Capacitors in PSU are dangerous?

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

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?
171 answers Last reply
More about capacitors dangerous
  1. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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

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

    Timothy Daniels <TDaniels@NoSpamDot.com> 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?
    |
    | 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?

    You do sometimes see that warning on the PSU !
    A switched-mode power supply works by 'pumping up' capacitors to a high
    voltage with sudden bursts of energy and then regulating the output down to
    the required level, switching the current off and on as needed. Draw more
    current and it uses bigger bursts of energy in each 'pump'. That's why it is
    so efficient in size terms. If you were using a linear power supply to
    supply the currents used inside a modern PC it would be far bigger and
    dissipate a lot more heat.
    Under normal circumstances, the bleed resistors should do their job - but
    you wouldn't open up the PSU under normal circumstances would you ? Under
    fault conditions - what if a bleed resistor has failed ?
    Kevin.
  4. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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

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

    Timothy Daniels 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?

    That's a maximum *external* voltage. The OP asked about *internal*
    voltages.
    The 300vdc buss charges to the peak value of the AC input sine wave (times
    2 in the U.S.) or 132 * 1.414 * 2 = 373vdc max (typically 330-340 volts.)
    That's enough to give a nasty jolt. The amount of this charge left over
    time depends on, of course, the size of the capacitors and the bleed
    resistors (if any) in parallel with them.
  7. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "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?

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

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

    Niel Humphreys 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?
    >
    > Isn't that CRT monitors not PC PCUs?

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

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

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

    In article <c5mfs7$3etsj$1@ID-206197.news.uni-berlin.de>,
    Parish <me@privacy.net> 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.
    >>

    >ROFLMAO :-)


    You have to leave the 'scope attached for 24 hours to get a valid
    reading ;-)
    --
    Al Dykes
    -----------
    adykes at p a n i x . c o m
  11. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    In article <Xns94CCAAEC4846D628D1@208.42.66.156>, "Regal"
    stua_NOTTHISBITsmith@yahoo.co.uk 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.
  12. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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

    "ThePunisher" <thepunisher@ntlworld.com> 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.

    Eh?


    Tim
    --
    Love is a travelator.
  14. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
    news:itet705nu64c644sobf9pa1antd4usia90@4ax.com...
    > "ThePunisher" <thepunisher@ntlworld.com> 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.
    >
    > Eh?
    >
    >
    > Tim
    > --
    > Love is a travelator.

    The stroboscope is effective only as long as the PSU is spinning or
    vibrating rapidly. Or if you are hallucinating that it is...
    --
    John McGaw
    [Knoxville, TN, USA]
    http://johnmcgaw.com
  15. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "Timothy Daniels" <TDaniels@NoSpamDot.com> 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?
    >
    > 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?

    The maximum voltage inside a PSU is the mains of course!

    They should have bleeder resistors, but that doesn't mean they all do.
    When giving advice to people of undetermined ability and experience on
    usenet I think it's safest to assume the PSU is badly designed and
    will potentially hold dangerous voltages for some time after it's
    unplugged.

    If someone is sufficiently lacking in knowledge to have to ask the
    question they should assume that *every* part of the inside of their
    PSU is lethal for 24 hours after it's unplugged.


    Tim
    --
    Love is a travelator.
  16. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    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.
    >

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

    "Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
    news:11ft705ehj55au54lu1gd0ob90frda1af3@4ax.com...
    | "Timothy Daniels" <TDaniels@NoSpamDot.com> 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?
    | >
    | > 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?
    |
    | The maximum voltage inside a PSU is the mains of course!
    |
    | They should have bleeder resistors, but that doesn't mean they all do.
    | When giving advice to people of undetermined ability and experience on
    | usenet I think it's safest to assume the PSU is badly designed and
    | will potentially hold dangerous voltages for some time after it's
    | unplugged.
    |
    | If someone is sufficiently lacking in knowledge to have to ask the
    | question they should assume that *every* part of the inside of their
    | PSU is lethal for 24 hours after it's unplugged.
    |
    Bollox !
  18. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    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?


    Not sure what voltages the caps in a PC PSU would reach, but in general
    those caps can be dangerous because, once charged, they can deliver very
    high currents for short durations - enough to get some spectacular
    fireworks, burn things to ashes etc.
  19. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "DCA" <MAPSdca860@MAPSntlworld.com> wrote:
    >"Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
    >news:11ft705ehj55au54lu1gd0ob90frda1af3@4ax.com...
    [snip]
    >| The maximum voltage inside a PSU is the mains of course!
    >|
    >| They should have bleeder resistors, but that doesn't mean they all do.
    >| When giving advice to people of undetermined ability and experience on
    >| usenet I think it's safest to assume the PSU is badly designed and
    >| will potentially hold dangerous voltages for some time after it's
    >| unplugged.
    >|
    >| If someone is sufficiently lacking in knowledge to have to ask the
    >| question they should assume that *every* part of the inside of their
    >| PSU is lethal for 24 hours after it's unplugged.
    >|
    >Bollox !

    You feel free to advise people to do whatever you like, but some
    people prefer to advise people of undetermined ability to err on the
    side of caution.

    Do I wait? No. But then I know what I'm doing.


    Tim
    --
    Love is a travelator.
  20. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    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.

    > 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!

    A common way of taking advantage of the extra-high-tension available in
    a television set was to make an arc to earth and use it to light
    cigarettes. This was in valve days; don't try it with semiconductor EHT
    rectifiers with low impedance, as it'll fry them.

    Best wishes,
    --
    Michael Salem
  21. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    In article <407EC5E0.7020407@dsl.pipex.com>, Martin Slaney
    <slazNIET_SPAM@dsl.pipex.com> writes
    >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?
    >
    >
    >Not sure what voltages the caps in a PC PSU would reach, but in general
    >those caps can be dangerous because, once charged, they can deliver very
    >high currents for short durations - enough to get some spectacular
    >fireworks, burn things to ashes etc.
    >
    It would seem to me that the safest thing to do would be to don wellies
    and hose the system down with water before touching anything.
    --
    Roger Hunt
  22. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    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.

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

    On Thu, 15 Apr 2004 17:30:32 +0100, Piotr Makley <pmakley@mail.com> wrote:


    >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?

    Generally no, it would be a progressively shorter lifespan but even so
    there are other factors that could decrease lifespan or cause failure
    before that became significant.

    On the other hand, if the power supply can't maintain the additional load
    it may cause a lot of additional ripple which is harder on the
    motherboard.

    Rather than looking at the incremental wattage increase a determination
    should be made of the total system power usage... not necessarily an exact
    figure but in the ballpark, then using a quality name-brand unit so at
    least there's some assurance it's capable of wattage stamped on it's
    label.
  24. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    On Thu, 15 Apr 2004 18:43:06 +0100, Michael Salem <a$-b$1@ms3.org.uk>
    wrote:

    >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.

    One difference would be that an ATX power supply is going to continue
    supplying 5VSB, that being another drain.
  25. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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

    On Thu, 15 Apr 2004 18:38:30 +0100, Tim Auton
    <tim.auton@uton.[groupSexWithoutTheY]> wrote:


    >You feel free to advise people to do whatever you like, but some
    >people prefer to advise people of undetermined ability to err on the
    >side of caution.
    >
    >Do I wait? No. But then I know what I'm doing.

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

    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.

    Virg Wall
    --

    It is vain to do with more
    what can be done with fewer.
    William of Occam.
  28. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    Hello

    "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 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. Pacemaker comes to mind and certain heart
    conditions. Why do I say this OSHA electrical safety course among many
    others. I haven't looked at PSU for their specs but I do believe that common
    sense will keep you safe be it voltage current/amps or what ever. Yes I know
    that amps are related to watts and voltage but that is dependent on
    resistance. Here is link to some terms and guidance. To many issues to
    address in a limited time but the hazards are more than what will kill you.
    Fire, Shock and death being the 3 foremost. The hazards are real the warning
    labels are overkill CYA most of the time and common sense is what is needed.
    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

    Something to think about:
    Good judgment come from experience, experience well that comes from bad
    judgment.
    If you don't like that quote here is an original.
    Stupid should be painful its up to you if its Motrin or morphine. Ask the
    question!

    http://www.utsa.edu/compliance/enviro/Section%2004/Sec04-01.html
  29. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    Kevin Lawton wrote:

    > Timothy Daniels <TDaniels@NoSpamDot.com> 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?
    > |
    > | 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?
    >
    > You do sometimes see that warning on the PSU !
    > A switched-mode power supply works by 'pumping up' capacitors to a high
    > voltage with sudden bursts of energy and then regulating the output down to
    > the required level, switching the current off and on as needed. Draw more
    > current and it uses bigger bursts of energy in each 'pump'. That's why it is
    > so efficient in size terms. If you were using a linear power supply to
    > supply the currents used inside a modern PC it would be far bigger and
    > dissipate a lot more heat.

    Close, but no cigar! There is no "pumping" of the input capacitors. They
    are either charged to the peak line voltage from a 240 V line input, or they
    are charged with a voltage doubler rectifier circuit from a 120 V line input.
    The approximately 340 V DC derived is then switched at a rate of about 50,000
    cycles and then transformed down to the desired output voltages. The time
    the "switch" is on determines the output voltages, and PWM (pulse width
    modulation) is used to regulate these voltages. The main reduction in
    size is due to the small core needed for the output transformer. In addition,
    the input transformer is eliminated completely.

    > Under normal circumstances, the bleed resistors should do their job - but
    > you wouldn't open up the PSU under normal circumstances would you ? Under
    > fault conditions - what if a bleed resistor has failed ?

    The most frequent reason I have opened a PSU is to replace the fan. Even
    with a failed bleeder there is enough leakage current to discharge the
    capacitors in less than the "many hours" often quoted. If you're really
    worried, let the supply remain un-plugged overnight. Then be very careful
    not to cut yourself on the sharp metal edges in most PSUs! ;)

    Virg Wall
    --

    It is vain to do with more
    what can be done with fewer.
    William of Occam.
  30. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    kony wrote:

    > On Thu, 15 Apr 2004 18:43:06 +0100, Michael Salem <a$-b$1@ms3.org.uk>
    > wrote:
    >
    >
    >>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.
    >
    >
    > One difference would be that an ATX power supply is going to continue
    > supplying 5VSB, that being another drain.

    Also the main switching supply will continue to operate until the capacitors
    are down to <~ 250 V, still more drain. With the excption of those PSUs
    that have heat sinks at an input voltage potential, it's very hard to
    get even your finger tips on the full voltage. A little care is still
    advised.

    Virg Wall
    --

    It is vain to do with more
    what can be done with fewer.
    William of Occam.
  31. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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

    VWWall wrote:

    > Also the main switching supply will continue to operate until the capacitors
    > are down to <~ 250 V, still more drain.

    Not ATX PSUs. The switching circuitry is inhibited as soon as the
    PS_ON signal goes high. If the PSU is under light load, the 300v
    buss could still be well over 300vdc.
  33. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    True.

    --
    DaveW


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

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

    kony <spam@spam.com> wrote:
    >On Thu, 15 Apr 2004 18:38:30 +0100, Tim Auton
    ><tim.auton@uton.[groupSexWithoutTheY]> wrote:
    >
    >>You feel free to advise people to do whatever you like, but some
    >>people prefer to advise people of undetermined ability to err on the
    >>side of caution.
    >>
    >>Do I wait? No. But then I know what I'm doing.
    >
    >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.


    Tim
    --
    Love is a travelator.
  36. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    >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'd tend to agree, esp. with switched mode supplies. Even powerful audio amps
    with linear or switching supplies can be potentially dangerous. Old CRT's are
    dangerous, possibly newer ones as well.

    I work on all this stuff occasionally, but I take precautions. I try to use
    one hand only, which avoids a circuit across the heart.

    There should be bleeder resistors that will leak off the charge eventually.
    You can also make a shorting rod and discharge them before repairs.

    I'm just a hobbyist / low voltage tech, not a high-voltage tech, but I can't
    recall anyone dying from servicing a home computer. There have certainly been
    a few deaths among hams servicing 2kw homebrew amps. Generally among older
    persons, but it's enough juice to kill younger guys too.

    Obviously i am talking about _unplugged_ gear, I hope this goes without saying.

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

    Under the right<?> circumstances yes.
    Your UK voltage is like 230volts? That's the rms value, like an average
    effective value. The peak value would be 325 volts then.
    Also, the capacitors take a finite amount of time to charge up in a circuit.
    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.

    You have a camera?
    You push the button half way and see the little blinking light; it's charging a capacitor.
    The light goes steady; the capacitor is charged.
    You push the button the rest of the way in and it discharges in a smaller time constant
    to flash the flash bulb. Those itty bitty batteries in the camera can't flash it on their output
    voltage on their own. The discharge is many times the voltage that the battery slowly put
    into the capacitor. If those little 1.5volt (or whatever) batteries can charge that capacitor
    to discharge and flash that flashbulb, think what a nice flash you can get from discharging
    the capacitor that you charged with the 230volt line current, properly or improperly
    handled....

    You probably won't light up like a flash bulb.... but you'll think you did.


    On Thu, 15 Apr 2004 16:48:08 +0100, Regal <stua_NOTTHISBITsmith@yahoo.co.uk> 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?

    ~~~~~~
    Bait for spammers:
    root@localhost
    postmaster@localhost
    admin@localhost
    abuse@localhost
    postmaster@[127.0.0.1]
    uce@ftc.gov
    ~~~~~~
    Remove "spamless" to email me.
  38. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    Overlord wrote:

    > Under the right<?> circumstances yes.
    > Your UK voltage is like 230volts? That's the rms value, like an average
    > effective value. The peak value would be 325 volts then.
    > Also, the capacitors take a finite amount of time to charge up in a circuit.
    > 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.

    Many times their charging *current*? Yes.
    Many times their charging *voltage*? No.

    > You have a camera?
    > You push the button half way and see the little blinking light; it's charging a capacitor.
    > The light goes steady; the capacitor is charged.
    > You push the button the rest of the way in and it discharges in a smaller time constant
    > to flash the flash bulb. Those itty bitty batteries in the camera can't flash it on their output
    > voltage on their own. The discharge is many times the voltage that the battery slowly put
    > into the capacitor. If those little 1.5volt (or whatever) batteries can charge that capacitor
    > to discharge and flash that flashbulb, think what a nice flash you can get from discharging
    > the capacitor that you charged with the 230volt line current, properly or improperly
    > handled....

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

    >The capacitors in the input circuit of a PC PSU are charged to
    >~320 V DC.

    Most home DMM's measure to 2k volts. So you can easily test the circuit before
    putting your hands in there.

    Obviously that may not work on CRT's and TV's. :-)

    I picked up a TV repair manual for 5 bucks used. Had plenty of tips on working
    with high-voltage circuits. Should be plenty of stuff available at the local
    library. A little reading may save your life.

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

    >The main enemy of any electronics is heat. 30W additional output
    >means ~10 W additional heat produced in the PSU.

    Are you sure? I'd believe that ratio in a linear supply, but in a switching
    supply?

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

    jealous xmp wrote:

    > >The main enemy of any electronics is heat. 30W additional output
    > >means ~10 W additional heat produced in the PSU.
    >
    > Are you sure? I'd believe that ratio in a linear supply, but in a switching
    > supply?

    Being that switching PSUs used in PCs are typically 70-75% efficient,
    yeah - that sounds right. 40w more input, 30w more output, 10w more heat.
    That would be 75% efficiency.

    Now, how well that heat is dealt with....*that* is the big question.
  42. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    VWWall <vwall@DEADearthlink.net> wrote:

    > Close, but no cigar! There is no "pumping" of the input
    > capacitors. They are either charged to the peak line voltage
    > from a 240 V line input, or they are charged with a voltage
    > doubler rectifier circuit from a 120 V line input. The
    > approximately 340 V DC derived is then switched at a rate of
    > about 50,000 cycles and then transformed down to the desired
    > output voltages. The time the "switch" is on determines the
    > output voltages, and PWM (pulse width modulation) is used to
    > regulate these voltages. The main reduction in size is due to
    > the small core needed for the output transformer. In
    > addition, the input transformer is eliminated completely.

    As a related aside ....

    I think those room light dimmers (for normal incandescent bulbs)
    work in a similar way to the way you describe for a switched mode
    PSU. In other words chopping up the output voltage into very small
    slices.

    Would such a device set to "dim" register less on the household
    electric meter than when set to "bright"?
  43. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    Piotr Makley wrote:

    > VWWall <vwall@DEADearthlink.net> wrote:
    >
    >
    >>Close, but no cigar! There is no "pumping" of the input
    >>capacitors. They are either charged to the peak line voltage
    >>from a 240 V line input, or they are charged with a voltage
    >>doubler rectifier circuit from a 120 V line input. The
    >>approximately 340 V DC derived is then switched at a rate of
    >>about 50,000 cycles and then transformed down to the desired
    >>output voltages. The time the "switch" is on determines the
    >>output voltages, and PWM (pulse width modulation) is used to
    >>regulate these voltages. The main reduction in size is due to
    >>the small core needed for the output transformer. In
    >>addition, the input transformer is eliminated completely.
    >
    >
    > As a related aside ....
    >
    > I think those room light dimmers (for normal incandescent bulbs)
    > work in a similar way to the way you describe for a switched mode
    > PSU. In other words chopping up the output voltage into very small
    > slices.

    They are similar except they work directly with the AC voltage. When
    set to "dim" they let less than the full half of the sinewave AC in each
    direction through to the lamp. The thermal lag of the lamp filament filters
    out the short "pulses" and the lamp produces less light. The PDM switch
    in a PSU works with DC voltage of both polarities and is switched at
    a high (~50 KHz) frequency. This produces a waveform the output transformer
    can handle. At the high frequency the core can be much smaller than a
    transformer working at line (50/60 Hz) frequency. The efficiency is also
    much higher since the transistor switches are either on or off and don't
    dissipate much power internally in either state.
    >
    > Would such a device set to "dim" register less on the household
    > electric meter than when set to "bright"?

    Yes. The electric meter is an integrating device. Less total energy flow
    when the lamps are on dim equals less energy registered.

    Virg Wall
    --

    It is vain to do with more
    what can be done with fewer.
    William of Occam.
  44. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    >Close, but no cigar! There is no "pumping" of the input capacitors. They
    >are either charged to the peak line voltage from a 240 V line input, or they
    >are charged with a voltage doubler rectifier circuit from a 120 V line input.

    I could see how the voltages could get high. It's 120 volts, but that's RMS.
    Each alternating dip is 170 volts peak. And 170*2 would be 340 volts (doubling
    circuit).

    A doubling or quadrupling circuit could be viewed as "pumping" IMHO.

    FWIW, anything over 14 volts is generally referred to as dangerous. I've built
    small supplies and I personally wouldn't put my hands across a +/- 30 volts.

    Even the low current 90 volts of a phone circuit (it was ringing) gave me a
    jolt once.

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

    >The maximum voltage inside a PSU is the mains of course!

    I haven't looked at the schematics of PC PSU lately, but it would depend on the
    circuit. There may be a doubling circuit as someone noted, for use in US as
    well as Europe's higher rails.

    You can't say definitively say that the PSU is at mains voltage peak. 170 to
    340 volts is my best guess. I'd have to see the specific circuit. Don't
    forget all voltages are 50 percent higher potentially due to the mains being
    rated in RMS, not peak or peak-to-peak.

    In the end, the voltage perhaps isn't the only factor. The capacitors would
    vary from supply to supply and determine the upper bound of energy stored by
    the cap.

    Q=CV

    The couloumbs of charge is just capacitance times voltage. I believe the
    energy would be 1/2CV^2. So the energy is proportional to capacitance, but the
    square of the voltage.

    In the end, that energy and charge determine the current and time across the
    body during it's discharge phase.

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

    >They are similar except they work directly with the AC voltage. When
    >set to "dim" they let less than the full half of the sinewave AC in each
    >direction through to the lamp. The thermal lag of the lamp filament filters
    >out the short "pulses" and the lamp produces less light.

    Some of the old dimmers were just a thyristor like a triac in the circuitry.
    The "gate" voltage would determine when it "tripped." Thus the output is a
    chopped up waveform, which lowers the average energy emitted by the element in
    the bulb.

    I believe this is why the dimmers and related stuff sometimes cause a visible
    flashing.

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

    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.

    --
    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?
  48. 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 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).
  49. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    ric <nospam@home.com> wrote in message news:<407EFAD0.A2AF5241@home.com>...
    > 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.)

    I checked some +5Vstandby circuits because I wanted to know why the
    one in my Raidmax/Powmax had a much smaller transformer than the
    others, and I found that they didn't use separate capacitors but were
    powered from the same big ones that ran the main PSU. Most even ran
    the +5Vstandby transformer at exactly the same frequency, although
    Enermax used 2x and Raidmax/Powmax used 4x. The one exception may have
    been a super-cheap 250W (PC Power & Cooling shows it as an example of
    a bad PSU) where the +5Vstandby circuit was held on a completely
    separate circuit board, but I don't really remember.
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