Velocity Reviews - Re: power supply questions

Fredd Wright wrote:
> I have a Gateway GT5014 media center PC with a Pentium D 2.80 GHZ and 4GB of
> RAM (although XP only recognizes 3.25GB) I also have 2 SATA hard drives and
> an external USB hard drive. About 2 months ago, i installed a Radeon HD
> 4350 video card so i could run a second monitor. Since then, occasionally,
> my computer shuts down unexpectedly (maybe 3 or 4 times in the past 2
> months). Yesterday, my computer shut down and wouldn't boot up - not even
> with the Sytem Restore CD. I tried everything and as a last resort, yanked
> out 2 of the memory chips. It booted so i replaced the memory.
>
> Today, the computer shut down again without warning. At this point, i'm
> thinking it's the power supply. I'm running the OEM 300W power supply. My
> guess is either it's bad or too low for my current setup.
>
> Questions are:
>
> 1. How much do i need in PS wattage (i'm just looking for an estimate as i
> realize it's hard to tell these kinds of things)? Would too much be bad?
> If i got a 600w and the PC didnt' need it, would it matter or could i end up
> damaging something.
> 2. With a higher watttage power supply, would there be any cooling issues
> or would that already be covered with a good quality psu?
> 3. Any brand/type recommendations?
>
> I'm sort of a newbie so please forgive me if these are silly questions.
>
> Fredd
>
>

An HD 4350 would use less power than a HD 4550, and you can see here,
that number is pretty low. It's hard to believe the new video card
is "tipping over" the supply.

http://www.xbitlabs.com/images/video...4550_power.png

While the computer is running, I'd try Speedfan and try to get a reading
of CPU temperature, if that is available from the hardware monitor. It
could be that the CPU is overheating (heatsink clogged with dust or fan
not spinning etc). The CPU has THERMTRIP, and if the CPU overheats,
the logic signal from the processor, turns off the power supply.

http://www.almico.com/speedfan443.exe (a utility to display temp and voltage)

*******

It could also be, that the power supply is old and weak, and no longer
able to provide the rated power on the label of the supply. A higher
rating is OK.

If you look on the label, it'll say something like "5V @ 20A". What
that means, is the motherboard can draw any level of current flow
between zero amperes DC and 20 amperes DC, and the power supply
can deliver that. The power rating is an "up to" value. So if
you installed a 630W supply and the internal components of the
computer need 150W, the power supply produces exactly 150W. The
power supply can produce any value between zero watts and "up to" 630 watts.

Virtually every number on the label of the power supply, has a meaning.
You can select another supply, either by matching or exceeding the
maximum ratings on the label, or you can do a calculation of the
power consumed by the components and develop rating numbers that
way.

http://www.recycledgoods.com/product...87427_zoom.jpg

12Va @ 18A 12Vb @ 18A
5V @ 25A -12V @ 0.8A
3.3V @ 25A +5VSB @ 2A

+5V & +3.3V up to 180 watts max
all main rails up to 288W max
+12Va & +12Vb up to 22 amps max combined

Now, that label tells you some things about the 12V supply. It is
split in two pieces. One piece powers the processor. The other
piece powers the rest of the 12V loads in the computer. The total
may look like 36 amps, but it isn't. The supply has an upper combined
limit of 22 amps. That means, you could load 12Va to 18A, 12Vb to 4A,
and that would be the limit. Or load 12Va to 4A, 12Vb to 18A and again
be at the limit. Such a rating, gives flexibility in terms of whether
12Va or 12Vb is the one which is heavily loaded.

The whole supply works that way - each individual DC output has a high
rating, in case it is the one supplying most of the power. But the
overall ratings for the whole supply are low. (In the following,
power in watts equals volts times amps.)

To give another example "+5V & +3.3V up to 180 watts max".
I could load it to 5V @ 25A plus 3.3V @ 16.6A or
I could load it to 5V @ 19.5A plus 3.3V @ 25A
but I can't take both rails to the max at the same time.

You can shop for a new supply, by matching those ratings.

Now, one problem I have with those ratings, is the 25A rating on
3.3V and 5V. More modern supplies tend to give 20A on those rails,
and you end up buying a much larger capacity supply, to try to get
25A as a rating. For example, I found this one.

http://www.newegg.com/Product/Produc...82E16817151096

Now, that's too expensive a solution, and this is just intended to
provide another label to look at.

The advertising copy, lacks details, so we have to use a picture of
the label. I had to use an image editor program, and adjust brightness
and contrast in this picture, to be able to read it!

http://images17.newegg.com/is/image/newegg/17-151-096-Z05?$S640W$

3.3V @ 24A \___ 130W max, which is less than the other example
5V @ 24A /
12V1 @ 24A \___ 576W max, 576/12=48A, so more than double the other supply
12V2 @ 24A /
-12V @ 0.8A \___ same ballpark
+5VSB @ 2.5A /

That would be close on ratings. I hope the lower rails, really aren't
drawing 130W.

Modern supplies put their "effort" into 12Va and 12Vb (12V1 and 12V2).
Older supplies had more solid 3.3V and 5V, with the 12V being more of
an afterthought. And that means, buying and matching ratings can be
a frustrating experience.

I have a couple dandy Enermax supplies I bought on sale within the last
couple of years, but they don't make those models any more. Mine are
rated at 3.3V @ 30A and 5V @ 30A and 160W combined, which is pretty good.
I expect I could use one of those as a substitute for your old supply
without worrying. I suspect the 130W combined is enough to do the job
too.

On my old P4 based system, the measured load (using a clamp-on DC ammeter)
at the motherboard was:

3.3V @ 14.4A, 5V @ 0.55A, 12V @ 5.6A

and from that, the combined load on lower rails is around 50W. So
having a combined lower rails rating of 180W is kinda overkill in
that example. Even a combined of 130W would have been enough.
There is a tiny bit more 5V used by storage devices, but not enough
to change the picture drastically. The technology on your motherboard
would be similar enough, for me to estimate your lower rails would
be around 50W combined for 3.3V/5V rails to run the motherboard.
Maybe 70W total for the whole computer, on lower rails.

So something like this, with lower rails 24A and combined 130W is
likely to be good enough. And overall wattage high enough to run
your PC. I'd be more concerned, if the combined 3.3V/5V power rating
dropped below 100W.

http://www.newegg.com/Product/Produc...82E16817371035

I picked this one last example, as an extreme. What is special about
this supply, is it is more efficient (kicks out less waste heat)
than any other supply. But look at the lower rails. It has a
20A rating (which would still meet my 14.4A load), but the combined
is only 100W for 3.3V/5V. Again, this would probably work with
your motherboard, but would not be my first choice. More run of the
mill and less expensive supplies, would offer more loading margin
on the lower rails. The less efficient supplies would come with
the 130W lower rail rating.

http://images17.newegg.com/is/image/newegg/17-121-080-Z12?$S640W$

And lastly, one of my favorite pictures of an ATX supply,
demonstrating how *not* to market a supply :-) One of the products
this company makes, is rated for 500W, yet won't run a computer
with a P4 processor in it. And that's why a proper label with
combined ratings information is important, to make sure it really
is the right supply. That particularly bad supply, couldn't even
deliver 15A on 12V to run a P4. So you can't just go out and
buy a "500W" supply and hope for the best. In some cases, the
supply is so poorly designed, it won't run half the computers
out there that are really only drawing 150-200W. Using the
overall wattage rating in selecting a supply, is not enough.
Looking at the other numbers, shows how well balanced and matched
to the computer the supply is.

http://images10.newegg.com/NeweggIma...163-018-06.JPG

Paul