Capacitors in PSU are dangerous?

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

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.

 

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On Sat, 17 Apr 2004 18:22:02 GMT, kony <spam@spam.com> 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

 

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>| 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.

I'd tend to agree. My calcs suggest it's a fraction of a joule, which is not
even a penny. That's only if you are turning it on and off a lot. There is
some lost through the bleeder resistor while it's on, but that's nothing
compared to the load or inefficiency of the supply.

I added up my boxes use of electricity once. Seems the typical box is < $5 a
month if run 24/7 with the monitor off. Obviously if you have a quad xeon with
a bunch of scsis and huge supply, it's going to be more.

Michael

 

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half_pint <esboella.nospam@yahoo.com> wrote:
<snip>
|| 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!

Eh ? What could I possibley achieve with an unplugged / unpowered open PSU
?
When I open one up it is to fix it and, unless I am replacing the fan, I
need to trace the fault. Just how am I supposed to do that with it switched
off ? I need to run it powered into a dummy load and go round with a DVM
measuring voltages to trace the fault. It might seem a bit old-fashioned,
but at least I can find out what is going on and try to deduce what is
wrong. Sometimes bring an oscilloscope into play as well.
Do you know of any way of fault-tracing a PSU without having it powered up ?
I'd love to know just what it was !
Maybe some strange kind of necromancy or voodoo ? The dead PSUs will once
again inhabit the earth and power their PCs ?
Next time I have a PSU die on me I'll sacrifice a black cockerel - letting
the blood flow onto the body of a naked virgin at the dead of midnight on a
full moon. That should bring it back to life just fine.
Kevin.

 

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"CBFalconer" <cbfalconer@yahoo.com> wrote in message
news:407ECDA4.AF24DD97@yahoo.com...
> Chris Stolworthy wrote:
> > "Regal" <stua_NOTTHISBITsmith@yahoo.co.uk> 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?
>
>

 

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"CBFalconer" <cbfalconer@yahoo.com> wrote in message
news:407ECDA4.AF24DD97@yahoo.com...
> Chris Stolworthy wrote:
> > "Regal" <stua_NOTTHISBITsmith@yahoo.co.uk> 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?
>
>

 

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"Piotr Makley" <pmakley@mail.com> wrote in message
news:94CCB21CBB43A31E75@208.42.66.156...
> VWWall <vwall@DEADearthlink.net> 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?

Actually.... thinking about it..... it may well *increase* the life of the
power supply if the extra load meant the capacitor was not always
fully charged.
What is more likely is your PC would not work and may well have
mysterious reboots (like mine does sometimes) because the
required output voltage cannot be met at peak demand.

The lower the charge on the capacitor the longer it life will be
IIRC.

 

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"VWWall" <vwall@DEADearthlink.net> wrote in message
newsAyfc.11605$k05.8142@newsread2.news.pas.earthlink.net...
> 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.

I don't think that is true, certaintly not if the PSU has a transformer.
The capacitors are on the output side and so I see no reason why they be
charged to more than 12V.

>
> 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.

 

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In article <c5sdef$5ckvt$1@ID-204080.news.uni-berlin.de>,
esboella.nospam@yahoo.com says...
>
> "VWWall" <vwall@DEADearthlink.net> wrote in message
> newsAyfc.11605$k05.8142@newsread2.news.pas.earthlink.net...
> > 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.
>
> I don't think that is true, certaintly not if the PSU has a transformer.
> The capacitors are on the output side and so I see no reason why they be
> charged to more than 12V.
>

The original post mentioning 320V is accurate, though there are some differences
between units that have a 120/240 switch and "full-range" models that don't. You
must be thinking of a transformer input power supply design, where the low voltage
secondary windings are rectified and filtered and regulated. There aren't any PCs
that have supplies of that design because it would be too costly, too large and
too heavy.

PCs have always had line-input switching power supplies, where the AC line is
rectified directly, usually with a voltage doubler when operating from 120V input
and without doubling when running with 220-240VAC input. The nominal 320VDC is
then switched at 20KHz or more to allow use of a much smaller transformer and
smaller filter caps on the many individual outputs.

 

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"VWWall" <vwall@DEADearthlink.net> wrote in message
news:MiCfc.11830$k05.9059@newsread2.news.pas.earthlink.net...
> Piotr Makley wrote:
>
> > VWWall <vwall@DEADearthlink.net> 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?
>
> The main enemy of any electronics is heat. 30W additional output
> means ~10 W additional heat produced in the PSU. Some marginal
> units can't support even their label wattage. It all depends on
> how close to the limit you're pushing the supply. Also the PSU
> fan takes its input air from within the case. This air will be hotter
> due to the 30 additional CPU watts, and without good case ventilation
> will raise the internal temperature of the PS still more.


I think the heat would be generated in the transformer
I am not at all sure any extra heat would be generated (maybe less!!), but
don't
quote me on that.
>
> Virg Wall
> --
>
> It is vain to do with more
> what can be done with fewer.
> William of Occam.

 

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"Kevin Lawton" <kepla@btinternet.com> wrote in message
news:c5sdkc$6o4$1@sparta.btinternet.com...
> half_pint <esboella.nospam@yahoo.com> wrote:
> <snip>
> || 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!
>
> Eh ? What could I possibley achieve with an unplugged / unpowered open
PSU
> ?
> When I open one up it is to fix it and, unless I am replacing the fan, I
> need to trace the fault. Just how am I supposed to do that with it
switched
> off ? I need to run it powered into a dummy load and go round with a DVM
> measuring voltages to trace the fault. It might seem a bit old-fashioned,
> but at least I can find out what is going on and try to deduce what is
> wrong. Sometimes bring an oscilloscope into play as well.
> Do you know of any way of fault-tracing a PSU without having it powered up
?
> I'd love to know just what it was !
> Maybe some strange kind of necromancy or voodoo ? The dead PSUs will once
> again inhabit the earth and power their PCs ?
> Next time I have a PSU die on me I'll sacrifice a black cockerel - letting
> the blood flow onto the body of a naked virgin at the dead of midnight on
a
> full moon. That should bring it back to life just fine.
> Kevin.

I am pretty sure I could trace most faults in a PSU without powering it up.
Your method may be quicker though albeit a little more dangerous.

Presumably your chosen method of sacrifice for the black cockrel is
electrocution?


>
>
>

 

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half_pint <esboella.nospam@yahoo.com> wrote:
| "Kevin Lawton" <kepla@btinternet.com> wrote in message
| news:c5sdkc$6o4$1@sparta.btinternet.com...
|| half_pint <esboella.nospam@yahoo.com> wrote:
|| <snip>
|||| 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!
||
|| Eh ? What could I possibley achieve with an unplugged / unpowered
|| open PSU ?
|| When I open one up it is to fix it and, unless I am replacing the
|| fan, I need to trace the fault. Just how am I supposed to do that
|| with it switched off ? I need to run it powered into a dummy load
|| and go round with a DVM measuring voltages to trace the fault. It
|| might seem a bit old-fashioned, but at least I can find out what is
|| going on and try to deduce what is wrong. Sometimes bring an
|| oscilloscope into play as well.
|| Do you know of any way of fault-tracing a PSU without having it
|| powered up ? I'd love to know just what it was !
|| Maybe some strange kind of necromancy or voodoo ? The dead PSUs
|| will once again inhabit the earth and power their PCs ?
|| Next time I have a PSU die on me I'll sacrifice a black cockerel -
|| letting the blood flow onto the body of a naked virgin at the dead
|| of midnight on a full moon. That should bring it back to life just
|| fine.
|| Kevin.
|
| I am pretty sure I could trace most faults in a PSU without powering
| it up. Your method may be quicker though albeit a little more
| dangerous.
|
| Presumably your chosen method of sacrifice for the black cockrel is
| electrocution?

Well, I don't think I'm risking my life fault tracing on a live PSU, but
would appreciate your insights into unpowered fault finding if you care to
share them.

I'm sure electrocution wouldn't be an adequate sacrificial method, and you
don't get much blood with electrocution - just slight burns.
Blood letting is the way to go with this, using a white-handled knife of
course as resurrecting a PSU is a 'good' purpose.
Hold block cockerel upside-down by the feet, knife to the throat, blood onto
naked virgin, and Robert is one of your parent's siblings.
Just need to find a virgin in time for the next full moon - anyone got one
they can spare ?
Kevin.

 

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"Kevin Lawton" <kepla@btinternet.com> wrote in
news:c5sg00$ekd$1@sparta.btinternet.com:

> Just need to find a virgin in time for the next full moon -
> anyone got one they can spare ?
>

http://www.annwiddecombemp.com/

 

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"Regal" <stua_NOTTHISBITsmith@yahoo.co.uk> 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?


I don't think that is true, certaintly not if the PSU has a transformer.
The capacitors are on the output side and so I see no reason why they be
charged to more than 12V.

So no more dangerous than touching both terminals on a car battery.

However some power supplies may be of a different design and not
use a transformer to step down the voltage.
I don't know how PC PSU's work for sure but I assume they use
a transfromer.

I just had a look and this one does seem to have a capacitor across the
mains supply - so there you go - a little knowledge can be a dangerous
thing!!

Its a czech design though""
http://www.pavouk.comp.cz/hw/en_atxps.html

 

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Archived from groups: alt.comp.hardware.homebuilt (More info?)

>I don't think that is true, certaintly not if the PSU has a transformer.
>The capacitors are on the output side and so I see no reason why they be
>charged to more than 12V.
>

It's linear vs switching power supplies. Totally different design.

Michael

 

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Power supply operating in either 120 VAC or 230 VAC still
charges capacitors up to 320 volts. Anyone with minimal
knowledge of power supplies knows this. One should never
post without first learning basic power supply functions.

Properly posted was that power supplies will have bleed off
resistors on those capacitors. However I have seen power
supplies missing this resistor. In one, the resistor failed.
In another, the resistor was missing. Always use a screw
driver to short out those capacitors before working on a power
supply.

Computer power supplies can hurt you. Now for something
even more dangerous. For the same reason (electrolytic
capacitor), a microwave oven will kill. If that microwave's
bleed off resistor is missing or failed, well, microwave
repairmen have been killed by that missing resistor. Yes -
capacitors inside a power supply can harm humans - despite
posts to the contrary.

How a PC (switching) power supply works: AC mains is
converted to 320 VDC. Then 320 VDC is converted to AC and put
through a tiny transformer. Transformer so small and light
because of how DC is converted to AC. AC voltage output from
transformer converted again back to DC, filtered, monitored,
and then output.

half_pint wrote:
> "Regal" <stua_NOTTHISBITsmith@yahoo.co.uk> 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?
>
> I don't think that is true, certaintly not if the PSU has a
> transformer. The capacitors are on the output side and so I see
> no reason why they be charged to more than 12V.
>
> So no more dangerous than touching both terminals on a car battery.
>
> However some power supplies may be of a different design and not
> use a transformer to step down the voltage.
> I don't know how PC PSU's work for sure but I assume they use
> a transfromer.

 

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"George Pontis" <gpontis@spamcop.net> wrote in message
news:MPG.1aeb5d989a00deac9896b1@news.supernews.com...
> In article <c5sdef$5ckvt$1@ID-204080.news.uni-berlin.de>,
> esboella.nospam@yahoo.com says...
> >
> > "VWWall" <vwall@DEADearthlink.net> wrote in message
> > newsAyfc.11605$k05.8142@newsread2.news.pas.earthlink.net...
> > > 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.
> >
> > I don't think that is true, certaintly not if the PSU has a transformer.
> > The capacitors are on the output side and so I see no reason why they be
> > charged to more than 12V.
> >
>
> The original post mentioning 320V is accurate, though there are some
differences
> between units that have a 120/240 switch and "full-range" models that
don't. You
> must be thinking of a transformer input power supply design, where the low
voltage
> secondary windings are rectified and filtered and regulated. There aren't
any PCs
> that have supplies of that design because it would be too costly, too
large and
> too heavy.
>
> PCs have always had line-input switching power supplies, where the AC line
is
> rectified directly, usually with a voltage doubler when operating from
120V input
> and without doubling when running with 220-240VAC input. The nominal
320VDC is
> then switched at 20KHz or more to allow use of a much smaller transformer
and
> smaller filter caps on the many individual outputs.

Yes point taken, I just had a google on "PC power supplies and I got a bit
of a shock
to see a capacitor across the mains!!
Just as well I as I might have got a more substantial bigger shock by
opening
my PSU to 'have a look inside'. (although I understand there is resistor to
protect
fools like me from themselves!! lol ).

The circuit diagram is 'slightly' more complicated than the one in my
physics
lessons at school where ergonomic factors are ignored.

 

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Kevin Lawton wrote:

> Just need to find a virgin in time for the next full moon - anyone got one
> they can spare ?

The impossible I do at once, miracles take a little longer

Parish

 

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On Sun, 18 Apr 2004 00:07:18 +0100, "half_pint"
<esboella.nospam@yahoo.com> wrote:


>> 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?
>
>Actually.... thinking about it..... it may well *increase* the life of the
>power supply if the extra load meant the capacitor was not always
>fully charged.
>What is more likely is your PC would not work and may well have
>mysterious reboots (like mine does sometimes) because the
>required output voltage cannot be met at peak demand.
>
>The lower the charge on the capacitor the longer it life will be
>IIRC.
>

The short answer is, no.

 

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"Kevin Lawton" <kepla@btinternet.com> wrote in message
news:c5sg00$ekd$1@sparta.btinternet.com...
> half_pint <esboella.nospam@yahoo.com> wrote:
> | "Kevin Lawton" <kepla@btinternet.com> wrote in message
> | news:c5sdkc$6o4$1@sparta.btinternet.com...
> || half_pint <esboella.nospam@yahoo.com> wrote:
> || <snip>
> |||| 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!
> ||
> || Eh ? What could I possibley achieve with an unplugged / unpowered
> || open PSU ?
> || When I open one up it is to fix it and, unless I am replacing the
> || fan, I need to trace the fault. Just how am I supposed to do that
> || with it switched off ? I need to run it powered into a dummy load
> || and go round with a DVM measuring voltages to trace the fault. It
> || might seem a bit old-fashioned, but at least I can find out what is
> || going on and try to deduce what is wrong. Sometimes bring an
> || oscilloscope into play as well.
> || Do you know of any way of fault-tracing a PSU without having it
> || powered up ? I'd love to know just what it was !
> || Maybe some strange kind of necromancy or voodoo ? The dead PSUs
> || will once again inhabit the earth and power their PCs ?
> || Next time I have a PSU die on me I'll sacrifice a black cockerel -
> || letting the blood flow onto the body of a naked virgin at the dead
> || of midnight on a full moon. That should bring it back to life just
> || fine.
> || Kevin.
> |
> | I am pretty sure I could trace most faults in a PSU without powering
> | it up. Your method may be quicker though albeit a little more
> | dangerous.
> |
> | Presumably your chosen method of sacrifice for the black cockrel is
> | electrocution?
>
> Well, I don't think I'm risking my life fault tracing on a live PSU, but
> would appreciate your insights into unpowered fault finding if you care to
> share them.
>
> I'm sure electrocution wouldn't be an adequate sacrificial method, and you
> don't get much blood with electrocution - just slight burns.
> Blood letting is the way to go with this, using a white-handled knife of
> course as resurrecting a PSU is a 'good' purpose.
> Hold block cockerel upside-down by the feet, knife to the throat, blood
onto
> naked virgin, and Robert is one of your parent's siblings.
> Just need to find a virgin in time for the next full moon - anyone got one
> they can spare ?
> Kevin.
>

Well I don't know I am sure a visual inspection would reveal a lot
of faults. Maybe the PSU's you had in mind are a bit more complicated
than the type I was thinking of.. Surely you could test many things using a
lot
lower voltage?
Anyway isn't it more economical just to bin it and put a new PSU in?
When I sent my faulty stereo for repair they just sent me a new one!!
( The new one also had developed a fault within a few weeks, but
cleaning the cd lens appears to have fixed it.).
Both units manufactured by Bush care of Powerhouse. :O) who
incidently went bankrupt voiding my 12 month 'guarantee'.
>
>

 

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Most power supplies are difficult to diagnosis because they
use feedback loops. In a feedback loop, everything looks
defective when only one part has failed.

In one power supply, out of frustration that supply was
winning, I once took the shotgun approach. Removed and tested
every component. Got down to the last few parts when I
discovered an open pull up resistor. Did not even know what
that resistor was doing until I replaced it and monitored. Its
only purpose, to my surprise, was to kick start the circuit
only on power up. Just another reason why power supplies are
so difficult to repair. Some components even have unexpected
surprise functions - as well as located in feedback loops.

A little thing called floating ground. Don't understand it
and vaporize test leads. Many good reasons why they seal up
those power supplies. Power supplies are not so simple.

half_pint wrote:
> Well I don't know I am sure a visual inspection would reveal a lot
> of faults. Maybe the PSU's you had in mind are a bit more complicated
> than the type I was thinking of.. Surely you could test many things
> using a lot lower voltage?
> Anyway isn't it more economical just to bin it and put a new PSU in?
> When I sent my faulty stereo for repair they just sent me a new one!!
> ( The new one also had developed a fault within a few weeks, but
> cleaning the cd lens appears to have fixed it.).
> Both units manufactured by Bush care of Powerhouse. :O) who
> incidently went bankrupt voiding my 12 month 'guarantee'.

 

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"Frank le Spikkin" <zaq@invalid.jp> wrote in message
news:Xns94CFDB81C4CFlSxxx@130.133.1.4...
> "Kevin Lawton" <kepla@btinternet.com> wrote in
> news:c5sg00$ekd$1@sparta.btinternet.com:
>
> > Just need to find a virgin in time for the next full moon -
> > anyone got one they can spare ?
> >
>
> http://www.annwiddecombemp.com/

Those Tories spent their whole lives ****ing people.

 

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half_pint wrote:

>(1) So no more dangerous than touching both terminals on a car battery.
....
>(2) I don't know how PC PSU's work but I assume ...

In a purely technical discussion, I suppose anything goes. But in
safety-related areas where contributions may be read by people without a
technical background, making a statement like (1) in the light of
statement (2) is irresponsible. In fact, making any statement whatsoever
about PSUs in the light of (2) is unjustified.

As it happens, (1) is incorrect. If you, reader, are technically
knowledgeable, judge for yourself whether or not I am right. If you are
not, then play it safe and assume powered-down PSUs to be dangerous.

 

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In article <Xns94CFDB81C4CFlSxxx@130.133.1.4>, Frank le Spikkin
<zaq@invalid.jp> writes
>"Kevin Lawton" <kepla@btinternet.com> wrote in
>news:c5sg00$ekd$1@sparta.btinternet.com:
>
>> Just need to find a virgin in time for the next full moon -
>> anyone got one they can spare ?
>>
>http://www.annwiddecombemp.com/

Euwww! - "Ann coaxes a timid Arbuthnot".
--
Roger Hunt

 

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"Michael Salem" <a$-b$1@ms3.org.uk> wrote in message
news:MPG.1aebde5658f05c9798970f@News.individual.NET...
> half_pint wrote:
>
> >(1) So no more dangerous than touching both terminals on a car battery.
> ...
> >(2) I don't know how PC PSU's work but I assume ...
>
> In a purely technical discussion, I suppose anything goes. But in
> safety-related areas where contributions may be read by people without a
> technical background, making a statement like (1) in the light of
> statement (2) is irresponsible. In fact, making any statement whatsoever
> about PSUs in the light of (2) is unjustified.
>
> As it happens, (1) is incorrect. If you, reader, are technically
> knowledgeable, judge for yourself whether or not I am right. If you are
> not, then play it safe and assume powered-down PSUs to be dangerous.

Hmmm... I don't think that is fair, I did qualify my statement (you snipped
that
out though)
So here it is again

"However some power supplies may be of a different design and not
use a transformer to step down the voltage.
I don't know how PC PSU's work for sure but I assume they use
a transfromer."
"I just had a look and this one does seem to have a capacitor across the
mains supply - so there you go - a little knowledge can be a dangerous
thing!!"

I could quote you out of contest to for example.
"As it happens, (1) is <snip> correct." but its not really fair so I won't.

I also referred to a PSU with the capacitors on the *output* side of
a transformer.

And not all PC PSU's do not uses a mains transformer, certainlty not the
one I am rapidly cobbling togeather ;O)

I did not post as an expert in the field so if you wish to sue me go ahead!

I am sure the lawyers fees will ensure you run out of money before I run out
of
excuses!

half_pint.