of hundreds-KOhms are minor waste compared to
even the load resistors inside a power supply, or downclocking the PC by a
few MHz, reducing brightness on monitor a few clicks, etc, etc, etc.

On Sat, 17 Apr 2004 18:22:02 GMT, kony wrote:

Typical bleeder resistors of hundreds-KOhms are minor waste compared to
even the load resistors inside a power supply, or downclocking the PC by a
few MHz, reducing brightness on monitor a few clicks, etc, etc, etc.

Err, that came out a bit backwards... should've been noting the
contrasting energy savings of downclocking or monitor brightness reduction

"CBFalconer" wrote in message
...
Chris Stolworthy wrote:
"Regal" wrote in message

I read on some website that the capacitors in a PC's PSU can
hold a charge for long after they have been switched off and
that the charge could be fatal.

Is this really so? Surely that is exaggerating?

No they are serious, I had the Unfortunate experience not too
long ago of puncturing one on accident. Nasty little shock,
let me tell ya. Some nice electrical burns as well.

We used to take a 200V 0.1 uF capacitor and stick the leads into a
110 V a.c. socket. Everyone knows you can't charge a cap from an
a.c. supply, right? Then hand it to someone to hold. Carefully.


Presumably it depends when you remove it from the AC supply on how
much of a shock you get. If you are lucky you might not get
any shock at all. Unlucky if you get the full 110V. Or 240 in the UK.
Who uses 110V?


--
A: Because it fouls the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

"CBFalconer" wrote in message
...
Chris Stolworthy wrote:
"Regal" wrote in message

I read on some website that the capacitors in a PC's PSU can
hold a charge for long after they have been switched off and
that the charge could be fatal.

Is this really so? Surely that is exaggerating?

No they are serious, I had the Unfortunate experience not too
long ago of puncturing one on accident. Nasty little shock,
let me tell ya. Some nice electrical burns as well.

We used to take a 200V 0.1 uF capacitor and stick the leads into a
110 V a.c. socket. Everyone knows you can't charge a cap from an
a.c. supply, right? Then hand it to someone to hold. Carefully.

Thats quite a good laugh unless you wnd up on a manslaughter charge.


--
A: Because it fouls the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

"Kevin Lawton" wrote in message
...
beav AT wn DoT com DoT au" "beav AT wn DoT com DoT au "beav AT wn DoT
com DoT au" wrote:
| TFM® wrote:
|
|| ThePunisher wrote:
||
||| Regal wrote:
|||
|||| I read on some website that the capacitors in a PC's PSU can hold a
|||| charge for long after they have been switched off and that the
|||| charge could be fatal.
||||
|||| Is this really so? Surely that is exaggerating?
|||
||| You sould check the PSU with a stroboscope before opening it.
||
|| I ain't opening one. I'm a carpenter dammit, not a sparktrician!
|| If a PSU fails, I get another one.
||
|| I got to this age by learning to *heed* warnings.
||
|| TFM®
||
| I open them all the time, to check fuses and remove/replace fans
| etc...

Me too - it is essential maintenance work.
Modern ATX PSUs tend to have temperature controlled fan speed. You
sometimes
find the thermistor used to sense the temperature has been badly
positioned
during assembley - or become displaced - and needs correcting.
Just looked at a PSU and the label says 'Not user serviceable. Only to be
opened by a qualified technician'. Well, I'm qualified in motor vehicle
maintenance and musical instrument repair so that will do just fine. :-)
Kevin.

I trust part of your avanced training told you to remove the PSU from the
mains
before opening the box!