Some switched mode power supplies start by rectifying the mains voltage to
350+volts dc and storing this on a capacitor.That is enough to kill you in
certain circumstances.All capacitors from main powered equipment should be
treated with respect.
Ken Reynolds

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?

"Regal" <(E-Mail Removed)> wrote in message
news:Xns94CCAAEC4846D628D1@208.42.66.156...
> 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?

Isn't that CRT monitors not PC PCUs?
--

Niel Humphreys

Niel Humphreys wrote:
> "Regal" <(E-Mail Removed)> wrote in message
> news:Xns94CCAAEC4846D628D1@208.42.66.156...
>
>>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?
>
> Isn't that CRT monitors not PC PCUs?

Both. They're used in the AC->DC transformer.

--
Paul

"Regal" <(E-Mail Removed)> wrote in message
news:Xns94CCAAEC4846D628D1@208.42.66.156...
> 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.

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.

--
ThePunisher

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?

The capacitors in the input circuit of a PC PSU are charged to
~320 V DC. This can, indeed, be lethal, but they are shunted by
bleeder resistors which will reduce the voltage to a safe value
in a minute or two. By the time you get the unit out of the computer
case and remove it's cover, the voltage is probably safe. To be sure,
wait five minutes after unplugging the PSU before touching anything inside.

A PC monitor uses high voltage, (up to 25,000 V), on the CRT. The tube
glass envelope is used as a capacitor, and can hold a charge for some
time. Because the energy content is quite low, contact with this
very high voltage is usually not deadly, but may result in serious
injury from muscle reaction. Don't remove the housing from a CRT monitor
unless you understand how to safely discharge this voltage!

Virg Wall
--

It is vain to do with more
what can be done with fewer.
William of Occam.

"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?

A well-designed power supply has bleed resistors across the
big capacitors (usually the filtering electrolytics) and the charge
should be essentially dissipated within seconds, certainly a minute,
of shutdown. As for a "fatal" charge, what's the maximum voltage
used in a PC - 12 volts for the fans? Bottom line - have you ever
seen a "Danger! High Voltage" warning on a PC case?

*TimDaniels*

In article <Xns94CCAAEC4846D628D1@208.42.66.156>, "Regal"
(E-Mail Removed) says...
> 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 it is so, no it's not exaggerating. Having said that, I'm still
here so you probably won't kill yourself if you're reasonably careful
and vaguely clueful.

VWWall <(E-Mail Removed)> 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?
>
> The capacitors in the input circuit of a PC PSU are charged to
> ~320 V DC. This can, indeed, be lethal, but they are shunted
> by bleeder resistors which will reduce the voltage to a safe
> value in a minute or two. By the time you get the unit out of
> the computer case and remove it's cover, the voltage is
> probably safe. To be sure, wait five minutes after unplugging
> the PSU before touching anything inside.
>
> A PC monitor uses high voltage, (up to 25,000 V), on the CRT.
> The tube glass envelope is used as a capacitor, and can hold a
> charge for some time. Because the energy content is quite
> low, contact with this very high voltage is usually not
> deadly, but may result in serious injury from muscle reaction.
> Don't remove the housing from a CRT monitor unless you
> understand how to safely discharge this voltage!


Thinkingof power supplies ...

if a faster processor needing extra power was installed (say, it
needs an extra 30 W) then would that noticeably reduce the life of
the power supply?