Doc said:
I have a PC Power and Cooling 470W unit that's a few years old but
hasn't had a lot of mileage on it and the rig it was in didn't come
near to stressing its limits. It was modestly pricey when I got it so
I figure it's worth seeing if it's still working the way it's supposed
to. If I want to ensure it's not doing anything that might fry a h/d -
voltage spikes perhaps...or? - is there a way to test it, or someplace
you trust to send it for testing?
Thanks.
There are all sorts of test facilities out there, but the price
they'll charge, you could easily buy half a dozen to a dozen supplies,
just for talking to them.
*******
At the power supply factory, they use various flavors of "Chroma Tester".
The tester might be able to do things, like dynamic tests, such as
a load step, and observe the results. Chroma is the brand name.
Other (cheaper) brands likely exist.
When you see such things advertised, they're shown mounted in a
rack mount form factor. A thing like this would sit next to the
test station perhaps. With computer programming, a simple "pass/fail"
can be shown on a screen somewhere, so staff can sort the good from
bad supplies. The boxes would be cabled together, and a computer
would remotely program them with the various tests to run.
http://img.directindustry.com/image...-equipment-for-power-supply-30085-2703793.jpg
There are tests of things that "don't matter" to end users. One
test is the "hi pot" test, which checks for isolation between
the line and the DC outputs. It's that isolation that
prevents you from getting a shock. And it's tested to perhaps
1100 volts or so. I don't know if a Chroma tester does that, or
some other setup is used. It requires applying a potential across the
thing, to test whether it can withstand the high voltage. While that
test can just be applied to the transformer, it's also helpful
to know there are no violations on the finished assembly (PCB)
either.
*******
For a home tester, the cheapest test to do, is to build a "load box".
That puts a steady DC load, and does not create any transient conditions.
I made my own, using power resistors from my "good" electronics store.
A switch connects between PS_ON# and COM, to control the supply when
it sits on the bench. I also power a 12V fan from the supply (80mm)
and it blows over the power resistors, to remove some of the heat.
If a power supply was weak, and you connected a "representative load",
such as 200W worth of resistors, then you get some idea whether it could
power a "real" computer.
So the ingredients, include a 20 pin or 24 pin shell similar to the
motherboard connector. A bag of crimp pins, for wiring things up.
In my case, I soldered crimp pins to the power resistors, and just
plug them into the main connector. My load box does not present
a heavy load. It's not even "representative".
For each rail, you have to decide on what load to use.
Perhaps it would be 5 amps from 3.3V, 5 amps from 5V, and 10 amps from 12V.
That would be a total of 162W say. You then do the math, to figure out
what resistors to use. 3.3V/5A = 0.66 ohms. I was at the electronics
store today actually, and bought a package of 0.33 ohm resistors for $2.00.
By placing two of those resistors in series, and putting them across 3.3V and COM,
I have my load for that rail. On the 5V rail, it would be 5V/5A = 1 ohm,
and there are 1.0 ohm resistors at the store too. Actually, the stock
at my store is pretty thin, and there's only about one package of
resistors on each hook. So if I needed a whole bunch of the same
value of resistor, I'm screwed.
Those resistors are rated at 10W. I know that 3.3V*5A is 16.5 watts,
which is more than the 10W resistor is rated for. But, my plan called
for two resistors in series, the resistors have equal values, and without
any additional math, I see 8.25 watts being dissipated in each one. The
resistors will get boiling hot, and some level of moving air over them
is recommended. (The resistors have a ceramic body.) This is one reason
I didn't built a purely representative load box, because I didn't want
to have to build a good cooling solution for it. In a way, a good sized
load box, is like a "hair dryer", in terms of the heating.
In school, the favored apparatus, was a panel full of 120V light bulbs.
I've never seen the thing used, but the device was pointed to as being
a load that was used for experiments. And preferred, because of the
cheapness of light bulbs. The problem with a light bulb, is the "cold"
resistance is a lot lower than the "hot" resistance, and for any electronic
supplies, they "tip over" when the light bulb is connected. To illustrate
that, I tried connecting a 12V automotive bulb, a marker light, to a 12V @ 2A
wall wart, and the "cold" load would trip the overcurrent on the supply. So
even though the bulb draws well less than 2 amps when running, the cold
resistance draws enough current, that the overcurrent stops it immediately.
The power resistors I buy at the store, are a bit better than that, and
are rated for 5% initial tolerance, plus some degree of temperature coefficient.
The only resistance that has next to no temperature related effect is
manganin wire, and its resistance is pretty close to a constant. But
many other materials have a significant effect from cold to hot.
You can build yourself a load box, then measure the voltage with
a multimeter, but it's not much of a test. I use my load box for
testing brand new supplies. I leave them running for a couple
hours, just to weed out any supplies that "explode immediately"
when you use them. After the couple hours are up, I again measure
the voltages with the multimeter, and then conclude the supply
is safe to use with my new motherboard.
I have one supply here, with an extremely weak 12V output. Drawing
more than 0.1 amp, flattens the 12V output. My load box could be
used to evaluate such an ancient supply, and conclude it was broken.
So if your supply is weak, the load box does have a use. But for
more subtle problems, the load box is useless. A multimeter can't
see "glitches" very well. And more expensive instruments are
needed to do anything fancy.
*******
Back when hard drive controller boards, had the component side
facing outwards, you could see two transient suppressor parts, near
where the DC comes into the PCB. One on the 5V rail, one on
the 12V rail. If you were to rip the Molex out of the drive
while the drive was spinning, a small inductive arc might appear
at the power terminals. The transient suppressor, is intended to
"clip" the transient. So perhaps the 12V rail begins to clip,
when a voltage of 15V or more appears there.
Those two protection devices will burn, if a power supply overvolts.
The reason is, the transient protection devices are only intended to
handle short, high energy events. A long slow burn, will fry them.
And a power supply that has gone nuts, and put 8V on 5V or 15V on 12V,
will burn those parts. I only found out about this, when a poster
did the leg work, and traced down the part numbers, and from
that, we figured out what it was there for. At those voltages,
there's a good chance something on the controller board got
fried too. Once burned, those things would no longer
be protecting anything.
Since current controller boards, have the components facing inwards,
it's no longer possible to visually inspect for burned transient
suppressors, or burned motor controller chips. If the drive is
dead, you can always take the thing apart, to satisfy your curiosity.
Paul
