3 blown Power supply's in 6 months.

  • Thread starter Thread starter RobW
  • Start date Start date
As an industrial electrical designer (large industrial ovens and furnaces) I
always design and fuse for the protection of the device.
 
Tom

A fuse does NOT exist purely to save human life.. the fuses inside a hi-fi
power amplifier or CB or computer power supply are there to protect
circuits.. some will be fast blow, some will be slow blow, and some are
thermal types..

Note also that automotive fuses do NOT exist to save human life.. and if you
had followed any links on the URL given to you, that would have become
patently clear to you too..


--
Mike Hall
MVP - Windows Shell/User
 
As an industrial electrical designer (large industrial ovens and furnaces) I
always design and fuse for the protection of the device.
Click to expand...

As a designer that's worked in the industrial sector for almost 2
decades, I also spec fuses/breakers for the protection of the wiring and
device depending on the application. I don't recall ever fusing for
protection of personnel.

All the breakers in my SD panel in my home are sized based on the wire
gauge and not the devices connected to wiring. All of the fuses in the
non-switching PSU's I've used and or build were sized to protect the PSU
itself (components).

Wonder what else he's going to try and tell us this time.
 
w_tom said:
First thing that power supply must provide is a long
list of written and numeric specs.
Click to expand...

This is still a user beware situation. Many PSU makers actually lie
about what load their product will support. They may rate the PSU as a
400W unit but include the voltages and their supposed load support when
those voltages aren't used, or they list an aggregate load for a common
rail voltage when the combined or simultaneously load will be much
smaller. That 400W cheapie PSU may only be able to actually support a
concurrent 200W to 300W load. Figure 50% to 75% of actual wattage
rating from a cheapie PSU. So you may simply be trying to suck out 300W
of an actual load from a PSU that can only supply 200W but has a "400W"
sticker on it. A good PSU will tell you what is the load available per
tap but also mention if there are any caveats regarding a combined load
limit across taps.

Just because it says 400W on its sticker doesn't mean it will actually
support that load level on all its taps at the same time. Not only is
that a concern but also many cheapie PSU makers will outright lie about
what load can be safely applied to any tap. There is also the problem
of excessive ripple. Although many computer components are designed to
accommodate some ripple, they won't handle it when it is so severe as to
look like a sawtooth pattern on an oscilloscope. It sounds like the OP
has been trying to get by on cheap PSUs and then wondering why they
blow. Sort of like buying the cheapest tires and expecting them to be
equivalent to the pricey ones. Your PSU provides the lifeblood of your
computer.
 
J-Dee said:
im from UK and every power cable has to have a fuse in UK so suppose
it
depends where your from. if you use fuses it could well be a problem.
Click to expand...


If that is true then the fuse needs to be the slow-blow type. The
sudden burst of amps surging through a normal fuse could easily blow it
when the computer is powered on. The slow-blow fuse will prevent it
from opening for a short one-time surge. However, if the fuse in the
power cord blew then the OP would be asking why he has to keep replacing
power cords or the fuses in them. He is saying that he is replacing
PSUs. Even if he replaced the PSU, it wouldn't work until he replaced
the power cord fuse, so he would've still mentioned having to replace
fuses. Doesn't sound like it is a fuse problem.
 
RobW said:
I pulled the case and found a fuse that now resembles a used
firecracker which I guess came out of the PSU. (the PSU has a bottom
intake fan with large gaps).
I am going to take Leythos's suggestion and investigate which fuse on
the PSU is blown. I may have to get someone who knows what they are
looking at to examine it, :-).
I am in Australia and the mains is 240VAC.
The power leads have no fuses.
Thanks again and I will post the outcome for anyone who is interested.
Click to expand...


That fuse usually means you are drawing too many amps from the PSU. You
are overheating and overloading the PSU. See my other post regarding
the use of cheapie power supplies and why you cannot simply rely on the
stickered wattage rating. It also shows that you are using cheapie
PSUs. The better ones use a reset circuit that will reset after awhile
(when the heat dissipates). A fuse is cheaper.
 
Hell. There were times in my past career when I would not even fuse a 10HP
440/460V motor. I would rather have it burn up than have a fuse blow at an
inopportune time. Example: an emergency ventilator in an explosive
atmosphere. When the LFL (lower flammability limit) reached 7.5% that motor
came on and ran until the environment was again safe or the motor destroyed
itself because of "whatever"!

--
Regards,

Richard Urban

aka Crusty (-: Old B@stard :-)

If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!
 
Leythos said:
Most computer PSU's use CAPS on the DC side and they don't have more
than 20+ VDC on most of them, the caps will also discharge in a short
amount of time due to the way a PSU is designed.
Click to expand...


It is not so much of getting a small shock, if any. It is usually more
the case of causing physical damage to yourself due to the involuntary
quick withdraw of your hand. Getting a shock often doesn't do much harm
when working on electronics, but you've spent 5 minutes winding your
fingers, hand, and arm in amongst all the cords and components, some of
which have barbs or sharp edges. When you get shocked, you withdraw in
a straight line and drag your skin across all those jaggies. The shock
didn't hurt you. You hurt your because of your reaction the the shock.
The bzzzt or buzz might not hurt, but your hand or arm might look like
you had a fight with a feral cat.

I'd give the PSU about 10 minutes to discharge, and that is WITH the
power cord connected to the computer and to the outlet. If the OP is
sucking out an excessive amount of current, there is also a good chance
that some parts are hot inside.
 
If that is true then the fuse needs to be the slow-blow type. The
sudden burst of amps surging through a normal fuse could easily blow it
when the computer is powered on. The slow-blow fuse will prevent it
from opening for a short one-time surge. However, if the fuse in the
power cord blew then the OP would be asking why he has to keep replacing
power cords or the fuses in them. He is saying that he is replacing
PSUs. Even if he replaced the PSU, it wouldn't work until he replaced
the power cord fuse, so he would've still mentioned having to replace
fuses. Doesn't sound like it is a fuse problem.
Click to expand...

Actually the OP stated, later, that he found a fuse blown inside the PSU
once he opened it.
 
Hell. There were times in my past career when I would not even fuse a 10HP
440/460V motor. I would rather have it burn up than have a fuse blow at an
inopportune time. Example: an emergency ventilator in an explosive
atmosphere. When the LFL (lower flammability limit) reached 7.5% that motor
came on and ran until the environment was again safe or the motor destroyed
itself because of "whatever"!
Click to expand...

That's not right, if the motor is drawing too much current, there is a
reason, and continued running will generate excessive heat, which is
worse on a vent for an explosive environment. Heck, even the heaters
could kick-out a motor before the fuses did in some cases - where the
fuses were sized wrong.
 
An old horse story!

I was doing T.V. repair in the 60's. There was a new high rise in Fort Lee,
NJ. One of our technicians was up on the 9th floor working on a woman's
console T.V. (friggin HUGE). He was squatting down behind the set - the
power was off. He accidentally touched the 2nd anode on the CRT. His legs
convulsed and sprung him backward, through the open sliding balcony doors
and over the rail to his death!

He was my friend.

--
Regards,

Richard Urban

aka Crusty (-: Old B@stard :-)

If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!
 
I would have wanted to have the motor draw too much current, and run for
another minute. That could be the difference between a massive explosion and
loss of human life OR the opportunity for the plant personnel to vacate!

--
Regards,

Richard Urban

aka Crusty (-: Old B@stard :-)

If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!
 
An old horse story!

I was doing T.V. repair in the 60's. There was a new high rise in Fort Lee,
NJ. One of our technicians was up on the 9th floor working on a woman's
console T.V. (friggin HUGE). He was squatting down behind the set - the
power was off. He accidentally touched the 2nd anode on the CRT. His legs
convulsed and sprung him backward, through the open sliding balcony doors
and over the rail to his death!

He was my friend.
Click to expand...

That's terrible, worst incident of appliance shocking I've ever read.
Sorry for your loss.

When I worked on 14kv lines, I remove all metal from my person, at least
as much as possible.

We had a couple incidents where people were racking in switch-gear and
crossed the stabs and made a real big mess, but I wasn't around then. We
even had a contractor vacuuming a 14kv unit after they had drilled holes
in the panels/sides - the dust arced against the bus bars... He had
copper colored safety glasses and burns on his arms/face.

I've also seen contractors cut conduits that were suppose to be safed,
only to have the 440 still be hot.

One time, when I was new to all of this, I was following an old timer on
a motor replacement on an automated system - it was only about 5HP, but
he had turned the machine to STOP (not power off) and told me to just go
ahead and wire the pecker-head. Being young, stupid, and new, I grabbed
the three lines, they brushed up against the stair frame and made one
heck of a bang. I never followed anyone again without making the system
safe (electrical/mechanical) again.
 
I would have wanted to have the motor draw too much current, and run for
another minute. That could be the difference between a massive explosion and
loss of human life OR the opportunity for the plant personnel to vacate!
Click to expand...

I would have been afraid that the load could be caused by a shaft
bearing or some other physical condition that could lead to
sparks/excessive heat.

We used double exhaust systems in our grain systems, same in the cement
systems, in case one purge system didn't work.
 
When I was in Electronic school, courtesy of the Navy, we were in our 3
phase section of training. We each had out own work module and fuse box.
After coming back from coffee break one day a young fella a few seats down
picks up the three phase leads and says "I wonder if these are hot?". He
then touched two of the phases together. He woke up 3 days later in
intensive care.

--
Regards,

Richard Urban

aka Crusty (-: Old B@stard :-)

If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!
 
When I was in Electronic school, courtesy of the Navy, we were in our 3
phase section of training. We each had out own work module and fuse box.
After coming back from coffee break one day a young fella a few seats down
picks up the three phase leads and says "I wonder if these are hot?". He
then touched two of the phases together. He woke up 3 days later in
intensive care.
Click to expand...

I was in AT (Avation Electronics Technician) training in Memphis around
84, I saw things like that once in a while during my 3 months there :)
 
We designed in double and triple redundancy, but the final safety stage ran
till the last outcome - whatever that may have been!

Man, I would have hated to have to tell 20 widows and widowers that their
loved ones were dead because a $3.00 fuse blew and the exhauster went single
phase at 1/3 speed!

--
Regards,

Richard Urban

aka Crusty (-: Old B@stard :-)

If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!
 
He's out checking his books now (-:

--
Regards,

Richard Urban

aka Crusty (-: Old B@stard :-)

If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!
 
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