12v to 5V rails to give 7v for Fan

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

Hi
Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
things to the power supply? I am doing it but I jusy wonder what is
happing in the PSU. Can this be doen with any PSU?

Cheers
Kevin
39 answers Last reply
More about rails give
  1. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    You are about to DESTROY the power supply, and probably your motherboard.
    Where the h*ll did you get this bright idea?

    --
    DaveW


    "Kevin K" <kevin_nzl88@hotmail.com> wrote in message
    news:607636b9.0502112232.b09feef@posting.google.com...
    > Hi
    > Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
    > things to the power supply? I am doing it but I jusy wonder what is
    > happing in the PSU. Can this be doen with any PSU?
    >
    > Cheers
    > Kevin
  2. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    DaveW wrote:

    > You are about to DESTROY the power supply, and probably your motherboard.
    > Where the h*ll did you get this bright idea?
    >

    Who knows where he got the idea from, but if he wants to blow up his
    computer, that's his business, not ours! He's probably got more money
    that he has brains anyway.
  3. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    "Kevin K" <kevin_nzl88@hotmail.com> wrote in message
    news:607636b9.0502112232.b09feef@posting.google.com...
    > Hi
    > Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
    > things to the power supply? I am doing it but I jusy wonder what is
    > happing in the PSU. Can this be doen with any PSU?

    I think this is what you want:
    http://www.heatsink-guide.com/content.php?content=connector.shtml

    It works fine if you don't have the parts to make a speed controller and
    need to cut down the sound your fans make.

    --
    Michael Cecil
    http://home.comcast.net/~macecil/
  4. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    DaveW wrote:
    > You are about to DESTROY the power supply, and probably your motherboard.
    > Where the h*ll did you get this bright idea?
    >

    Oh, for heaven's sake. Connecting a fan from the PSU +12 to +5 for 7 volts
    won't harm a blessed thing.

    Where do YOU get these bright ideas?
  5. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Sat, 12 Feb 2005 16:05:06 -0800, "DaveW" <none@zero.org>
    wrote:

    >You are about to DESTROY the power supply, and probably your motherboard.
    >Where the h*ll did you get this bright idea?

    Possibly hundreds of thousands of people that've been doing
    it for years without incident? It's quite easy to find
    reports, Howtos, etc, about doing it, but quite rare to
    hear of any problems... offhand I don't recall of anyone
    reporting a problem from doing it. I'm not suggesting this
    makes it a good idea though, not with so many other
    alternatives, or even an entirely different (slower) fan
    costing less than $5, OR a faster 12V fan (slowed down by)
    running from 5V.
  6. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <Q5OdnVpI_oozBJPfRVn-2A@comcast.com>, DaveW says...
    > You are about to DESTROY the power supply, and probably your motherboard.
    > Where the h*ll did you get this bright idea?
    >
    Stupid twat.

    How is he going to destroy the PSU?


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  7. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On 11 Feb 2005 22:32:54 -0800, kevin_nzl88@hotmail.com (Kevin K) put
    finger to keyboard and composed:

    >Hi
    >Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
    >things to the power supply? I am doing it but I jusy wonder what is
    >happing in the PSU. Can this be doen with any PSU?
    >
    >Cheers
    >Kevin

    I realise this doesn't answer your question, but someone with a little
    electronics experience may like to build this "efficient fan speed
    controller" using parts from their junk box:
    http://www.siliconchip.com.au/cms/A_103659/article.html

    It can be constructed from an old mobile phone car charger plus an NTC
    resistor and some minor support components. The controller senses the
    case temperature and adjusts the fan speed accordingly.


    - Franc Zabkar
    --
    Please remove one 's' from my address when replying by email.
  8. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    "DaveW" <none@zero.org> wrote in message
    news:Q5OdnVpI_oozBJPfRVn-2A@comcast.com...
    > You are about to DESTROY the power supply, and probably your motherboard.
    > Where the h*ll did you get this bright idea?
    >


    http://www.silentpcreview.com/article6-page1.html

    --
    Derek

    >
    >
    >
    > "Kevin K" <kevin_nzl88@hotmail.com> wrote in message
    > news:607636b9.0502112232.b09feef@posting.google.com...
    >> Hi
    >> Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
    >> things to the power supply? I am doing it but I jusy wonder what is
    >> happing in the PSU. Can this be doen with any PSU?
    >>
    >> Cheers
    >> Kevin
    >
    >
  9. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    >
    >
    > http://www.silentpcreview.com/article6-page1.html
    >
    quote from above link

    "You probably know by now that the standard IDE power connector from
    the power supply contains 2 voltage lines and a third which is derived
    from their difference: 12V, 5V and 7V. Running 7V CAN sometimes be
    potentially stressful for the PSU for technical reasons I won't go
    into here. (It is usually quite safe for a low wattage fan or two, but
    if you want to be perfectly safe, you may want to avoid the 7V tap.)"

    that's what I needed know.

    Anyway I an running my fan/s with a swtich between 5 and 12V and
    dropped the 7V option.

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

    On 11 Feb 2005 22:32:54 -0800, kevin_nzl88@hotmail.com (Kevin K) put
    finger to keyboard and composed:

    >Hi
    >Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
    >things to the power supply? I am doing it but I jusy wonder what is
    >happing in the PSU. Can this be doen with any PSU?
    >
    >Cheers
    >Kevin

    What would happen to the fan's electronics if the +5V rail powered up
    before the +12V rail? There would only be a split second during which
    the fan would be subjected to reverse polarity, but could this be
    harmful?


    - Franc Zabkar
    --
    Please remove one 's' from my address when replying by email.
  11. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    Franc Zabkar wrote:

    > On 11 Feb 2005 22:32:54 -0800, kevin_nzl88@hotmail.com (Kevin K) put
    > finger to keyboard and composed:
    >
    >
    >>Hi
    >>Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
    >>things to the power supply? I am doing it but I jusy wonder what is
    >>happing in the PSU. Can this be doen with any PSU?
    >>
    >>Cheers
    >>Kevin
    >
    >
    > What would happen to the fan's electronics if the +5V rail powered up
    > before the +12V rail? There would only be a split second during which
    > the fan would be subjected to reverse polarity, but could this be
    > harmful?

    That would be potentially a problem for anything connected to both, not
    just a 'fan', and power rails reversing polarity with respect to each other
    is a no-no.

    > - Franc Zabkar
  12. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    says...

    > What would happen to the fan's electronics if the +5V rail powered up
    > before the +12V rail?

    Nothing. It is the same as not being connected on one wire.

    > There would only be a split second during which
    > the fan would be subjected to reverse polarity, but could this be
    > harmful?

    How would it be subjected to reverse polarity? And its a motor...it
    doesn't give a rats arse what way round the polarity is unless its a
    stepper motor which it isn't.


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  13. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <11139bfdcckchc8@corp.supernews.com>, David Maynard says...

    > That would be potentially a problem for anything connected to both, not
    > just a 'fan', and power rails reversing polarity with respect to each other
    > is a no-no.
    >
    What polarity reverse?


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  14. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    Conor wrote:

    > In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    > says...
    >
    >
    >>What would happen to the fan's electronics if the +5V rail powered up
    >>before the +12V rail?
    >
    >
    > Nothing. It is the same as not being connected on one wire.

    No, it's not.


    >>There would only be a split second during which
    >>the fan would be subjected to reverse polarity, but could this be
    >>harmful?
    >
    >
    > How would it be subjected to reverse polarity?

    Because 5 volts being higher than the 12 volt rail is opposite in polarity
    across the fan that if it's less than the 12 volt rail.

    > And its a motor...it
    > doesn't give a rats arse what way round the polarity is unless its a
    > stepper motor which it isn't.

    Not so. It's an electronically driven brushless motor.
  15. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    Conor wrote:
    > In article <11139bfdcckchc8@corp.supernews.com>, David Maynard says...
    >
    >
    >>That would be potentially a problem for anything connected to both, not
    >>just a 'fan', and power rails reversing polarity with respect to each other
    >>is a no-no.
    >>
    >
    > What polarity reverse?
    >
    >

    If 5 is 'higher' than the 12 volt then the polarity across the fan is
    reversed since it should be LOWER than 12 volts.
  16. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <1113p6gd8rdpodc@corp.supernews.com>, David Maynard says...
    > Conor wrote:
    > > In article <11139bfdcckchc8@corp.supernews.com>, David Maynard says...
    > >
    > >
    > >>That would be potentially a problem for anything connected to both, not
    > >>just a 'fan', and power rails reversing polarity with respect to each other
    > >>is a no-no.
    > >>
    > >
    > > What polarity reverse?
    > >
    > >
    >
    > If 5 is 'higher' than the 12 volt then the polarity across the fan is
    > reversed since it should be LOWER than 12 volts.
    >
    Except that there is nothing there so electrically its a non
    connection.


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  17. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <1113pb6820ajb04@corp.supernews.com>, David Maynard says...
    > Conor wrote:
    >
    > > In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    > > says...
    > >
    > >
    > >>What would happen to the fan's electronics if the +5V rail powered up
    > >>before the +12V rail?
    > >
    > >
    > > Nothing. It is the same as not being connected on one wire.
    >
    > No, it's not.
    >
    Unless it has a path to 0V it is.


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  18. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    Conor wrote:
    > In article <1113p6gd8rdpodc@corp.supernews.com>, David Maynard says...
    >
    >>Conor wrote:
    >>
    >>>In article <11139bfdcckchc8@corp.supernews.com>, David Maynard says...
    >>>
    >>>
    >>>
    >>>>That would be potentially a problem for anything connected to both, not
    >>>>just a 'fan', and power rails reversing polarity with respect to each other
    >>>>is a no-no.
    >>>>
    >>>
    >>>What polarity reverse?
    >>>
    >>>
    >>
    >>If 5 is 'higher' than the 12 volt then the polarity across the fan is
    >>reversed since it should be LOWER than 12 volts.
    >>
    >
    > Except that there is nothing there so electrically its a non
    > connection.
    >
    >

    Not so.
  19. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    Conor wrote:

    > In article <1113pb6820ajb04@corp.supernews.com>, David Maynard says...
    >
    >>Conor wrote:
    >>
    >>
    >>>In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    >>>says...
    >>>
    >>>
    >>>
    >>>>What would happen to the fan's electronics if the +5V rail powered up
    >>>>before the +12V rail?
    >>>
    >>>
    >>>Nothing. It is the same as not being connected on one wire.
    >>
    >>No, it's not.
    >>
    >
    > Unless it has a path to 0V it is.

    It has the same kind of 'path to zero' as when the 12 volt rail is higher
    than the 5 volt rail. It's simply reversed (if it happened).
  20. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Tue, 15 Feb 2005 01:31:58 -0600, David Maynard <dNOTmayn@ev1.net>
    put finger to keyboard and composed:

    >Franc Zabkar wrote:
    >
    >> On 11 Feb 2005 22:32:54 -0800, kevin_nzl88@hotmail.com (Kevin K) put
    >> finger to keyboard and composed:
    >>
    >>
    >>>Hi
    >>>Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
    >>>things to the power supply? I am doing it but I jusy wonder what is
    >>>happing in the PSU. Can this be doen with any PSU?
    >>>
    >>>Cheers
    >>>Kevin
    >>
    >>
    >> What would happen to the fan's electronics if the +5V rail powered up
    >> before the +12V rail? There would only be a split second during which
    >> the fan would be subjected to reverse polarity, but could this be
    >> harmful?
    >
    >That would be potentially a problem for anything connected to both, not
    >just a 'fan', and power rails reversing polarity with respect to each other
    >is a no-no.

    I'm not sure what you mean by "power rails reversing polarity with
    respect to each other". I was merely thinking of the situation where
    the +5V rail was at 4V, say, while the +12V rail was still only at 1V,
    if it were possible. This would mean that the fan would see -3V for a
    short time.


    - Franc Zabkar
    --
    Please remove one 's' from my address when replying by email.
  21. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Tue, 15 Feb 2005 09:43:26 -0000, Conor <conor.turton@gmail.com> put
    finger to keyboard and composed:

    >In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    >says...
    >
    >> What would happen to the fan's electronics if the +5V rail powered up
    >> before the +12V rail?
    >
    >Nothing. It is the same as not being connected on one wire.

    Huh?

    >> There would only be a split second during which
    >> the fan would be subjected to reverse polarity, but could this be
    >> harmful?
    >
    >How would it be subjected to reverse polarity? And its a motor...it
    >doesn't give a rats arse what way round the polarity is unless its a
    >stepper motor which it isn't.

    It's a brushless DC motor with an electronic, Hall effect based
    commutator. Do some research before shooting your mouth off. Better
    still, take one apart.


    - Franc Zabkar
    --
    Please remove one 's' from my address when replying by email.
  22. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    Franc Zabkar wrote:

    > On Tue, 15 Feb 2005 01:31:58 -0600, David Maynard <dNOTmayn@ev1.net>
    > put finger to keyboard and composed:
    >
    >
    >>Franc Zabkar wrote:
    >>
    >>
    >>>On 11 Feb 2005 22:32:54 -0800, kevin_nzl88@hotmail.com (Kevin K) put
    >>>finger to keyboard and composed:
    >>>
    >>>
    >>>
    >>>>Hi
    >>>>Does connecting you fans to the 12+ and 5+ to give 7 volts do any bad
    >>>>things to the power supply? I am doing it but I jusy wonder what is
    >>>>happing in the PSU. Can this be doen with any PSU?
    >>>>
    >>>>Cheers
    >>>>Kevin
    >>>
    >>>
    >>>What would happen to the fan's electronics if the +5V rail powered up
    >>>before the +12V rail? There would only be a split second during which
    >>>the fan would be subjected to reverse polarity, but could this be
    >>>harmful?
    >>
    >>That would be potentially a problem for anything connected to both, not
    >>just a 'fan', and power rails reversing polarity with respect to each other
    >>is a no-no.
    >
    >
    > I'm not sure what you mean by "power rails reversing polarity with
    > respect to each other". I was merely thinking of the situation where
    > the +5V rail was at 4V, say, while the +12V rail was still only at 1V,
    > if it were possible. This would mean that the fan would see -3V for a
    > short time.

    When it's 'right' the voltage differential is +7 and the scenario you
    describe put MINUS 3 on it. Going from + to - is a polarity reversal in any
    book, and a no-no.

    +12 is always to be above +5. Otherwise you have a polarity reversal with
    respect to each other.

    >
    >
    > - Franc Zabkar
  23. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Tue, 15 Feb 2005 21:12:28 +1100, Franc Zabkar
    <fzabkar@optussnet.com.au> wrote:


    >>> What would happen to the fan's electronics if the +5V rail powered up
    >>> before the +12V rail? There would only be a split second during which
    >>> the fan would be subjected to reverse polarity, but could this be
    >>> harmful?
    >>
    >>That would be potentially a problem for anything connected to both, not
    >>just a 'fan', and power rails reversing polarity with respect to each other
    >>is a no-no.
    >
    >I'm not sure what you mean by "power rails reversing polarity with
    >respect to each other". I was merely thinking of the situation where
    >the +5V rail was at 4V, say, while the +12V rail was still only at 1V,
    >if it were possible. This would mean that the fan would see -3V for a
    >short time.


    Interesting idea but couldn't we expect the 12V rail to be
    coming up faster because of the amount of capacitance on 5V
    in a PC?
  24. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <d5i311p20dm3nohe55iefs6fd166l1320a@4ax.com>, Franc Zabkar
    says...
    > On Tue, 15 Feb 2005 09:43:26 -0000, Conor <conor.turton@gmail.com> put
    > finger to keyboard and composed:
    >
    > >In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    > >says...
    > >
    > >> What would happen to the fan's electronics if the +5V rail powered up
    > >> before the +12V rail?
    > >
    > >Nothing. It is the same as not being connected on one wire.
    >
    > Huh?
    >
    > >> There would only be a split second during which
    > >> the fan would be subjected to reverse polarity, but could this be
    > >> harmful?
    > >
    > >How would it be subjected to reverse polarity? And its a motor...it
    > >doesn't give a rats arse what way round the polarity is unless its a
    > >stepper motor which it isn't.
    >
    > It's a brushless DC motor with an electronic, Hall effect based
    > commutator. Do some research before shooting your mouth off. Better
    > still, take one apart.
    >
    You've not answered my question. How would it be subjected to reverse
    polarity when it has +5V on one line and in effect N/C on the other?


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  25. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Tue, 15 Feb 2005 15:08:02 GMT, kony <spam@spam.com> wrote:

    >On Tue, 15 Feb 2005 21:12:28 +1100, Franc Zabkar
    ><fzabkar@optussnet.com.au> wrote:
    >
    >
    >>>> What would happen to the fan's electronics if the +5V rail powered up
    >>>> before the +12V rail? There would only be a split second during which
    >>>> the fan would be subjected to reverse polarity, but could this be
    >>>> harmful?
    >>>
    >>>That would be potentially a problem for anything connected to both, not
    >>>just a 'fan', and power rails reversing polarity with respect to each other
    >>>is a no-no.
    >>
    >>I'm not sure what you mean by "power rails reversing polarity with
    >>respect to each other". I was merely thinking of the situation where
    >>the +5V rail was at 4V, say, while the +12V rail was still only at 1V,
    >>if it were possible. This would mean that the fan would see -3V for a
    >>short time.
    >
    >
    >Interesting idea but couldn't we expect the 12V rail to be
    >coming up faster because of the amount of capacitance on 5V
    >in a PC?

    Absolutely, along with the source voltage to the caps being constantly
    more positive on the 12v rail vs the 5v during startup, as both
    circuits are fed from the same transformer. This is verified by this
    schematic of a typical ATX supply:

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

    The presence of R50 on the 5v line should also discharge the 5v rail
    fast enough to keep it negative in relationship to 12v at shutdown
    (depending on the load resistance connected to the 12v rail).

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

    Conor wrote:

    > In article <d5i311p20dm3nohe55iefs6fd166l1320a@4ax.com>, Franc Zabkar
    > says...
    >
    >>On Tue, 15 Feb 2005 09:43:26 -0000, Conor <conor.turton@gmail.com> put
    >>finger to keyboard and composed:
    >>
    >>
    >>>In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    >>>says...
    >>>
    >>>
    >>>>What would happen to the fan's electronics if the +5V rail powered up
    >>>>before the +12V rail?
    >>>
    >>>Nothing. It is the same as not being connected on one wire.
    >>
    >>Huh?
    >>
    >>
    >>>>There would only be a split second during which
    >>>>the fan would be subjected to reverse polarity, but could this be
    >>>>harmful?
    >>>
    >>>How would it be subjected to reverse polarity? And its a motor...it
    >>>doesn't give a rats arse what way round the polarity is unless its a
    >>>stepper motor which it isn't.
    >>
    >>It's a brushless DC motor with an electronic, Hall effect based
    >>commutator. Do some research before shooting your mouth off. Better
    >>still, take one apart.
    >>
    >
    > You've not answered my question. How would it be subjected to reverse
    > polarity when it has +5V on one line and in effect N/C on the other?
    >
    >

    Because it *isn't* a 'N/C' on the other.
  27. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    "Conor" <conor.turton@gmail.com> wrote in message
    news:MPG.1c7be5cd354dfa5c98a02a@news.giganews.com...
    > In article <d5i311p20dm3nohe55iefs6fd166l1320a@4ax.com>, Franc Zabkar
    > says...
    >> On Tue, 15 Feb 2005 09:43:26 -0000, Conor <conor.turton@gmail.com> put
    >> finger to keyboard and composed:
    >>
    >> >In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    >> >says...
    >> >
    >> >> What would happen to the fan's electronics if the +5V rail powered up
    >> >> before the +12V rail?
    >> >
    >> >Nothing. It is the same as not being connected on one wire.
    >>
    >> Huh?
    >>
    >> >> There would only be a split second during which
    >> >> the fan would be subjected to reverse polarity, but could this be
    >> >> harmful?
    >> >
    >> >How would it be subjected to reverse polarity? And its a motor...it
    >> >doesn't give a rats arse what way round the polarity is unless its a
    >> >stepper motor which it isn't.
    >>
    >> It's a brushless DC motor with an electronic, Hall effect based
    >> commutator. Do some research before shooting your mouth off. Better
    >> still, take one apart.
    >>
    > You've not answered my question. How would it be subjected to reverse
    > polarity when it has +5V on one line and in effect N/C on the other?


    Ok, to get 7v you have the 5v rail and 12v rail connected to the fan. (the
    difference between the two gives you 7v to the motor) If the 12v rail were
    to be dropped below the 5v, say to 1v, then you have a reversed polarity.
    That is about as easy as I can explain it. It is DC current, not rocket
    science.

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

    In article <1113pvu8efvcub2@corp.supernews.com>, David Maynard says...
    > Conor wrote:
    >
    > > In article <d5i311p20dm3nohe55iefs6fd166l1320a@4ax.com>, Franc Zabkar
    > > says...
    > >
    > >>On Tue, 15 Feb 2005 09:43:26 -0000, Conor <conor.turton@gmail.com> put
    > >>finger to keyboard and composed:
    > >>
    > >>
    > >>>In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    > >>>says...
    > >>>
    > >>>
    > >>>>What would happen to the fan's electronics if the +5V rail powered up
    > >>>>before the +12V rail?
    > >>>
    > >>>Nothing. It is the same as not being connected on one wire.
    > >>
    > >>Huh?
    > >>
    > >>
    > >>>>There would only be a split second during which
    > >>>>the fan would be subjected to reverse polarity, but could this be
    > >>>>harmful?
    > >>>
    > >>>How would it be subjected to reverse polarity? And its a motor...it
    > >>>doesn't give a rats arse what way round the polarity is unless its a
    > >>>stepper motor which it isn't.
    > >>
    > >>It's a brushless DC motor with an electronic, Hall effect based
    > >>commutator. Do some research before shooting your mouth off. Better
    > >>still, take one apart.
    > >>
    > >
    > > You've not answered my question. How would it be subjected to reverse
    > > polarity when it has +5V on one line and in effect N/C on the other?
    > >
    > >
    >
    > Because it *isn't* a 'N/C' on the other.
    >
    Its not connected to ground so what is it connected to? TBH you're
    arguing the toss about a non issue.


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  29. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <fknQd.7997$ng6.1402@newssvr17.news.prodigy.com>, Ed Medlin
    says...

    > Ok, to get 7v you have the 5v rail and 12v rail connected to the fan. (the
    > difference between the two gives you 7v to the motor) If the 12v rail were
    > to be dropped below the 5v, say to 1v, then you have a reversed polarity.

    No, really?

    > That is about as easy as I can explain it. It is DC current, not rocket
    > science.
    >
    I have 14 years experience as an electronics engineer..I understand
    this.

    However in the real world it'll be ~12V or nothing if it fails. For the
    microsecond its below 5V it isn't going to matter a jot.


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  30. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    Conor wrote:

    > In article <1113pvu8efvcub2@corp.supernews.com>, David Maynard says...
    >
    >>Conor wrote:
    >>
    >>
    >>>In article <d5i311p20dm3nohe55iefs6fd166l1320a@4ax.com>, Franc Zabkar
    >>>says...
    >>>
    >>>
    >>>>On Tue, 15 Feb 2005 09:43:26 -0000, Conor <conor.turton@gmail.com> put
    >>>>finger to keyboard and composed:
    >>>>
    >>>>
    >>>>
    >>>>>In article <uma2119ofc92lrcfcd5db9uescav5laj8s@4ax.com>, Franc Zabkar
    >>>>>says...
    >>>>>
    >>>>>
    >>>>>
    >>>>>>What would happen to the fan's electronics if the +5V rail powered up
    >>>>>>before the +12V rail?
    >>>>>
    >>>>>Nothing. It is the same as not being connected on one wire.
    >>>>
    >>>>Huh?
    >>>>
    >>>>
    >>>>
    >>>>>>There would only be a split second during which
    >>>>>>the fan would be subjected to reverse polarity, but could this be
    >>>>>>harmful?
    >>>>>
    >>>>>How would it be subjected to reverse polarity? And its a motor...it
    >>>>>doesn't give a rats arse what way round the polarity is unless its a
    >>>>>stepper motor which it isn't.
    >>>>
    >>>>It's a brushless DC motor with an electronic, Hall effect based
    >>>>commutator. Do some research before shooting your mouth off. Better
    >>>>still, take one apart.
    >>>>
    >>>
    >>>You've not answered my question. How would it be subjected to reverse
    >>>polarity when it has +5V on one line and in effect N/C on the other?
    >>>
    >>>
    >>
    >>Because it *isn't* a 'N/C' on the other.
    >>
    >
    > Its not connected to ground so what is it connected to?

    And how does connecting the fan to +12 and +5 work when things are normal
    since, according to your logic, it is not "connected to ground?"

    > TBH you're
    > arguing the toss about a non issue.

    I already said it was a non issue because power supplies don't allow it.
  31. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    Conor wrote:

    > In article <fknQd.7997$ng6.1402@newssvr17.news.prodigy.com>, Ed Medlin
    > says...
    >
    >
    >>Ok, to get 7v you have the 5v rail and 12v rail connected to the fan. (the
    >>difference between the two gives you 7v to the motor) If the 12v rail were
    >>to be dropped below the 5v, say to 1v, then you have a reversed polarity.
    >
    >
    > No, really?
    >
    >
    >>That is about as easy as I can explain it. It is DC current, not rocket
    >>science.
    >>
    >
    > I have 14 years experience as an electronics engineer..I understand
    > this.

    Apparently not.


    > However in the real world it'll be ~12V or nothing if it fails. For the
    > microsecond its below 5V it isn't going to matter a jot.

    The power rails are prevented from reversing polarity with each other, that
    is true.

    However, the question was "if it happened" and, if it did, the fan would
    see a reverse polarity.
  32. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Tue, 15 Feb 2005 16:43:30 -0000, Conor
    <conor.turton@gmail.com> wrote:

    >In article <1113p6gd8rdpodc@corp.supernews.com>, David Maynard says...
    >> Conor wrote:
    >> > In article <11139bfdcckchc8@corp.supernews.com>, David Maynard says...
    >> >
    >> >
    >> >>That would be potentially a problem for anything connected to both, not
    >> >>just a 'fan', and power rails reversing polarity with respect to each other
    >> >>is a no-no.
    >> >>
    >> >
    >> > What polarity reverse?
    >> >
    >> >
    >>
    >> If 5 is 'higher' than the 12 volt then the polarity across the fan is
    >> reversed since it should be LOWER than 12 volts.
    >>
    >Except that there is nothing there so electrically its a non
    >connection.

    Nothing where?

    Even if the 12V rail isn't providing 12V, it is providing
    something, a current 'sink if nothing else.
  33. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Tue, 15 Feb 2005 10:57:19 -0800, Michael Thomas
    <mtNOSPAMMING@armory.com> put finger to keyboard and composed:

    >On Tue, 15 Feb 2005 15:08:02 GMT, kony <spam@spam.com> wrote:
    >
    >>On Tue, 15 Feb 2005 21:12:28 +1100, Franc Zabkar
    >><fzabkar@optussnet.com.au> wrote:
    >>
    >>
    >>>>> What would happen to the fan's electronics if the +5V rail powered up
    >>>>> before the +12V rail? There would only be a split second during which
    >>>>> the fan would be subjected to reverse polarity, but could this be
    >>>>> harmful?
    >>>>
    >>>>That would be potentially a problem for anything connected to both, not
    >>>>just a 'fan', and power rails reversing polarity with respect to each other
    >>>>is a no-no.
    >>>
    >>>I'm not sure what you mean by "power rails reversing polarity with
    >>>respect to each other". I was merely thinking of the situation where
    >>>the +5V rail was at 4V, say, while the +12V rail was still only at 1V,
    >>>if it were possible. This would mean that the fan would see -3V for a
    >>>short time.
    >>
    >>
    >>Interesting idea but couldn't we expect the 12V rail to be
    >>coming up faster because of the amount of capacitance on 5V
    >>in a PC?
    >
    >Absolutely, along with the source voltage to the caps being constantly
    >more positive on the 12v rail vs the 5v during startup, as both
    >circuits are fed from the same transformer. This is verified by this
    >schematic of a typical ATX supply:
    >
    >http://www.pavouk.comp.cz/hw/en_atxps.html

    I don't think it's as simple as that. A switchmode PSU has significant
    series inductance at the switchmode frequency which means that the
    voltage at the output does not necessarily follow that at the winding.
    This is the principle behind Vcore regulator circuits such as the
    following (from an M571 socket 7 mainboard):

    ferrite L20
    beads FET coil
    L18 |---| A ===== B to JP8
    +5V o--|--[]-[]--|---------|Q9 |----|---/\/\/---|--o core jumper
    +_|_ +_|_ |-|-| _|_ +_|_
    EC18 ___ ___ EC22 | / \ Q8 ___ EC27
    EC35 | 4000uF | 1500uF | /-|-\ diode | EC32 3500uF
    EC36 _|_ _|_ | _|_ _|_ EC24
    EC21 = = ___|___ = =
    | |
    |KA7500B|
    |_______|

    The voltage at A is a 5Vpp pulse train, while the voltage at B is
    smooth DC, say 2.2V. The L and C components do the smoothing, and the
    KA7500B switchmode regulator varies the pulse width.

    Having said the above, I suspect Kony is right in saying that the +5V
    rail would come up slower due to greater overall capacitance,
    including the capacitance external to the PSU.

    >The presence of R50 on the 5v line should also discharge the 5v rail
    >fast enough to keep it negative in relationship to 12v at shutdown
    >(depending on the load resistance connected to the 12v rail).
    >
    >MT

    The external load would be orders of magnitude greater than the
    internal load, eg 5A compared with 50mA (5V/100R), so R50 would have
    little impact, if any, on the discharge time. In any case, the +12V
    and -12V rails discharge through R51, a 270 ohm resistor, which
    results in a current of 53mA.


    - Franc Zabkar
    --
    Please remove one 's' from my address when replying by email.
  34. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Tue, 15 Feb 2005 16:46:32 -0000, Conor <conor.turton@gmail.com> put
    finger to keyboard and composed:

    >In article <fknQd.7997$ng6.1402@newssvr17.news.prodigy.com>, Ed Medlin
    >says...
    >
    >> Ok, to get 7v you have the 5v rail and 12v rail connected to the fan. (the
    >> difference between the two gives you 7v to the motor) If the 12v rail were
    >> to be dropped below the 5v, say to 1v, then you have a reversed polarity.
    >
    >No, really?
    >
    >> That is about as easy as I can explain it. It is DC current, not rocket
    >> science.
    >>
    >I have 14 years experience as an electronics engineer..

    A board level PC "technician" is not an engineer.

    >I understand
    >this.

    You don't even understand the basic concept of a circuit.

    >However in the real world it'll be ~12V or nothing if it fails. For the
    >microsecond its below 5V it isn't going to matter a jot.

    One microsecond can be a long time, especially for CMOS.


    - Franc Zabkar
    --
    Please remove one 's' from my address when replying by email.
  35. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Thu, 17 Feb 2005 17:42:49 +1100, Franc Zabkar
    <fzabkar@optussnet.com.au> wrote:

    >On Tue, 15 Feb 2005 10:57:19 -0800, Michael Thomas
    ><mtNOSPAMMING@armory.com> put finger to keyboard and composed:
    >
    >>On Tue, 15 Feb 2005 15:08:02 GMT, kony <spam@spam.com> wrote:
    >>
    >>>On Tue, 15 Feb 2005 21:12:28 +1100, Franc Zabkar
    >>><fzabkar@optussnet.com.au> wrote:
    >>>
    >>>
    >>>>>> What would happen to the fan's electronics if the +5V rail powered up
    >>>>>> before the +12V rail? There would only be a split second during which
    >>>>>> the fan would be subjected to reverse polarity, but could this be
    >>>>>> harmful?
    >>>>>
    >>>>>That would be potentially a problem for anything connected to both, not
    >>>>>just a 'fan', and power rails reversing polarity with respect to each other
    >>>>>is a no-no.
    >>>>
    >>>>I'm not sure what you mean by "power rails reversing polarity with
    >>>>respect to each other". I was merely thinking of the situation where
    >>>>the +5V rail was at 4V, say, while the +12V rail was still only at 1V,
    >>>>if it were possible. This would mean that the fan would see -3V for a
    >>>>short time.
    >>>
    >>>
    >>>Interesting idea but couldn't we expect the 12V rail to be
    >>>coming up faster because of the amount of capacitance on 5V
    >>>in a PC?
    >>
    >>Absolutely, along with the source voltage to the caps being constantly
    >>more positive on the 12v rail vs the 5v during startup, as both
    >>circuits are fed from the same transformer. This is verified by this
    >>schematic of a typical ATX supply:
    >>
    >>http://www.pavouk.comp.cz/hw/en_atxps.html
    >
    >I don't think it's as simple as that. A switchmode PSU has significant
    >series inductance at the switchmode frequency which means that the
    >voltage at the output does not necessarily follow that at the winding.
    >This is the principle behind Vcore regulator circuits such as the
    >following (from an M571 socket 7 mainboard):
    >
    > ferrite L20
    > beads FET coil
    > L18 |---| A ===== B to JP8
    > +5V o--|--[]-[]--|---------|Q9 |----|---/\/\/---|--o core jumper
    > +_|_ +_|_ |-|-| _|_ +_|_
    > EC18 ___ ___ EC22 | / \ Q8 ___ EC27
    > EC35 | 4000uF | 1500uF | /-|-\ diode | EC32 3500uF
    > EC36 _|_ _|_ | _|_ _|_ EC24
    > EC21 = = ___|___ = =
    > | |
    > |KA7500B|
    > |_______|
    >

    Nice drawing. A lot of work there.

    >The voltage at A is a 5Vpp pulse train, while the voltage at B is
    >smooth DC, say 2.2V. The L and C components do the smoothing, and the
    >KA7500B switchmode regulator varies the pulse width.
    >

    But do you agree that, regardless of the AC component of the voltages
    across the secondary winding of the transformer T3, the voltage will
    be more positive at the output of rectifier D18 than SBD1 at any given
    moment in time?

    >Having said the above, I suspect Kony is right in saying that the +5V
    >rail would come up slower due to greater overall capacitance,
    >including the capacitance external to the PSU.
    >

    And add the above assertion to the added capacitance and I think you
    can assume that, at least in the case of this supply, the 12v output
    will remain at a more positive potential than the 5v output through
    the startup phase.

    >>The presence of R50 on the 5v line should also discharge the 5v rail
    >>fast enough to keep it negative in relationship to 12v at shutdown
    >>(depending on the load resistance connected to the 12v rail).
    >>
    >>MT
    >
    >The external load would be orders of magnitude greater than the
    >internal load, eg 5A compared with 50mA (5V/100R), so R50 would have
    >little impact, if any, on the discharge time. In any case, the +12V
    >and -12V rails discharge through R51, a 270 ohm resistor, which
    >results in a current of 53mA.
    >

    But wouldn't the current through the 270ohm resister be more like 89mA
    (24v/270R)?

    >
    >- Franc Zabkar
  36. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <kot411lb6pqi5aar28fmg7vkg9icopfjtn@4ax.com>, Franc Zabkar
    says...

    > >I have 14 years experience as an electronics engineer..
    >
    > A board level PC "technician" is not an engineer.
    >
    Of course not. I only worked as an engineer fault finding to component
    level in an industry where chip numbers were routinely scrubbed off and
    custom packages used to prevent copying.


    > >I understand
    > >this.
    >
    > You don't even understand the basic concept of a circuit.
    >
    ROFLMAO...yeah OK. Difference is unlike you I know what happens in the
    real world which tends to not quite mirror whats in books.

    > >However in the real world it'll be ~12V or nothing if it fails. For the
    > >microsecond its below 5V it isn't going to matter a jot.
    >
    > One microsecond can be a long time, especially for CMOS.
    >
    ROFL...

    Give you a hint...try DOING it instead of just reading about it.


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
  37. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Thu, 17 Feb 2005 09:32:15 -0800, Michael Thomas
    <mtNOSPAMMING@armory.com> put finger to keyboard and composed:

    >On Thu, 17 Feb 2005 17:42:49 +1100, Franc Zabkar
    ><fzabkar@optussnet.com.au> wrote:
    >
    >>On Tue, 15 Feb 2005 10:57:19 -0800, Michael Thomas
    >><mtNOSPAMMING@armory.com> put finger to keyboard and composed:
    >>
    >>>On Tue, 15 Feb 2005 15:08:02 GMT, kony <spam@spam.com> wrote:
    >>>
    >>>>On Tue, 15 Feb 2005 21:12:28 +1100, Franc Zabkar
    >>>><fzabkar@optussnet.com.au> wrote:
    >>>>
    >>>>
    >>>>>>> What would happen to the fan's electronics if the +5V rail powered up
    >>>>>>> before the +12V rail? There would only be a split second during which
    >>>>>>> the fan would be subjected to reverse polarity, but could this be
    >>>>>>> harmful?
    >>>>>>
    >>>>>>That would be potentially a problem for anything connected to both, not
    >>>>>>just a 'fan', and power rails reversing polarity with respect to each other
    >>>>>>is a no-no.
    >>>>>
    >>>>>I'm not sure what you mean by "power rails reversing polarity with
    >>>>>respect to each other". I was merely thinking of the situation where
    >>>>>the +5V rail was at 4V, say, while the +12V rail was still only at 1V,
    >>>>>if it were possible. This would mean that the fan would see -3V for a
    >>>>>short time.
    >>>>
    >>>>
    >>>>Interesting idea but couldn't we expect the 12V rail to be
    >>>>coming up faster because of the amount of capacitance on 5V
    >>>>in a PC?
    >>>
    >>>Absolutely, along with the source voltage to the caps being constantly
    >>>more positive on the 12v rail vs the 5v during startup, as both
    >>>circuits are fed from the same transformer. This is verified by this
    >>>schematic of a typical ATX supply:
    >>>
    >>>http://www.pavouk.comp.cz/hw/en_atxps.html
    >>
    >>I don't think it's as simple as that. A switchmode PSU has significant
    >>series inductance at the switchmode frequency which means that the
    >>voltage at the output does not necessarily follow that at the winding.
    >>This is the principle behind Vcore regulator circuits such as the
    >>following (from an M571 socket 7 mainboard):
    >>
    >> ferrite L20
    >> beads FET coil
    >> L18 |---| A ===== B to JP8
    >> +5V o--|--[]-[]--|---------|Q9 |----|---/\/\/---|--o core jumper
    >> +_|_ +_|_ |-|-| _|_ +_|_
    >> EC18 ___ ___ EC22 | / \ Q8 ___ EC27
    >> EC35 | 4000uF | 1500uF | /-|-\ diode | EC32 3500uF
    >> EC36 _|_ _|_ | _|_ _|_ EC24
    >> EC21 = = ___|___ = =
    >> | |
    >> |KA7500B|
    >> |_______|
    >>
    >
    >Nice drawing. A lot of work there.
    >
    >>The voltage at A is a 5Vpp pulse train, while the voltage at B is
    >>smooth DC, say 2.2V. The L and C components do the smoothing, and the
    >>KA7500B switchmode regulator varies the pulse width.
    >>
    >
    >But do you agree that, regardless of the AC component of the voltages
    >across the secondary winding of the transformer T3, the voltage will
    >be more positive at the output of rectifier D18 than SBD1 at any given
    >moment in time?

    Yes.

    >>Having said the above, I suspect Kony is right in saying that the +5V
    >>rail would come up slower due to greater overall capacitance,
    >>including the capacitance external to the PSU.
    >>
    >
    >And add the above assertion to the added capacitance and I think you
    >can assume that, at least in the case of this supply, the 12v output
    >will remain at a more positive potential than the 5v output through
    >the startup phase.

    You're probably right. What got me thinking were the inductances in
    the dotted rectangle, and the size of the loads external to the PSU,
    ie how would the PSU power up if these inductances were significant,
    and if the +12V rail was much more heavily loaded than the +5V rail?
    I'd also been thinking about some mainframe computer PSUs which I
    encountered during the 80's. These would not allow rail A to power up
    if rail B was not operational. I believe this was to protect the many
    RAMs (eg 4116) and EPROMs (eg TMS2516, 2708) which required three
    supply voltages, and which may have been damaged by improper power
    sequencing (???).

    Anyway, I consulted Intel's ATX PSU spec on this issue, but it didn't
    specify the sequencing of the +5V and +12V rails with respect to each
    other, only that both should be always greater than the +3.3V supply.

    ====================================================================
    3.2.10. +5 VDC / +3.3 VDC Power Sequencing

    The +12 VDC and +5 VDC output levels must be equal to or greater than
    the +3.3 VDC output at all times during power-up and normal operation.
    The time between the +12 VDC or +5 VDC output reaching its minimum
    in-regulation level and +3.3 VDC reaching its minimum in-regulation
    level must be <= 20 ms.
    ====================================================================

    >>>The presence of R50 on the 5v line should also discharge the 5v rail
    >>>fast enough to keep it negative in relationship to 12v at shutdown
    >>>(depending on the load resistance connected to the 12v rail).
    >>>
    >>>MT
    >>
    >>The external load would be orders of magnitude greater than the
    >>internal load, eg 5A compared with 50mA (5V/100R), so R50 would have
    >>little impact, if any, on the discharge time. In any case, the +12V
    >>and -12V rails discharge through R51, a 270 ohm resistor, which
    >>results in a current of 53mA.
    >>
    >
    >But wouldn't the current through the 270ohm resister be more like 89mA
    >(24v/270R)?

    You're right. Sorry, brain fart.


    - Franc Zabkar
    --
    Please remove one 's' from my address when replying by email.
  38. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    On Fri, 18 Feb 2005 00:30:55 -0000, Conor <conor@conorturton.com> put
    finger to keyboard and composed:

    >In article <kot411lb6pqi5aar28fmg7vkg9icopfjtn@4ax.com>, Franc Zabkar
    >says...
    >
    >> >I have 14 years experience as an electronics engineer..
    >>
    >> A board level PC "technician" is not an engineer.
    >>
    >Of course not. I only worked as an engineer fault finding to component
    >level in an industry where chip numbers were routinely scrubbed off and
    >custom packages used to prevent copying.

    I've done quite a lot of reverse engineeering myself.

    >> >I understand
    >> >this.
    >>
    >> You don't even understand the basic concept of a circuit.
    >>
    >ROFLMAO...yeah OK. Difference is unlike you I know what happens in the
    >real world which tends to not quite mirror whats in books.

    An electronics engineer with 14 years experience in component level
    troubleshooting is just the kind of person we need at
    sci.electronics.repair. Why don't you drop by and give us the benefit
    of your knowledge? ;-)

    >> >However in the real world it'll be ~12V or nothing if it fails. For the
    >> >microsecond its below 5V it isn't going to matter a jot.
    >>
    >> One microsecond can be a long time, especially for CMOS.
    >>
    >ROFL...

    There is a whole section of the electronics industry devoted to
    transient suppression. Then there are other failure modes such as ESD
    and latchup, either of which can destroy a semiconductor in a fraction
    of a second.

    >Give you a hint...try DOING it instead of just reading about it.

    I've been doing *it* for more than 20 years. I made my living from
    on-site chip-level repairs to minicomputer systems and peripherals,
    both at home and abroad. In those days PCBs contained ~300 chips and
    were expensive (~$10K) to replace, so anyone who could fault find to
    component level, without schematics, could do very well. Since then
    I've been involved in automotive, industrial, and consumer
    electronics, so I believe my exposure to electronics has been fairly
    broad and practical.

    FWIW, I'm a *real* engineer, although I confess that the only benefit
    in my having a degree is that I've never had to worry about not having
    one.


    - Franc Zabkar
    --
    Please remove one 's' from my address when replying by email.
  39. Archived from groups: alt.comp.hardware.homebuilt (More info?)

    In article <as9b1119b3pd7q8qcb0aorkgmafc9e684k@4ax.com>, Franc Zabkar
    says...

    > FWIW, I'm a *real* engineer, although I confess that the only benefit
    > in my having a degree is that I've never had to worry about not having
    > one.
    >
    Ha ha ha...one way of looking at it. Man its nice to see someone with
    the same outlook. I've begun to lose hope that there were still people
    out there who don't actually take what is written in text books as
    gospel. There are lots of things that require the end behaviour of a
    component when not used as its supposed to to get stuff to work. One of
    the first things I was taught to enforce this in the first week was
    building a simple flip-flop circuit using a 4011.


    --
    Conor

    An imperfect plan executed violently is far superior to a perfect plan.
    -- George Patton
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