power supply

  • Thread starter Thread starter Not so quick
  • Start date Start date
MrB said:
Mr w-tom,

You were not there. 220 volts was measured on the line with a digital
voltmeter. Believe what you want, it happened. My main point was that most
of the computers survived with minor or no damage, even though the surge
protectors blew out. It was good protection for the price.
MrB
Click to expand...
I can believe the voltage. See my reply to w_tom. A surge protector is
designed to protect from very short spikes, not sustained high voltage.
They usually "blow" after carrying enough current to cause them to destruct,
allowing them to become an open circuit. Since they are placed across the
incoming line, the line voltage will remain the same after their destruction.

Many surge protectors contain their own over current protection. The MOVs
could well draw enough current to trip this device before they themselves
were destroyed. This would protect the attached loads, and could well leave
the line circuit breaker untripped. In this case, with the load being removed,
the line voltage would be close to 220 V, even with a small load on the other
side of the circuit, since the voltmeter draws very little current.

The ground wire has nothing to do with what happens with an open neutral.
It's only purpose is for safety. It is connected to the neutral(s) only
at the service entry point. If the neutral becomes open, the return path
for the circuit is through the load on the other side of the 120/240 V
circuit to the other "hot" wire, with 240 V between the two "hot" wires.

Virg Wall
--

Any sufficiently advanced technology
is indistinguishable from magic.

Arthur C. Clarke's Third Law
 
w_tom said:
A sag is a brownout. All computers must work just fine even
when 120 VAC drops (sags) to 90 VAC. This was a defacto
standard 30 years ago and is required in Intel ATX specs.
That means AC voltage drops so low that incandescent lamps are
at maybe 35% intensity. How often does your voltage drop that
low?

Yes, not all power supplies meet those specs. We see them
often because too many in N America only purchase using one
spec - price. Power supplies must contain many functions.
How to sell a power supply at higher profit? Forget to add
those functions and sell it for maybe $40. Too many computer
experts don't even understand basic electrical concepts which
is why too many clone computer users have strange problems.
Posted above are numbers found in the numerical specs provides
by acceptable power supplies. Information that minimally
acceptable power supplies provide because they actually meet
those specs.

Then we have people who fix things without first learning
why the problem exists. Their solutions include 500 watt
power supplies (Home Improvement's "More Power" solution) and
plug-in UPSes. Expensive solutions because the original
supply was not purchased based upon technical requirements.
All computers must work just fine - even startup with the
maximum load of peripherals - when 120 VAC line is only 90
VAC. That 90 VAC is called a sag or brownout.

If power is lost for more than 15 milliseconds, then a
computer can shutdown. This can result in data loss on FAT
filesystem disks. Just another reason we want NTFS
filesystems on our hard drives - or need a UPS for data
protection.
Click to expand...

I was using 'incorrectly'. Is there a name for a power interruption
that lasts > 15 milliseconds but not long enough to be considered
an outage? I would say like .5 seconds. Thanks : -) This has
been a very instructional thread to me.
 
The 'greater than 15 millisecond' power loss would be a
blackout. All power supplies have internal electricity (300+
volts) stored in capacitors. All properly constructed
supplies must exceed 15 milliseconds of power loss (blackout)
so that, for example, the UPS can switch a relay from AC mains
to UPS battery. Relays take 10+ milliseconds to respond.

If a power supply is much larger than its load, then power
supply may take longer to discharge those input capacitors.
The spec is for full load:
Hold up time, full load: 16ms. typical
Click to expand...

What is power off or shutdown? When power is removed,
those capacitors discharge, and power supply goes into
brownout; then blackout. IOW some will claim that brownouts
can damage hardware. If true, then power off (shutdown) will
also damage hardware.

Power supply will either supply full voltage to the
important DC voltage outputs - or shutdown. In fact, the
signal wire called Power Good is the supply telling
motherboard that all voltages are OK. Either all DC voltages
remain in spec - or power supply cuts off all voltages and
removes the Power Good signal.

We would routinely test electronic designs to see how low
voltage would really go. Typically, power supplies would work
just fine down to 85 VAC; then shutdown. One even reported a
Sony TV that worked just fine down to 65 VAC. Everything must
exceed specs to meet specs. So, 80 VAC to that Sony TV would
really not be a brownout or blackout - from TV's perspective.
What happens if power is lost for more than 16 milliseconds
and power supply keeps working? What could have been a
blackout was not - from perspective of a lightly loaded
computer power supply. And so there is a fuzzy line between
blackout and brownout. What must be asked is from which
perspective - utility's or power supply's?

80 VAC would be a brownout so low as to be a violation of
utility specifications. During heavy load usage, utility
cannot let 120 VAC drop (brownout) more than 5%. Even 3%
voltage drop is considered a major event. If they cannot
maintain above 5% brownout, then utility must shed load (cut
off power).

Just some background material as to what power supplies do
and what they may confront.
 
Those in warmer climates suffer because they don't have some
of nature's fabulous testing equipment. Snow around earth
ground rod being good safety device. When a neutral fails,
then earth ground rod and other wires (such as CATV wire) take
up current from a missing neutral. Snow then melts faster at
the rod which is also why voltage would not climb to 220
volts.

In one case, because earth ground was missing, then phones
in other neighborhood homes rang continuously. Electricity
used the CATV wire and phone wires to complete a circuit
created by a failed neutral and home's missing earth ground.
Utility emergency response used fire department infrared
vision to find the offending house and locate a red hot CATV
wire inside walls. Just another example of why earth ground
is important for human safety - to pick up currents normally
carried by a neutral wire. Again, - attention lurkers - if
snow (or frost) is melting first around earth ground rod, then
homeowner should verify integrity of his neutral wire.

Earth ground rod (if properly installed) is but another
reason why 220 volts would not appear on that 120 volt main.
220 volts on a 120 volt circuit means house had much more
problems than just a failed neutral.

Increased voltage (that is much less than 220 volts) due to
a failed neutral could be why incandescent light bulbs burn
out every month - prematurely. They do have light bulbs even
where 'snow don't go'.
 
Surge protectors do not remove load (disconnect computer)
from AC mains upon failure. That indicator light simply says
a surge protector's components (MOVs) are disconnected from AC
mains while appliance still remains connected to AC main.
What kind of protection was that? Surge protector
disconnected in millisecond while computer continued to
confront excessive line voltage for many minutes? That means
the surge protector never protected computer. Computer
protected itself.

UL1449 2nd Edition is why surge protector components must
disconnect - so that they don't start a fire - as mid 1980
surge protectors once did. Typically, only tiny thermal fuse
to MOVs blow. Now the surge protector is equivalent to a
power strip. Power strip surge protector never protected
those computers. Protector simply did as UL1449 demands -
disconnected the surge protector components so as to not
create fire. It is a tiny thermal fuse that blows so that
surge protector does not burn. That is what the silly
indicator light says. The tiny thermal fuse disconnected
surge protector components from AC main.

How pathetically informative is that indicator light? MOVs
are removed from a more expensive protector - and that light
still says everything is OK!
http://www.zerosurge.com/HTML/movs.html
 
w_tom said:
Surge protectors do not remove load (disconnect computer)
from AC mains upon failure.
Click to expand...

Many "surge protectors" are in the form of a power strip as you
mention below. These often have over-current protection in the form
of a circuit breaker, which upon overload, will isolate the strip
from the line. Before failing, the MOV(s) may well draw enough
current to trip that breaker. The computer is then isolated from
the malfunctioning line.

That indicator light simply says
a surge protector's components (MOVs) are disconnected from AC
mains while appliance still remains connected to AC main.
What kind of protection was that? Surge protector
disconnected in millisecond while computer continued to
confront excessive line voltage for many minutes? That means
the surge protector never protected computer. Computer
protected itself.
Click to expand...

Nobody has mentioned an indicator light before. More FUD!
UL1449 2nd Edition is why surge protector components must
disconnect - so that they don't start a fire - as mid 1980
surge protectors once did. Typically, only tiny thermal fuse
to MOVs blow. Now the surge protector is equivalent to a
power strip. Power strip surge protector never protected
those computers. Protector simply did as UL1449 demands -
disconnected the surge protector components so as to not
create fire. It is a tiny thermal fuse that blows so that
surge protector does not burn. That is what the silly
indicator light says. The tiny thermal fuse disconnected
surge protector components from AC main.
Click to expand...

Many "surge protectors" do not have indicator lamps. They must
demonstrate that the MOVs fail in an open circuit mode before
reaching an excessive temperature.
How pathetically informative is that indicator light? MOVs
are removed from a more expensive protector - and that light
still says everything is OK!
http://www.zerosurge.com/HTML/movs.html
Click to expand...

This company, (Zero Surge), makes surge protectors that do not use
MOVs. Obviously they do like those that do! More FUD!
You need to learn how circuits are wired. An open neutral can put two
120 V outlets in series on a 240 V supply. The ground wire has nothing
to do with the outlets power. It is not even connected to the neutral
except at a single point at the power entrance. It remains connected only
to the case, and does not normally carry any current.

Some MOV surge protectors do have MOVs between the "hot" wire and ground.
The conductance of this MOV before it failed could contribute to the
abnormal current which opened the protective breaker. In this sense,
the "surge protector" did indeed protect the computer!

Virg Wall, P.E. CA E5107
--

Any sufficiently advanced technology
is indistinguishable from magic.

Arthur C. Clarke's Third Law
 
Most surge protectors had no circuit breaker to meet
UL1449. MOVs are disconnected by internal thermal fuse; not
by a circuit breaker. Failing MOVs could never trip a 15 amp
circuit breaker and meet UL1449 - not cause a fire. 15 amp
circuit breaker has nothing to do with UL1449, indicator lamp
(the only indication that surge protector circuits are
'fried'), or surge protector circuits.

Unlike power strip surge protectors, a conventional power
strip contains a 15 amp circuit breaker for human safety; so
that a 15 amp wall receptacle is not overloaded. How to make
a surge protector? Remove the 'essential for human safety' 15
amp breaker from a $3 retail power strip. Add some $0.10
components. Sell the assembly as a surge protector for $15 or
$25. What a markup and they still eliminated the 15 amp
breaker - that is not part of a surge protection circuit.

That 15 amp circuit breaker has nothing to do with the surge
protector circuit. UL1449 requires that a protector not
burn. A failing surge protector circuit could not trip a 15
amp breaker AND not burn. The indicator light to indicate
fried surge protector says nothing about the 15 amp breaker.
Indicator light says a tiny (minimal amperage) thermal fuse to
MOVs has burned out.

None of this protects a computer from 220 volts on a 120
volt line.

Failing MOV could never shunt enough current for long enough
to trip that 15 amp circuit breaker. This made obvious in MOV
data sheets.
 
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