Can Low Voltage kill a power supply?

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?

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 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.

"Rod Speed" wrote in message
...
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) wrote:
"Rod Speed" wrote in message
...

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.

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.

Sjouke Burry wrote:
Ray Cassick (Home) wrote:
"Rod Speed" wrote in message
...

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.

" 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.

Rod Speed wrote:
Sjouke Burry wrote:

Ray Cassick (Home) wrote:

"Rod Speed" wrote in message
...


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 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.