Can Low Voltage kill a power supply?

Discussion in 'DIY PC' started by n33ck0@gmail.com, Aug 19, 2006.

  1. Guest

    Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    neighborhood. After calling the utility co. it was determined there was
    too much demand on the grid. not anything specific in the house. So
    here is my question can a low voltage situation kill a computer power
    supply. Taking in account it is not a cheap one: I paid over $75.00US
    when new its rated @ 500w and it never gave me a problem before. Also
    its strange because the PS on a compaq desktop I also have didn't even
    flinch. Nothing else got burned or failed in my house. I know all
    components in that particular PC are good 'cause I tested it with
    another PS. Thanks Also is there any way I can check if is still good?
     
    , Aug 19, 2006
    #1
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  2. Rod Speed Guest

    wrote:

    > Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    > neighborhood. After calling the utility co. it was determined there
    > was too much demand on the grid. not anything specific in the house.
    > So here is my question can a low voltage situation kill a computer power supply.


    A properly designed power supply should shut down in that situation.

    A badly designed power supply can be killed in that situation.

    > Taking in account it is not a cheap one: I paid over $75.00US when
    > new its rated @ 500w and it never gave me a problem before.


    The price doesnt mean a lot on that basic design question.

    > Also its strange because the PS on a compaq
    > desktop I also have didn't even flinch.


    Yeah, a properly designed power supply wont turn a hair.

    > Nothing else got burned or failed in my house. I know all components
    > in that particular PC are good 'cause I tested it with another PS.


    Thats all the evidence you need that its dead.

    > Thanks Also is there any way I can check if is still good?


    You just did.
     
    Rod Speed, Aug 19, 2006
    #2
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  3. Guest

    Rod Speed wrote:
    > wrote:
    >
    > > Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    > > neighborhood. After calling the utility co. it was determined there
    > > was too much demand on the grid. not anything specific in the house.
    > > So here is my question can a low voltage situation kill a computer power supply.

    >
    > A properly designed power supply should shut down in that situation.
    >
    > A badly designed power supply can be killed in that situation.
    >
    > > Taking in account it is not a cheap one: I paid over $75.00US when
    > > new its rated @ 500w and it never gave me a problem before.

    >
    > The price doesnt mean a lot on that basic design question.
    >
    > > Also its strange because the PS on a compaq
    > > desktop I also have didn't even flinch.

    >
    > Yeah, a properly designed power supply wont turn a hair.
    >
    > > Nothing else got burned or failed in my house. I know all components
    > > in that particular PC are good 'cause I tested it with another PS.

    >
    > Thats all the evidence you need that its dead.
    >
    > > Thanks Also is there any way I can check if is still good?

    >
    > You just did.


    Thank You Sir!. Suspicions confirmed.
     
    , Aug 19, 2006
    #3
  4. "Rod Speed" <> wrote in message
    news:...
    > wrote:
    >
    >> Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    >> neighborhood. After calling the utility co. it was determined there
    >> was too much demand on the grid. not anything specific in the house.
    >> So here is my question can a low voltage situation kill a computer power
    >> supply.

    >
    > A properly designed power supply should shut down in that situation.
    >
    > A badly designed power supply can be killed in that situation.
    >


    Just a bit curious as to how you think a power supply can be damaged by a
    low voltage situation?

    Since all the regulation in a PS is designed to convert AC to DC and then
    regulate those output voltages down to useable levels within a specified
    tolerance I don't see how a low voltage could result in a dead PS. I DO see
    how it can cause flakiness on the low voltage side since all outputs are
    based upon a properly regulated input voltage tolerance, but all that should
    result from a low input voltage is proportionally low output voltages.

    Personally I would think that most of the damage would have been caused by a
    backlash of higher voltage that can often occur after low voltage
    situations. This higher than normal voltage inrush could happen faster than
    the regulators are prepared to handle and cause a very quick spike to get
    through the filters and fry the lower voltage side of the regulation circuit
    perhaps.
     
    Ray Cassick \(Home\), Aug 19, 2006
    #4
  5. Sjouke Burry Guest

    Ray Cassick (Home) wrote:
    > "Rod Speed" <> wrote in message
    > news:...
    >
    >> wrote:
    >>
    >>
    >>>Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    >>>neighborhood. After calling the utility co. it was determined there
    >>>was too much demand on the grid. not anything specific in the house.
    >>>So here is my question can a low voltage situation kill a computer power
    >>>supply.

    >>
    >>A properly designed power supply should shut down in that situation.
    >>
    >>A badly designed power supply can be killed in that situation.
    >>

    >
    >
    > Just a bit curious as to how you think a power supply can be damaged by a
    > low voltage situation?
    >
    > Since all the regulation in a PS is designed to convert AC to DC and then
    > regulate those output voltages down to useable levels within a specified
    > tolerance I don't see how a low voltage could result in a dead PS. I DO see
    > how it can cause flakiness on the low voltage side since all outputs are
    > based upon a properly regulated input voltage tolerance, but all that should
    > result from a low input voltage is proportionally low output voltages.
    >
    > Personally I would think that most of the damage would have been caused by a
    > backlash of higher voltage that can often occur after low voltage
    > situations. This higher than normal voltage inrush could happen faster than
    > the regulators are prepared to handle and cause a very quick spike to get
    > through the filters and fry the lower voltage side of the regulation circuit
    > perhaps.
    >
    >
    >
    >

    A switching supply will draw a bigger current from the
    mains to compensate for less voltage, the output voltage
    wont drop ,power wont drop, so you need more current.
    When input is low enough ,and current becomes big enough,
    either the safety cuts in, or the supply blows.
    And that depends on the quality of the supply.
     
    Sjouke Burry, Aug 20, 2006
    #5
  6. Rod Speed Guest

    Ray Cassick (Home) <> wrote
    > Rod Speed <> wrote
    >> wrote


    >>> Hi, everybody. 2 weeks ago ther was a case of low voltage in the neighborhood. After
    >>> calling the utility co. it was determined there was too much demand on the grid. not
    >>> anything specific in the house. So here is my question can a low voltage situation
    >>> kill a computer power supply.


    >> A properly designed power supply should shut down in that situation.


    >> A badly designed power supply can be killed in that situation.


    > Just a bit curious as to how you think a power supply can be damaged by a low voltage
    > situation?


    Basically its unlikely that it was just a clean sag in the
    mains voltage, its likely that there was a considerable
    over voltage as well as the excess load was removed
    or disconnected itself in the case of high motor loads etc.

    The failure may be something as basic as
    the internal fuse thats on the mains active.

    > Since all the regulation in a PS is designed to convert AC to DC and then regulate those
    > output voltages down to useable levels within a specified tolerance I don't see how a
    > low voltage could result in a dead PS.


    See above.

    > I DO see how it can cause flakiness on the low voltage side


    That shouldnt happen, the ATX specs require that the supply
    shuts down cleanly when the output rails end up out of spec.

    > since all outputs are based upon a properly regulated input voltage tolerance, but all
    > that should result from a low input voltage is proportionally low output voltages.


    Nope, because the ATX spec requires that the supply must
    shut down cleanly when the output rails go out of spec.

    > Personally I would think that most of the damage would have been caused by a backlash of
    > higher voltage that can often occur after low voltage situations.


    Sure, thats what is likely what killed the badly designed
    supply. It couldnt handle that over voltage without dying.

    > This higher than normal voltage inrush


    Its unlikely to be that, much more likely to just be the higher
    voltage that killed it if it didnt just blow the internal fuse.

    > could happen faster than the regulators are prepared to handle


    There is no regulation to handle inrush current, it
    just goes thru the usual filter and gets absorbed
    by the main caps that are used to rectify the mains.

    > and cause a very quick spike to get through the filters and fry the lower voltage side
    > of the regulation circuit perhaps.


    That would normally fry the chopper etc. The output diodes
    are generally pretty brutal devices that arent easily killed by
    that sort of thing that would have to get thru the transformer.
     
    Rod Speed, Aug 20, 2006
    #6
  7. Rod Speed Guest

    Sjouke Burry <> wrote:
    > Ray Cassick (Home) wrote:
    >> "Rod Speed" <> wrote in message
    >> news:...
    >>
    >>> wrote:
    >>>
    >>>
    >>>> Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    >>>> neighborhood. After calling the utility co. it was determined there
    >>>> was too much demand on the grid. not anything specific in the
    >>>> house. So here is my question can a low voltage situation kill a computer
    >>>> power supply.
    >>>
    >>> A properly designed power supply should shut down in that situation.
    >>>
    >>> A badly designed power supply can be killed in that situation.
    >>>

    >>
    >>
    >> Just a bit curious as to how you think a power supply can be damaged
    >> by a low voltage situation?
    >>
    >> Since all the regulation in a PS is designed to convert AC to DC and
    >> then regulate those output voltages down to useable levels within a
    >> specified tolerance I don't see how a low voltage could result in a
    >> dead PS. I DO see how it can cause flakiness on the low voltage side
    >> since all outputs are based upon a properly regulated input voltage
    >> tolerance, but all that should result from a low input voltage is
    >> proportionally low output voltages. Personally I would think that most of the damage
    >> would have been
    >> caused by a backlash of higher voltage that can often occur after
    >> low voltage situations. This higher than normal voltage inrush could
    >> happen faster than the regulators are prepared to handle and cause a
    >> very quick spike to get through the filters and fry the lower
    >> voltage side of the regulation circuit perhaps.


    > A switching supply will draw a bigger current from the
    > mains to compensate for less voltage, the output voltage
    > wont drop ,power wont drop, so you need more current.
    > When input is low enough ,and current becomes big enough,
    > either the safety cuts in, or the supply blows.


    That increased current isnt what kills a badly designed supply.

    The only current that goes up is from the mains and the diodes
    that rectify the mains arent that marginal current capacity wise.

    What actually kills a poorly designed power supply in that
    situation is the inevitable associated mains surges as loads
    trip out due to the low mains voltage, particularly motor loads.

    > And that depends on the quality of the supply.
     
    Rod Speed, Aug 20, 2006
    #7
  8. John Doe Guest

    "" <> wrote:

    > Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    > neighborhood. After calling the utility co. it was determined
    > there was too much demand on the grid. not anything specific in
    > the house. So here is my question can a low voltage situation kill
    > a computer power supply. Taking in account it is not a cheap one:
    > I paid over $75.00US


    If you are concerned about poor house current, consider buying a
    voltage regulator (line conditioner). I've got a cheap one and it
    seems to do a good job. I don't need battery backup. I think a
    voltage regulator keeps things as stable as possible until it
    completely shuts down. That way your power supply doesn't see low
    voltages, it's all or nothing.

    Good luck.
     
    John Doe, Aug 20, 2006
    #8
  9. Rod Speed wrote:
    > Sjouke Burry <> wrote:
    >
    >>Ray Cassick (Home) wrote:
    >>
    >>>"Rod Speed" <> wrote in message
    >>>news:...
    >>>
    >>>
    >>>> wrote:
    >>>>
    >>>>
    >>>>
    >>>>>Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    >>>>>neighborhood. After calling the utility co. it was determined there
    >>>>>was too much demand on the grid. not anything specific in the
    >>>>>house. So here is my question can a low voltage situation kill a computer
    >>>>>power supply.
    >>>>
    >>>>A properly designed power supply should shut down in that situation.
    >>>>
    >>>>A badly designed power supply can be killed in that situation.
    >>>>
    >>>
    >>>
    >>>Just a bit curious as to how you think a power supply can be damaged
    >>>by a low voltage situation?
    >>>
    >>>Since all the regulation in a PS is designed to convert AC to DC and
    >>>then regulate those output voltages down to useable levels within a
    >>>specified tolerance I don't see how a low voltage could result in a
    >>>dead PS. I DO see how it can cause flakiness on the low voltage side
    >>>since all outputs are based upon a properly regulated input voltage
    >>>tolerance, but all that should result from a low input voltage is
    >>>proportionally low output voltages. Personally I would think that most of the damage
    >>>would have been
    >>>caused by a backlash of higher voltage that can often occur after
    >>>low voltage situations. This higher than normal voltage inrush could
    >>>happen faster than the regulators are prepared to handle and cause a
    >>>very quick spike to get through the filters and fry the lower
    >>>voltage side of the regulation circuit perhaps.

    >
    >
    >>A switching supply will draw a bigger current from the
    >>mains to compensate for less voltage, the output voltage
    >>wont drop ,power wont drop, so you need more current.
    >>When input is low enough ,and current becomes big enough,
    >>either the safety cuts in, or the supply blows.

    >
    >
    > That increased current isnt what kills a badly designed supply.


    Very well can.

    > The only current that goes up is from the mains and the diodes
    > that rectify the mains arent that marginal current capacity wise.


    The problem is the flyback regulator. Low voltage on the filter caps means
    an increased PWM duty cycle to compensate, stressing everything: drive
    transistors, flyback transformer, flyback diodes, etc.


    > What actually kills a poorly designed power supply in that
    > situation is the inevitable associated mains surges as loads
    > trip out due to the low mains voltage, particularly motor loads.


    Of course, that shouldn't make it past the input suppressors and filter caps.

    >
    >
    >>And that depends on the quality of the supply.

    >
    >
    >
     
    David Maynard, Aug 20, 2006
    #9
  10. Rod Speed Guest

    David Maynard <> wrote
    > Rod Speed wrote
    >> Sjouke Burry <> wrote
    >>> Ray Cassick (Home) wrote
    >>>> Rod Speed <> wrote
    >>>>> wrote


    >>>>>> Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    >>>>>> neighborhood. After calling the utility co. it was determined there was too much
    >>>>>> demand on the grid. not anything specific in the
    >>>>>> house. So here is my question can a low voltage situation kill a
    >>>>>> computer power supply.


    >>>>> A properly designed power supply should shut down in that situation.


    >>>>> A badly designed power supply can be killed in that situation.


    >>>> Just a bit curious as to how you think a power supply can be damaged by a low voltage
    >>>> situation?


    >>>> Since all the regulation in a PS is designed to convert AC to DC and then regulate
    >>>> those output voltages down to useable levels within a
    >>>> specified tolerance I don't see how a low voltage could result in a
    >>>> dead PS. I DO see how it can cause flakiness on the low voltage side since all
    >>>> outputs are based upon a properly regulated input voltage
    >>>> tolerance, but all that should result from a low input voltage is
    >>>> proportionally low output voltages. Personally I would think that
    >>>> most of the damage would have been
    >>>> caused by a backlash of higher voltage that can often occur after
    >>>> low voltage situations. This higher than normal voltage inrush
    >>>> could happen faster than the regulators are prepared to handle and cause a very quick
    >>>> spike to get through the filters and fry the lower voltage side of the regulation
    >>>> circuit perhaps.


    >>> A switching supply will draw a bigger current from the
    >>> mains to compensate for less voltage, the output voltage
    >>> wont drop ,power wont drop, so you need more current.
    >>> When input is low enough ,and current becomes big enough,
    >>> either the safety cuts in, or the supply blows.


    >> That increased current isnt what kills a badly designed supply.


    > Very well can.


    Nope, not when it didnt drop enough to cause the other system to turn a hair.

    >> The only current that goes up is from the mains and the diodes
    >> that rectify the mains arent that marginal current capacity wise.


    > The problem is the flyback regulator. Low voltage on the filter caps means an increased
    > PWM duty cycle to compensate,


    Yes.

    > stressing everything: drive transistors, flyback transformer, flyback diodes, etc.


    That shouldnt kill anything in a properly designed power supply.

    >> What actually kills a poorly designed power supply in that
    >> situation is the inevitable associated mains surges as loads
    >> trip out due to the low mains voltage, particularly motor loads.


    > Of course, that shouldn't make it past the input suppressors and filter caps.


    Shouldnt and didnt are too entirely separate matters.

    MUCH more likely than your scenario killing the power supply.

    >>> And that depends on the quality of the supply.
     
    Rod Speed, Aug 20, 2006
    #10
  11. Guest

    Ray Cassick (Home) wrote:

    > Just a bit curious as to how you think a power supply can be
    > damaged by a low voltage situation?
    >
    > Since all the regulation in a PS is designed to convert AC to
    > DC and then regulate those output voltages down to useable
    > levels within a specified tolerance I don't see how a low voltage
    > could result in a dead PS.


    Low AC voltage results in a higher duty cycle, which can cause
    inductor saturation. When an inductor saturates it stops
    opposing changes in current, and this can cause the current to
    increase beyond the capacities of the driving transistors.
     
    , Aug 20, 2006
    #11
  12. Thanks to all for the time and additional explanations.

    I never did get into all the intricacies of switching PS so it was all
    appreciated.

    <> wrote in message
    news:...
    >
    > Ray Cassick (Home) wrote:
    >
    >> Just a bit curious as to how you think a power supply can be
    >> damaged by a low voltage situation?
    >>
    >> Since all the regulation in a PS is designed to convert AC to
    >> DC and then regulate those output voltages down to useable
    >> levels within a specified tolerance I don't see how a low voltage
    >> could result in a dead PS.

    >
    > Low AC voltage results in a higher duty cycle, which can cause
    > inductor saturation. When an inductor saturates it stops
    > opposing changes in current, and this can cause the current to
    > increase beyond the capacities of the driving transistors.
    >
     
    Ray Cassick \(Home\), Aug 20, 2006
    #12
  13. Rod Speed wrote:
    > David Maynard <> wrote
    >
    >>Rod Speed wrote
    >>
    >>>Sjouke Burry <> wrote
    >>>
    >>>>Ray Cassick (Home) wrote
    >>>>
    >>>>>Rod Speed <> wrote
    >>>>>
    >>>>>> wrote

    >
    >
    >>>>>>>Hi, everybody. 2 weeks ago ther was a case of low voltage in the
    >>>>>>>neighborhood. After calling the utility co. it was determined there was too much
    >>>>>>>demand on the grid. not anything specific in the
    >>>>>>>house. So here is my question can a low voltage situation kill a
    >>>>>>>computer power supply.

    >
    >
    >>>>>>A properly designed power supply should shut down in that situation.

    >
    >
    >>>>>>A badly designed power supply can be killed in that situation.

    >
    >
    >>>>>Just a bit curious as to how you think a power supply can be damaged by a low voltage
    >>>>>situation?

    >
    >
    >>>>>Since all the regulation in a PS is designed to convert AC to DC and then regulate
    >>>>>those output voltages down to useable levels within a
    >>>>>specified tolerance I don't see how a low voltage could result in a
    >>>>>dead PS. I DO see how it can cause flakiness on the low voltage side since all
    >>>>>outputs are based upon a properly regulated input voltage
    >>>>>tolerance, but all that should result from a low input voltage is
    >>>>>proportionally low output voltages. Personally I would think that
    >>>>>most of the damage would have been
    >>>>>caused by a backlash of higher voltage that can often occur after
    >>>>>low voltage situations. This higher than normal voltage inrush
    >>>>>could happen faster than the regulators are prepared to handle and cause a very quick
    >>>>>spike to get through the filters and fry the lower voltage side of the regulation
    >>>>>circuit perhaps.

    >
    >
    >>>>A switching supply will draw a bigger current from the
    >>>>mains to compensate for less voltage, the output voltage
    >>>>wont drop ,power wont drop, so you need more current.
    >>>>When input is low enough ,and current becomes big enough,
    >>>>either the safety cuts in, or the supply blows.

    >
    >
    >>>That increased current isnt what kills a badly designed supply.

    >
    >
    >>Very well can.

    >
    >
    > Nope, not when it didnt drop enough to cause the other system to turn a hair.


    According to that kind of logic it didn't fail at all, yet it did.


    >>>The only current that goes up is from the mains and the diodes
    >>>that rectify the mains arent that marginal current capacity wise.

    >
    >
    >>The problem is the flyback regulator. Low voltage on the filter caps means an increased
    >>PWM duty cycle to compensate,

    >
    >
    > Yes.
    >
    >
    >>stressing everything: drive transistors, flyback transformer, flyback diodes, etc.

    >
    >
    > That shouldnt kill anything in a properly designed power supply.


    In theory nothing should... but it failed.


    >>>What actually kills a poorly designed power supply in that
    >>>situation is the inevitable associated mains surges as loads
    >>>trip out due to the low mains voltage, particularly motor loads.

    >
    >
    >>Of course, that shouldn't make it past the input suppressors and filter caps.

    >
    >
    > Shouldnt and didnt are too entirely separate matters.


    That's funny considering you've just been singing the "properly designed
    power supply" mantra.

    >
    > MUCH more likely than your scenario killing the power supply.


    Frankly, no. Surge suppression of the type you're arguing is relatively
    simple and fairly static from design to design. I.E. the power mains don't
    'change' when one goes from, say, a 400W design to a 450W. The flyback
    circuit, however, is a whole different situation. Get that off so the core
    goes into saturation with an unpredicted scenario and you've got fried
    flyback. And it's no very hard to do, especially when plagiarizing,
    'revising', or designing to power line 'specs' (meaning normal tolerances).


    >>>>And that depends on the quality of the supply.

    >
    >
    >
     
    David Maynard, Aug 21, 2006
    #13
  14. Rod Speed Guest

    David Maynard <> wrote
    > Rod Speed wrote
    >> David Maynard <> wrote
    >>> Rod Speed wrote
    >>>> Sjouke Burry <> wrote
    >>>>> Ray Cassick (Home) wrote
    >>>>>> Rod Speed <> wrote
    >>>>>>> wrote


    >>>>>>>> 2 weeks ago ther was a case of low voltage in the neighborhood. After calling the
    >>>>>>>> utility co. it was determined there was too much demand on the grid. not anything
    >>>>>>>> specific in the house. So here is my question can a low voltage situation kill a
    >>>>>>>> computer power supply.


    >>>>>>> A properly designed power supply should shut down in that situation.


    >>>>>>> A badly designed power supply can be killed in that situation.


    >>>>>> Just a bit curious as to how you think a power supply can be damaged by a low
    >>>>>> voltage situation?


    >>>>>> Since all the regulation in a PS is designed to convert AC to DC
    >>>>>> and then regulate those output voltages down to useable levels within a specified
    >>>>>> tolerance I don't see how a low voltage could result in a dead PS. I DO see how it
    >>>>>> can cause flakiness on the low voltage
    >>>>>> side since all outputs are based upon a properly regulated input voltage tolerance,
    >>>>>> but all that should result from a low input voltage is
    >>>>>> proportionally low output voltages. Personally I would think that
    >>>>>> most of the damage would have been
    >>>>>> caused by a backlash of higher voltage that can often occur after
    >>>>>> low voltage situations. This higher than normal voltage inrush
    >>>>>> could happen faster than the regulators are prepared to handle
    >>>>>> and cause a very quick spike to get through the filters and fry
    >>>>>> the lower voltage side of the regulation circuit perhaps.


    >>>>> A switching supply will draw a bigger current from the
    >>>>> mains to compensate for less voltage, the output voltage
    >>>>> wont drop ,power wont drop, so you need more current.
    >>>>> When input is low enough ,and current becomes big enough,
    >>>>> either the safety cuts in, or the supply blows.


    >>>> That increased current isnt what kills a badly designed supply.


    >>> Very well can.


    >> Nope, not when it didnt drop enough to cause the other system to turn a hair.


    > According to that kind of logic it didn't fail at all, yet it did.


    Wrong again. One PSU is properly designed and the other isnt.

    >>>> The only current that goes up is from the mains and the diodes
    >>>> that rectify the mains arent that marginal current capacity wise.


    >>> The problem is the flyback regulator. Low voltage on the filter
    >>> caps means an increased PWM duty cycle to compensate,


    >> Yes.


    >>> stressing everything: drive transistors, flyback transformer, flyback diodes, etc.


    >> That shouldnt kill anything in a properly designed power supply.


    > In theory nothing should... but it failed.


    Wrong again. One PSU is properly designed and the other isnt.

    >>>> What actually kills a poorly designed power supply in that
    >>>> situation is the inevitable associated mains surges as loads
    >>>> trip out due to the low mains voltage, particularly motor loads.


    >>> Of course, that shouldn't make it past the input suppressors and filter caps.


    >> Shouldnt and didnt are too entirely separate matters.


    > That's funny considering you've just been singing the "properly designed power supply"
    > mantra.


    Yes, clearly the one that did die isnt properly designed.

    >> MUCH more likely than your scenario killing the power supply.


    > Frankly, no.


    Fraid so.

    > Surge suppression of the type you're arguing is relatively simple and fairly static from
    > design to design. I.E. the power mains don't 'change' when one goes from, say, a 400W
    > design to a 450W.


    Yes, but you dont know that the badly designed power supply
    would have survived that surge even in the 400W version.

    Likely it never did the surge suppression properly.

    > The flyback circuit, however, is a whole different situation.
    > Get that off so the core goes into saturation with an unpredicted scenario and you've
    > got fried flyback.


    It is however trivial to design the supply so that that cant
    happen by monitoring the rectified mains voltage and shutting
    the supply down when its low enough to produce that result.

    > And it's no very hard to do, especially when plagiarizing, 'revising', or designing to
    > power line 'specs' (meaning normal tolerances).


    It is however trivial to design the supply so that that cant
    happen by monitoring the rectified mains voltage and shutting
    the supply down when its low enough to produce that result.

    Not a shred of rocket science required at all.
     
    Rod Speed, Aug 21, 2006
    #14
  15. Rod Speed wrote:
    > David Maynard <> wrote
    >
    >>Rod Speed wrote
    >>
    >>>David Maynard <> wrote
    >>>
    >>>>Rod Speed wrote
    >>>>
    >>>>>Sjouke Burry <> wrote
    >>>>>
    >>>>>>Ray Cassick (Home) wrote
    >>>>>>
    >>>>>>>Rod Speed <> wrote
    >>>>>>>
    >>>>>>>> wrote

    >
    >
    >>>>>>>>>2 weeks ago ther was a case of low voltage in the neighborhood. After calling the
    >>>>>>>>>utility co. it was determined there was too much demand on the grid. not anything
    >>>>>>>>>specific in the house. So here is my question can a low voltage situation kill a
    >>>>>>>>>computer power supply.

    >
    >
    >>>>>>>>A properly designed power supply should shut down in that situation.

    >
    >
    >>>>>>>>A badly designed power supply can be killed in that situation.

    >
    >
    >>>>>>>Just a bit curious as to how you think a power supply can be damaged by a low
    >>>>>>>voltage situation?

    >
    >
    >>>>>>>Since all the regulation in a PS is designed to convert AC to DC
    >>>>>>>and then regulate those output voltages down to useable levels within a specified
    >>>>>>>tolerance I don't see how a low voltage could result in a dead PS. I DO see how it
    >>>>>>>can cause flakiness on the low voltage
    >>>>>>>side since all outputs are based upon a properly regulated input voltage tolerance,
    >>>>>>>but all that should result from a low input voltage is
    >>>>>>>proportionally low output voltages. Personally I would think that
    >>>>>>>most of the damage would have been
    >>>>>>>caused by a backlash of higher voltage that can often occur after
    >>>>>>>low voltage situations. This higher than normal voltage inrush
    >>>>>>>could happen faster than the regulators are prepared to handle
    >>>>>>>and cause a very quick spike to get through the filters and fry
    >>>>>>>the lower voltage side of the regulation circuit perhaps.

    >
    >
    >>>>>>A switching supply will draw a bigger current from the
    >>>>>>mains to compensate for less voltage, the output voltage
    >>>>>>wont drop ,power wont drop, so you need more current.
    >>>>>>When input is low enough ,and current becomes big enough,
    >>>>>>either the safety cuts in, or the supply blows.

    >
    >
    >>>>>That increased current isnt what kills a badly designed supply.

    >
    >
    >>>>Very well can.

    >
    >
    >>>Nope, not when it didnt drop enough to cause the other system to turn a hair.

    >
    >
    >>According to that kind of logic it didn't fail at all, yet it did.

    >
    >
    > Wrong again.


    Yes, your statement was 'wrong' because, as you note below, one is not
    right so comparing to "the other system" says nothing about whether low
    voltage killed it.

    > One PSU is properly designed and the other isnt.
    >
    >
    >>>>>The only current that goes up is from the mains and the diodes
    >>>>>that rectify the mains arent that marginal current capacity wise.

    >
    >
    >>>>The problem is the flyback regulator. Low voltage on the filter
    >>>>caps means an increased PWM duty cycle to compensate,

    >
    >
    >>>Yes.

    >
    >
    >>>>stressing everything: drive transistors, flyback transformer, flyback diodes, etc.

    >
    >
    >>>That shouldnt kill anything in a properly designed power supply.

    >
    >
    >>In theory nothing should... but it failed.

    >
    >
    > Wrong again.


    Do you ever *think* about what's said or do you just invent whatever seems
    convenient?

    The statement was perfectly true. In THEORY, nothing should fail in a
    properly designed power supply.

    > One PSU is properly designed and the other isnt.


    Which is what I've said all along.

    >>>>>What actually kills a poorly designed power supply in that
    >>>>>situation is the inevitable associated mains surges as loads
    >>>>>trip out due to the low mains voltage, particularly motor loads.

    >
    >
    >>>>Of course, that shouldn't make it past the input suppressors and filter caps.

    >
    >
    >>>Shouldnt and didnt are too entirely separate matters.

    >
    >
    >>That's funny considering you've just been singing the "properly designed power supply"
    >>mantra.

    >
    >
    > Yes, clearly the one that did die isnt properly designed.


    Glad we agree on something so now you can stop singing "in a properly
    designed power supply."

    >>>MUCH more likely than your scenario killing the power supply.

    >
    >
    >>Frankly, no.

    >
    >
    > Fraid so.


    'Fraid not.


    >>Surge suppression of the type you're arguing is relatively simple and fairly static from
    >>design to design. I.E. the power mains don't 'change' when one goes from, say, a 400W
    >>design to a 450W.

    >
    >
    > Yes, but you dont know that the badly designed power supply
    > would have survived that surge even in the 400W version.


    True, I don't. But surge suppression is trivial and relatively constant
    from design to design while flyback design isn't so the likelihood of
    screwing up one or the other or both is not the same.

    > Likely it never did the surge suppression properly.


    You mean "likely" because you're in the middle of an argument and saying
    "likely" seems a good thing to say.

    >>The flyback circuit, however, is a whole different situation.
    >>Get that off so the core goes into saturation with an unpredicted scenario and you've
    >>got fried flyback.

    >
    >
    > It is however trivial to design the supply so that that cant
    > happen by monitoring the rectified mains voltage and shutting
    > the supply down when its low enough to produce that result.


    That costs money. But, no, it isn't 'trivial' because it takes knowing at
    what line voltage core saturation would occur (as but one consideration).


    >>And it's no very hard to do, especially when plagiarizing, 'revising', or designing to
    >>power line 'specs' (meaning normal tolerances).

    >
    >
    > It is however trivial to design the supply so that that cant
    > happen by monitoring the rectified mains voltage and shutting
    > the supply down when its low enough to produce that result.


    That costs money. But, no, it isn't 'trivial' because it takes knowing at
    what line voltage core saturation would occur (as but one consideration).


    > Not a shred of rocket science required at all.


    An opinion that proves you've never designed one.

    And with that I am finished with this thread. You can not post how it's all
    trivial and pretend you 'won' something.
     
    David Maynard, Aug 23, 2006
    #15
  16. Rod Speed Guest

    David Maynard <> wrote
    > Rod Speed wrote
    >> David Maynard <> wrote
    >>> Rod Speed wrote
    >>>> David Maynard <> wrote
    >>>>> Rod Speed wrote
    >>>>>> Sjouke Burry <> wrote
    >>>>>>> Ray Cassick (Home) wrote
    >>>>>>>> Rod Speed <> wrote
    >>>>>>>>> wrote


    >>>>>>>>>> 2 weeks ago ther was a case of low voltage in the
    >>>>>>>>>> neighborhood. After calling the utility co. it was
    >>>>>>>>>> determined there was too much demand on the grid. not
    >>>>>>>>>> anything specific in the house. So here is my question can a
    >>>>>>>>>> low voltage situation kill a computer power supply.


    >>>>>>>>> A properly designed power supply should shut down in that situation.


    >>>>>>>>> A badly designed power supply can be killed in that situation.


    >>>>>>>> Just a bit curious as to how you think a power supply can be
    >>>>>>>> damaged by a low voltage situation?


    >>>>>>>> Since all the regulation in a PS is designed to convert AC to
    >>>>>>>> DC and then regulate those output voltages down to useable levels
    >>>>>>>> within a specified tolerance I don't see how a low voltage
    >>>>>>>> could result in a dead PS. I DO see how it can cause flakiness
    >>>>>>>> on the low voltage side since all outputs are based upon a properly regulated
    >>>>>>>> input voltage tolerance, but all that should result from a low
    >>>>>>>> input voltage is proportionally low output voltages. Personally I would think
    >>>>>>>> that most of the damage would have been
    >>>>>>>> caused by a backlash of higher voltage that can often occur
    >>>>>>>> after low voltage situations. This higher than normal voltage inrush
    >>>>>>>> could happen faster than the regulators are prepared to handle
    >>>>>>>> and cause a very quick spike to get through the filters and fry
    >>>>>>>> the lower voltage side of the regulation circuit perhaps.


    >>>>>>> A switching supply will draw a bigger current from the
    >>>>>>> mains to compensate for less voltage, the output voltage
    >>>>>>> wont drop ,power wont drop, so you need more current.
    >>>>>>> When input is low enough ,and current becomes big enough,
    >>>>>>> either the safety cuts in, or the supply blows.


    >>>>>> That increased current isnt what kills a badly designed supply.


    >>>>> Very well can.


    >>>> Nope, not when it didnt drop enough to cause the other system to turn a hair.


    >>> According to that kind of logic it didn't fail at all, yet it did.


    >> Wrong again.


    > Yes, your statement was 'wrong'


    Pathetic, really.

    > because, as you note below, one is not right so comparing to "the other system" says
    > nothing about whether low voltage killed it.


    I never said that the low voltage is what killed it.

    >> One PSU is properly designed and the other isnt.


    >>>>>> The only current that goes up is from the mains and the diodes
    >>>>>> that rectify the mains arent that marginal current capacity wise.


    >>>>> The problem is the flyback regulator. Low voltage on the filter
    >>>>> caps means an increased PWM duty cycle to compensate,


    >>>> Yes.


    >>>>> stressing everything: drive transistors, flyback transformer,
    >>>>> flyback diodes, etc.


    >>>> That shouldnt kill anything in a properly designed power supply.


    >>> In theory nothing should... but it failed.


    >> Wrong again.


    > Do you ever *think* about what's said or do you just invent whatever seems convenient?


    Have you ever actually managed to bullshit your way out of a wet paper bag ?

    > The statement was perfectly true.


    Nope.

    > In THEORY, nothing should fail in a properly designed power supply.


    Irrelevant to what killed that particular power supply.

    >> One PSU is properly designed and the other isnt.


    > Which is what I've said all along.


    Liar. You claimed a particular failure mechanism without any
    evidence that that is what actually killed that particular supply.

    >>>>>> What actually kills a poorly designed power supply in that
    >>>>>> situation is the inevitable associated mains surges as loads
    >>>>>> trip out due to the low mains voltage, particularly motor loads.


    >>>>> Of course, that shouldn't make it past the input suppressors and filter caps.


    >>>> Shouldnt and didnt are too entirely separate matters.


    >>> That's funny considering you've just been singing the "properly designed power supply"
    >>> mantra.


    >> Yes, clearly the one that did die isnt properly designed.


    > Glad we agree on something so now you can stop singing "in a properly designed power
    > supply."


    Or I could tell you to go and **** yourself instead.

    >>>> MUCH more likely than your scenario killing the power supply.


    >>> Frankly, no.


    >> Fraid so.


    > 'Fraid not.


    Fraid so.

    >>> Surge suppression of the type you're arguing is relatively simple
    >>> and fairly static from design to design. I.E. the power mains don't
    >>> 'change' when one goes from, say, a 400W design to a 450W.


    >> Yes, but you dont know that the badly designed power supply
    >> would have survived that surge even in the 400W version.


    > True, I don't. But surge suppression is trivial and relatively constant from design to
    > design


    Irrelevant when you dont know that the supply
    that failed has adequate surge suppression.

    And it aint just what is trivial that matters, there are plenty of examples
    where stupid cost cutting sees inadequate surge suppression.

    > while flyback design isn't so the likelihood of screwing up one or the other or both is
    > not the same.


    You dont know that the design was screwed up and that it
    wasnt just cost cutting that produced the inadequate design.

    >> Likely it never did the surge suppression properly.


    > You mean "likely" because you're in the middle of an argument and saying "likely" seems
    > a good thing to say.


    Wrong, as always. I said that because even with the lower powered
    versions of PSUs, anyone with a clue has noticed that some do have
    inadequate surge suppression and other gross design deficiencys
    like killing what is power from the PSU when the PSU fails.

    >>> The flyback circuit, however, is a whole different situation.
    >>> Get that off so the core goes into saturation with an unpredicted scenario and you've
    >>> got fried flyback.


    >> It is however trivial to design the supply so that that cant
    >> happen by monitoring the rectified mains voltage and shutting
    >> the supply down when its low enough to produce that result.


    > That costs money.


    So does surge suppression.

    > But, no, it isn't 'trivial' because it takes knowing at what line voltage core
    > saturation would occur (as but one consideration).


    Even the most basic testing of the design would show that problem.

    So it is indeed trivial to have the supply shut down when the
    input voltage has dropped below what the design can handle.

    >>> And it's no very hard to do, especially when plagiarizing, 'revising', or designing to
    >>> power line 'specs' (meaning normal tolerances).


    >> It is however trivial to design the supply so that that cant
    >> happen by monitoring the rectified mains voltage and shutting
    >> the supply down when its low enough to produce that result.


    > That costs money.


    So does surge suppression.

    > But, no, it isn't 'trivial' because it takes knowing at what line voltage core
    > saturation would occur (as but one consideration).


    Even the most basic testing of the design would show that problem.

    So it is indeed trivial to have the supply shut down when the
    input voltage has dropped below what the design can handle.


    >> Not a shred of rocket science required at all.


    > An opinion that proves you've never designed one.


    Wrong, as always. Its a fact that there isnt a shred of rocket
    science required at all to have the supply shut down when the
    input voltage is below what the design can handle.

    > And with that I am finished with this thread.


    You have always been, and always will be, completely and utterly irrelevant.

    > You can not post how it's all trivial and pretend you 'won' something.


    Only silly little children give a flying red **** about 'winning', child.
     
    Rod Speed, Aug 23, 2006
    #16
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