Capacitors in PSU are dangerous?

[Guest]

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"Timothy Daniels" <TDaniels@NoSpamDot.com> wrote in message news:<7M6dnc9-QZ8UK-PdRVn-sA@comcast.com>...

> 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

I have a 350W Enermax that was included in an Enermax CS-1251-B case,
and I couldn't find any bleed resistors across those capacitors. I
didn't even see empty spaces where they could have been installed, but
every other PSU I've checked, even some really cheap ones, had those
bleeders. Are bleeders also necessary to help keep the voltages
across the two big capacitors equal, as the capacitors are rarely
rated for even 20% tolerance?

 

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Tim Auton <tim.auton@uton.[groupSexWithoutTheY]> wrote in message news:<m44u7010g87r9jsv82it1mvdupko30eo4n@4ax.com>...
> kony <spam@spam.com> wrote:
> >On Thu, 15 Apr 2004 18:38:30 +0100, Tim Auton

> >It's beyond overkill to advise waiting 24 hours. Even
> >if you didn't know what you were doing you should've
> >known that there's another very obvious way an ATX
> >power supply drains besides the bleeder resistors.
>
> I'm assuming the worst case - ie component failure,
> where the only discharge of the caps is self-discharge.
> In that case though, 24 hours may not be enough. Hmmm,
> I think we need some experimental data.

In February 2003, I charged up a 6,800uF capacitor to 18V. Fourteen
months later, it still measures 12.44V. So I don't think that 24
hours would be enough for an ATX PSU's 1,000uF capacitors to
self-discharge completely in the worst case.

 

[overlord]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

On Fri, 16 Apr 2004 02:04:00 GMT, kony <spam@spam.com> wrote:

>On Fri, 16 Apr 2004 00:11:09 GMT, kurt_SPAMLESS@hotmail.com (Overlord)
>wrote:
>
><snip>
>
>>They also take a finite amount of time to discharge. They can be shorted
>>in such a way to discharge more quickly, kicking out many times their inputted
>>voltage in one great electron orgasm.
>
>A rapid discharge will do nothing to raise the voltage, it's the current
>you're thinking of.... at most the voltage would be the peak input voltage
>(per the input from, position in the circuit, not necessarily the mains AC
>voltage).
>
mmm... RC time constants... yah, current. What I get for taking a break from doing
taxes. Trying to change gears and didn't make it.... Thinking coulombs (Q/T) and
talking volts. But I really don't want to go back to the taxes.....
~~~~~~
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~misfit~ wrote:

> kony wrote:
>
>>On Thu, 15 Apr 2004 14:12:48 -0700, ric <nospam@home.com> wrote:
>>
>>
>>>kony wrote:
>>>
>>>
>>>>>This mustn't be relied on. From my own personal experience (with a
>>>>>monitor): the PSU failed and the monitor died. The cause of the
>>>>>failure was an open-circuit high-value resistor (10 megohms?).
>>>>>This allowed a large capacitor to charge with no discharge path
>>>>>other than leakage. The effect was utterly dead-looking equipment
>>>>>holding a large charge even when switched off.
>>>>
>>>>One difference would be that an ATX power supply is going to
>>>>continue supplying 5VSB, that being another drain.
>>>
>>>The +5vsb typically uses a small bias transformer and is unrelated to
>>>the +300vdc buss. To confirm, monitor the +5vsb while you unplug the
>>>AC cord or switch OFF the rear panel switch. The +5vsb goes away
>>>instantly (or as soon as the +5vsb caps discharge.)
>>
>>It hasn't been unrelated in the units I've traced. They looked
>>pretty standard... right after rectified there was the voltage
>>doubler, the large caps everyone is concerned about, with the
>>bleeder resistors across them, and the power leading to the 5VSB
>>transformer was directly connected, parallel to the bleeder
>>resistors. Perhaps I haven't looked closely enough, at enough
>>different PS 5VSB circuits, but I've not seen anything to suggest any
>>unit deviated from this.
>
>
> So, these bleeder resistors, they're constantly beelding off current, even
> when the machine is in use yes? Sounds wasteful of power to me.

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.

Virg Wall
--

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

 

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ric wrote:

> kony wrote:
>
>
>>>The +5vsb typically uses a small bias transformer and is unrelated to
>>>the +300vdc buss. To confirm, monitor the +5vsb while you unplug the
>>>AC cord or switch OFF the rear panel switch. The +5vsb goes away instantly
>>>(or as soon as the +5vsb caps discharge.)
>>
>>It hasn't been unrelated in the units I've traced. They looked pretty
>>standard... right after rectified there was the voltage doubler, the
>>large caps everyone is concerned about, with the bleeder resistors across
>>them, and the power leading to the 5VSB transformer was directly
>>connected, parallel to the bleeder resistors.
>
>
> The primary of the +5vsb bias transformer connected to a 300VDC source?
> In parallel with the bleed resistors? Poor transformer. Must have HEAVY
> GAUGE windings, or a short life span.

Note kony said "power leading to" transformer. I agree.

See:

http://www.pavouk.comp.cz/hw/en_atxps.html

for an example.

Virg Wall
--

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

 

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VWWall wrote:

> >>It hasn't been unrelated in the units I've traced. They looked pretty
> >>standard... right after rectified there was the voltage doubler, the
> >>large caps everyone is concerned about, with the bleeder resistors across
> >>them, and the power leading to the 5VSB transformer was directly
> >>connected, parallel to the bleeder resistors.
> >
> >
> > The primary of the +5vsb bias transformer connected to a 300VDC source?
> > In parallel with the bleed resistors? Poor transformer. Must have HEAVY
> > GAUGE windings, or a short life span.
>
> Note kony said "power leading to" transformer. I agree.

The circuit at your given URL uses a switching circuit for its +5vsb
output.
The PSUs that I have worked with used a linear circuit for the +5vsb, hence
my use of the term "bias transformer." For the 5-10w of +5vsb, I assumed
most *were* linear. Evidently not.

 

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On Thu, 15 Apr 2004 18:43:06 +0100, Michael Salem <a$-b$1@ms3.org.uk>
put finger to keyboard and composed:

>VWWall wrote:
>>
>> 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.
>
>This mustn't be relied on. From my own personal experience (with a
>monitor): the PSU failed and the monitor died. The cause of the failure
>was an open-circuit high-value resistor (10 megohms?). This allowed a
>large capacitor to charge with no discharge path other than leakage. The
>effect was utterly dead-looking equipment holding a large charge even
>when switched off.

Yes, that's a very common failure mode. These "startup" resistors are
typically of the order of 100K or more. They feed 350V to the base or
gate of the main chopper transistor. If this resistor goes open
circuit, then the PSU doesn't start oscillating, and the main filter
cap doesn't discharge.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

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VWWall <vwall@DEADearthlink.net> 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.
Kevin.

 

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ric <nospam@home.com> wrote:
| kony wrote:
|
||| The +5vsb typically uses a small bias transformer and is unrelated
||| to
||| the +300vdc buss. To confirm, monitor the +5vsb while you unplug the
||| AC cord or switch OFF the rear panel switch. The +5vsb goes away
||| instantly (or as soon as the +5vsb caps discharge.)
||
|| It hasn't been unrelated in the units I've traced. They looked
|| pretty standard... right after rectified there was the voltage
|| doubler, the large caps everyone is concerned about, with the
|| bleeder resistors across them, and the power leading to the 5VSB
|| transformer was directly connected, parallel to the bleeder
|| resistors.
|
| The primary of the +5vsb bias transformer connected to a 300VDC
| source?
| In parallel with the bleed resistors? Poor transformer. Must have
| HEAVY GAUGE windings, or a short life span.

- and pretty useless, too !
A transformer needs AC through its primary windings in order to produce
output. DC will just make it get warm and magnetic.
The big electrolytic capacitors store a charge - from a DC source - and can
then provide a bit of DC as they discharge. Put them across AC and,
depending on the frequency and capacitance, you have a short-circuit or at
least a path of low impedance.
Stick a capacitor and transformer windings in parallel and you will get
either a filter or a tuned circuit - depending on the relative values of
capacitance, inductance and frequency.
Electrolytic capacitors are polarised and should only be used in DC
circuits - the correct way round. Connect them the wrong way, or to AC, and
they are likely to explode.
Kevin.

 

[Guest]

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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?

Capacitors can be dangerous, as any electric shock can be. The danger
depends mainly on the current, and where it is applied. Even a few mA
across the heart can cause an arrest.

Volts, however, is what will give you a decent zap.

The PSU cap charge could be fatal if it discharges through you in the
wrong way. The safest way to deal with these things is to discharge
them with something like a 10MOhm resistor (via insulated probes), and
to wrap wire around the terminals of any you remove.

You're more likely to get your fingers and hand zapped because the
discharge is likely to be localised, but if you really want to kill
yourself, I recommend placing one finger from different hands onto the
terminals of the largest cap you can find, keeping your hands and arms
away from anything which might prevent the discharge from flowing across
your heart.

We routinely wrap wire around the terminals of any capacitor we put into
storage that is larger than, say, a finger. Reason being that these
little electronic b******s manage to magically gain charge from nowhere,
and as you are reaching into the cap drawer to pull out a 470uF for some
job or other, and you brush against the terminals of a 250v 15,000uF
electrolytic, the results can be quite spectacular.

In some of our power supplies, especially the high-current 24v DC ones,
we have some _BIG_ capacitors.... (Think two large cans of dog food
stacked on top of each other)

The other golden rule is DO NOT WORK ON POWER CIRCUITS ALONE. If
someone else is about there are two advantages:
1) You might be able to get them to do it.
2) They may be able to resuscitate you in the event you top yourself

The saying goes
"Beware of the lightning that lurks in an undischarged capacitor lest it
cause thee to be bounced upon thy backside in a most ungainly manner."
(from the Journal of the Rutherford High Energy Laboratory, 31 Jan 1965)

 

[Guest]

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Als wrote:

> I hate to throw another issue into this thread but....everyone seems to have
> an opinion so here is another. Voltage will burn you or your equipment,
> furniture etc. amps will kill. Voltage can knock you off a platform or in
> certain situations kill.

Nope.

One rhyme goes: Volts jolts, mills kills.

You can build up a potential difference of several thousand volts
walking about on a nylon carpet. You then touch a radiator or other
earthed object and get a good zap. The current is miniscule and not
likely to kill you.

However, something that can delivery a lot of current, such as an
undischarged capacitor, mains, or in extreme cases, overhead power
lines, will not only deliver enough current to stop your heart, but
start to cook you through the heating that occurs.

> The hazards are real the warning
> labels are overkill CYA most of the time and common sense is what is needed.

The warning labels are there to try and prevent people with no common
sense from messing with things they don't understand. Take a room with
a hundred typical members of the public in it, and 99 of them will have
no common sense related to electrical matters. The one remaining person
is a doubtful case too.

> I applaud someone just asking a question to find out. By the way I am
> Superintendent of Safety for an Air Force base so I have some knowledge, no
> expert but have researched more injuries than I have suffered by several
> orders of magnitude. LOL

Resarch good. Accidents bad. Research into accidents to prevent
further accidents Better.

 

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larrymoencurly wrote:
>
.... snip ...
>
> In February 2003, I charged up a 6,800uF capacitor to 18V.
> Fourteen months later, it still measures 12.44V. So I don't
> think that 24 hours would be enough for an ATX PSU's 1,000uF
> capacitors to self-discharge completely in the worst case.

That sounds like an outstanding quality cap. I suspect something
else is going on, such as no longer being polarized and thus
having much smaller capacity. If you measure the delta E at some
known current drain you could find out.

--
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?

 

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CBFalconer <cbfalconer@yahoo.com> wrote in message news:<407FCBD0.9B7FD76@yahoo.com>...
> larrymoencurly wrote:

> > In February 2003, I charged up a 6,800uF capacitor to 18V.
> > Fourteen months later, it still measures 12.44V. So I don't
> > think that 24 hours would be enough for an ATX PSU's 1,000uF
> > capacitors to self-discharge completely in the worst case.
>
> That sounds like an outstanding quality cap. I suspect something
> else is going on, such as no longer being polarized and thus
> having much smaller capacity. If you measure the delta E at some
> known current drain you could find out.

It's a blue Sprague, marked 81D, 8939L 3301, 105 Celcius, ripped out
from a trashed circuit board (probably for a burglar or fire alarm).

 

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Parish <me@privacy.net> wrote:
| Kevin Lawton wrote:
|
|| Clint <cneufeld@mysocks.shaw.ca> 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.

 

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"Kevin Lawton" <kepla@btopenworld.com> wrote in
news:c5nbjj$cnd$1@titan.btinternet.com:

>... The wires inside the PC case only carry 3.3v, 5v and
> 12v

<pedantry>
That applies to ATX-style models. AT-style models have a mains power
lead inside the case, for the front panel power switch.
</pedantry>

 

[Guest]

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MCheu wrote:

> As for 12 volts, consider that 12 volts is AFTER the power's been
> adapted from the household outlet power. The household outlets in
> Canada/USA are 120Volts AC, with variable current. Consider that the
> discharge voltage across a capacitor can be many times the charging
> voltage and that it's the current that kills -- and the larger caps in
> a PSU can store, and dump quite a bit of current in a short time or
> store it for days under some conditions.

So it's a bad idea to play with 5 faharad caps then?

--
-Luke-
If cars had advanced at the same rate as Micr0$oft technology, they'd be
flying by now.
But who wants a car that crashes 8 times a day?
Registered Linux User #345134

 

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beav AT wn DoT com DoT au" <"beav AT wn DoT com DoT au <"beav AT wn DoT
com DoT au"> wrote:
| MCheu wrote:
|
|| As for 12 volts, consider that 12 volts is AFTER the power's been
|| adapted from the household outlet power. The household outlets in
|| Canada/USA are 120Volts AC, with variable current. Consider that
|| the discharge voltage across a capacitor can be many times the
|| charging voltage and that it's the current that kills -- and the
|| larger caps in a PSU can store, and dump quite a bit of current in a
|| short time or store it for days under some conditions.
|
| So it's a bad idea to play with 5 faharad caps then?

It all depends on what potential (measured in volts) they are charged up to.
5 Farads is a lot of capacitance, and therefore can hold a lot of charge.
Even charged to only 12 volts, you could probably arc weld with it ! Good
fun to play with - go for it !
Alternatively, dress yourself all in black and chuck one into a crowded lift
(elevator) a shout 'bomb'. Have a camera with you. (only try this in the
absence of security guards). Good fun at airports too.

 

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ric wrote:

> Nice story, but technically flawed. A capacitor will only charge up to
> the peak voltage applied across it. I think you will find that cameras
> use voltage multipliers to achieve their flash voltage, like a small
> fly back circuit or something. [I've never taken one apart, so I don't
> know exactly.]

I have a friend who pulled one apart, mounted it in an empty mobile
phone case, and put 2 nails out the bottom, attached them to the lines
that were connected to the bulb and, well I think you can guess the
rest. We had fun...

--
-Luke-
If cars had advanced at the same rate as Micr0$oft technology, they'd be
flying by now.
But who wants a car that crashes 8 times a day?
Registered Linux User #345134

 

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On Thu, 15 Apr 2004 16:17:25 +0000, VWWall 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.

Further you can generally get them instantly discharged if you are going
to work on them by yanking the power cord, while they are on. They keep
trying to work, and the charge in the capacitor(s)on the line side of the
PSU rapidly discharge.

JAB.

--
Jonathan A. Buzzard Email: jonathan (at) buzzard.me.uk
Northumberland, United Kingdom. Tel: +44 1661-832195

 

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On Fri, 16 Apr 2004 14:28:43 +1200, "~misfit~"
<misfit61nz@yahoomung.co.nz> put finger to keyboard and composed:

>kony wrote:
>> On Thu, 15 Apr 2004 14:12:48 -0700, ric <nospam@home.com> wrote:
>>
>>> kony wrote:
>>>
>>>>> This mustn't be relied on. From my own personal experience (with a
>>>>> monitor): the PSU failed and the monitor died. The cause of the
>>>>> failure was an open-circuit high-value resistor (10 megohms?).
>>>>> This allowed a large capacitor to charge with no discharge path
>>>>> other than leakage. The effect was utterly dead-looking equipment
>>>>> holding a large charge even when switched off.
>>>>
>>>> One difference would be that an ATX power supply is going to
>>>> continue supplying 5VSB, that being another drain.
>>>
>>> The +5vsb typically uses a small bias transformer and is unrelated to
>>> the +300vdc buss. To confirm, monitor the +5vsb while you unplug the
>>> AC cord or switch OFF the rear panel switch. The +5vsb goes away
>>> instantly (or as soon as the +5vsb caps discharge.)
>>
>> It hasn't been unrelated in the units I've traced. They looked
>> pretty standard... right after rectified there was the voltage
>> doubler, the large caps everyone is concerned about, with the
>> bleeder resistors across them, and the power leading to the 5VSB
>> transformer was directly connected, parallel to the bleeder
>> resistors. Perhaps I haven't looked closely enough, at enough
>> different PS 5VSB circuits, but I've not seen anything to suggest any
>> unit deviated from this.
>
>So, these bleeder resistors, they're constantly beelding off current, even
>when the machine is in use yes? Sounds wasteful of power to me.

No, these "bleeder" resistors are of the order of 220K and the caps
are of the order of 470uF. The time constant (RxC) is approx 100 secs,
and the dissipated power is about 300mW. I believe the resistors
perform some kind of "equalisation" function in dual voltage supplies
(110V/240V) that have two filter caps in series. Single cap supplies,
OTOH, have no such resistor.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

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On Thu, 15 Apr 2004 16:48:08 +0100, Regal
<stua_NOTTHISBITsmith@yahoo.co.uk> put finger to keyboard and
composed:

>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?

There are 200V or 400V caps on the primary side of the SMPS. Any
competent tech will discharge these caps before servicing the unit. I
have a load consisting of a 100W 240V lamp which I use for this
purpose.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

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Frank le Spikkin <zaq@invalid.jp> wrote:
| "Kevin Lawton" <kepla@btopenworld.com> wrote in
| news:c5nbjj$cnd$1@titan.btinternet.com:
|
|| ... The wires inside the PC case only carry 3.3v, 5v and
|| 12v
|
| <pedantry>
| That applies to ATX-style models. AT-style models have a mains power
| lead inside the case, for the front panel power switch.
| </pedantry>

Well that's true - - - for many of them.
But then the original IBM PC / AT / XT family had the power switch
protruding out of the side of the PSU and through a hole in the side of the
PC case.
Or the PS/1 which was powered from a PSU in the monitor case.
Or the later PS/2 which had the mains switch integrated in the PSU and
operated by a long push-rod from the front panel.
Not to mention the many Compaq models which had their own 'solution'.
I could go on and on and on . . . . but I wouldn't like to do that
Kevin.

 

[clint]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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" <kepla@btinternet.com> wrote in message
news:c5or19$9c$1@titan.btinternet.com...
> Parish <me@privacy.net> wrote:
> | Kevin Lawton wrote:
> |
> || Clint <cneufeld@mysocks.shaw.ca> 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.
>
>
>

 

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'still right' ? ? ?
Technically correct in that there are high voltages inside a PSU - yes.
But as far as taking the piss 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 <cneufeld@mysocks.shaw.ca> 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" <kepla@btinternet.com> wrote in message
| news:c5or19$9c$1@titan.btinternet.com...
|| Parish <me@privacy.net> wrote:
||| Kevin Lawton wrote:
|||
|||| Clint <cneufeld@mysocks.shaw.ca> 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.

 

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~misfit~ <misfit61nz@yahoomung.co.nz> wrote:
| Kevin Lawton wrote:
|| VWWall <vwall@DEADearthlink.net> 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.