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Re: Power Supply Tester

 
 
Paul
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      09-21-2009
James D. Andrews wrote:
> I should have asked here for recommendations before ordering, but I finally
> got around to ordering a cheap PSU tester last night. I'm interested in
> your experiences with these.
>
> The model I ordered was a Rexus PST-3 Power Supply Tester with LCD for $21.
> I read all of the 170+ reviews, and all were 4-5 stars except for less than
> a handful of bad experiences (a couple obviously from not following the
> directions). The biggest complaint was about the skimpy, foreign-tongue
> manual.
>
> I can't afford the $800 supermodel that tests everything all at once and
> makes coffee, so I had to go with an affordable model that like most
> products I'm sure will break down over many years of use. The old you get
> what you pay for thing here, but it was priced comparitively to others and
> it was not the cheapest model.
>
> So, do you think I'm going to regret this? Are these devices as useful as
> they say? Anyone have any major problems with this or other PSU testers?
> Anything I need to be particularly concerned about with using one of these?
>


Well, consider what you're getting for the money.

The packaging prevents the built-in load from consuming too much power.
Some power supplies, have minimum current consumption values printed
on the label. (In some cases, the minimum current values are only listed
in the PSU spec sheet, so they may try to hide the minimum load needed.)
Generally, the minimum load requirement, results in the voltages being
in spec. The voltages may drift up out of spec, if sufficient load is not
there.

One reviewer on Newegg, notes that a disk drive caught fire, while using
the device. It isn't clear, exactly what was wired up at the time, but
it could be: Power supply, tester, hard drive. If the tester didn't place
sufficient load, perhaps one of the +12V rails rose higher than normal.

A poster in the past, did some research on his hard drive, and discovered
there is a transient suppressor on the +12V (and probably +5V rail as well).
The purpose of the suppressor, is to snub any inductive spikes resulting
from turning off the supply while the hard drive is still drawing
current. The transient suppressor is intended to stop spikes, like stop
a +15V spike on the +12V rail.

If the power supply sustains an overvoltage, like puts out +15V on the
+12V rail for long periods of time, the transient suppressor on the
hard drive controller board, roasts and burns up. I think that is what the
reviewer on the Newegg reviews saw, was the transient suppressor filling
the room with smoke.

So, what can we learn from that.

Test power supply with tester, and leave other equipment disconnected.
If the supply has a minimum load, and it is not met, only the little
tester has to face the consequences.

Other than that, what you're getting, is a $20 multimeter, with the
ability to switch to multiple input voltage channels and take readings.
You're probably also getting one or two power resistors, which draw
a minimum load from the supply. The device is too small to be drawing
a proper load (i.e. a minimum load sufficient for any power supply
you might happen to find). There are some stinko supplies from
past years, where the minimum load is really high, and for those,
I probably wouldn't use the tester. (I could use the tester, but
seeing +15V reading wouldn't tell me whether the supply was bad
or not. It would be telling me, I need to meet the minimum load.)

I built my own load box, and it cost me more than your $20 item.
With mine, when I pick the resistors, I can aim for a 100W load,
and place an 80mm fan next to the resistors. Mine lacks voltage
readings, and I do that with a separate multimeter on volts range.

None of these tests is particularly useful. You might feel happier,
to test the power supply, at more than one loading. Say 100W and
300W load. check the voltages. Or, do a cross-regulation test,
by loading one rail heavily, and noting what happens to the
percentage deviation on the other rails. That will give you
some idea, whether the supply is actually in spec. Step load tests,
tell you whether the voltages will remain stable, when a quick
change in the loading occurs (like the instant you start a 3D
game).

A single point measurement, tells you whether the supply behaves
with that exact loading. The Rexus would be testing a "really
light load", while mine tests a "light load". Doing a Tomshardware
and testing a "heavy load", to the point of causing the power supply
to smoke, is kinda pointless as well. If you're to use any load, the
load should represent the load expected on the real system. If
you're running a couple GTX285, then your load tester should
be further up the power scale.

So, I don't see it as money wasted, as long as you don't freak
out when you see the readings. A high reading, could be from
insufficient load, or it could be because of a failure. I would
not use "real" devices as a load, as in the disk drive case,
the drive could burn if the voltage is still high.

With the supplies that I own, and have tested, I've never had
a problem with minimum load. I'm sure many home users will
never see a problem either. But I still have to give a
warning, because there are crappy supplies out there.

Paul
 
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