Power Supple Question - How Much Power Needed?

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I am running an Asus P5K MB with an Intel Quad CPU, an Asus GE Force
8600 GT
graphics card, 1 DVD Drive, and with 8GB of RAM. I was running 2
hard disks
before and just added a 3rd one into the system. According to
things I have
read, I should be running a 600 Watt PSU with this kind of
hardware. Presently I
have an Enermax 450 Watt PSU in there and
according to all the voltage meters on
the Asus PC Probe Program that
came with the MB, I am not getting into any
danger zones on voltage. So
I am wondering if I really need to spend another $75
to upgrade my power
supply or if I can continue using the one I have? I rather
not spend the
money if it is not needed and is there any other way to find out
if I am
really exceeding the limitations of the current PSU in terms of power

Many thanks…

Re: Power Supple Question - How Much Power Needed?

On Thu, 29 Jan 2009 00:54:44 -0600, marcbkk

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Unless you are overclocking a lot, your system should
consume under 225W.  A 600W PSU could be unnecessary
overkill based on my next paragraph...

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These days it's not so much wattage but current on the 12V
rail that matters.  Depending on how old your 450W PSU is,
it could have more, or less 12V current capacity than the
average 450W PSU have.

PC Probe can be a good first indicator but not reliable for
accurate PSU voltage measurement due to inaccuracies
inherant in mobo onboard measurement techniques on most
motherboards.  Use of a multimeter probing for voltage at
the power connector to the load (CPU 12V connector and 20 or
24 pin mainboard connector) is a far more accurate
indication if the PSU is staying within it's capability,
within ATX specs under varying load conditions.

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Do some stress tests like Prime95's Torture test for an
hour, and memtest86+ overnight, 3DMark 2003 (or 2005 at the
newest considering the video card bottleneck for gaming).
If these run stabily, there is no indication you need to
replace the PSU based on your current system load (keeping
in mind what I've written above).

If you were to replace the video card with one quite a bit
more power hungry, and of course will be using it for
gaming, then the potential to exceed the long-term
capability of an average 450W name-brand PSU would be

Re: Power Supple Question - How Much Power Needed?

marcbkk wrote:
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There are online power calculators where you detail your system and it
calculates your minimum power requirement.  Plugging what you've
described above into one of those yields a number less than 300W, but
you should try it youself to make sure your system is completely
specified.  Also, as power supplies age, they get less able to deliver
their rated power, so buying large (and buying quality) is always advised.

Shooting from the hip, your 450W is probably enough, as long as it's of
a reasonable quality.  (I don't have any experience with Enermax.)

Re: Power Supple Question - How Much Power Needed?

marcbkk wrote:
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Here is my estimate

P5K MB, 8BG RAM - I allocate 50W for chipset and RAM. The rail it loads
                   cannot be determine without considerable work. Power
                   may come from a lower voltage rail, for example.
Core2 Quad - 95W, scale by Vcore efficiency 95W/0.90 = 105.6W from the 12V rail
8600GT 43W (mostly from 12V)
DVD drive - 5V @ 1.5A 12V @ 1.5A, or whatever is printed on the label.
             Blueray may involve larger values. Some CD types, less.
             So 25W when media is present, as an estimate.
Hard drive - 5V @ 1A 12V @ 0.6A, with modern drives now doing better
              than that. Say 12W per drive, times three, gives 36W.
Standby - assorted loads running from +5VSB, 10W

Total - 50+105.6+43+25+36+10=269.6W

And my estimates tend to be on the high side. The
estimate is in the same ballpark as Kony's.

There are a range of Intel Quad processors, and in my above choice of
95W, I've made an assumption about your budget and what you'd
likely have bought. There are some quads which draw 136W for
example, but they're expensive and not many people buy them.
Intel has just introduced a series of lower power quads, but
they're priced as if they're cherry picked (unlikely - Intel
has the ability to tune their product somewhat, and the parts
might not be any harder to make than the others). I doubt
there will be many takers, with the pricing structure. But
someone in Intel marketing thinks so.


Re: Power Supple Question - How Much Power Needed?

Cheers kony. I am only using my system for usual computing, no gaming
and no
overclocking and I see no need to ever upgrade the graphics card
for what I do.
The main purpose for all that RAM in the first place was
because I am a digital
photographer and work on some large files at
times. So I basically need a lot of
RAM and some big hard drives for
large file storage. At the moment I have a 1TB
and the other one large
one is 1.5TB. The 3rd drive is just a boot drive with
only 160GB on it I

I do realize though that a PSU will degrade over time
and eventually
not pump out what it should be pumping anymore in terms of
wattage. I
guess with voltage levels those can become irregular as well. I think
Enermax is about 2 years old, maybe less, but I think they guarantee
products. Unlike the cheapo Chinese ones I used to buy in the past
before I
learned there was a real difference in PSU quality when I had a
PC that wouldn't
boot because the power supply was worn out. This
happened to me a couple times
before I eventually switched to something
reliable, or course 5 times the price
as well.

I probably wont bother with a multimeter measurement at this point and
the stress test stuff is a bit over my head, but what you said so far
gives me good peace of mind.

Thanks Grinder, I had once used an online
calculator on the newegg.com
web site and that is how I came up with that figure
of 550-600 Watts
being required. I guess that really would be overkill based
upon what
kony is saying.

Enermax, here in Thailand anyway, seems to be
regarded as the best
quality PSU that is available. I am sure there are other
good brands out
there as well, but Enermax seems to be highly rated and
considered at
least at a reliable standard.

Re: Power Supple Question - How Much Power Needed?

Cheers Paul. Thank you for such a good, detailed analysis and so good to
that I am really adequately powered at the moment. I have not had
any problems
since adding that 3rd hard drive, but didn't want to start
having any either.

The CPU I bought is actually the Intel Q6600. It was about US$200
back in around March of last year. I am not sure who much
power this one draws,
but if you tell me how I could check that then I
could let you know.

What had sent off the alarms for me in the first place was the fact
that a
calculations I did on the newegg.com web site said that with my
CPU, graphics
card, 8GB of RAM, DVD Rom Drive, and 3 hard drives that I
would need 533 Watts.
I realize that these calculators are just a rough
guide, but it would have had
me over powering my system by 50%!

Re: Power Supple Question - How Much Power Needed?

On Sat, 31 Jan 2009 20:51:46 -0600, marcbkk

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Buying a PSU rated for 500 to 600W for that system (if you
didn't have a PSU already) would be a reasonable thing to do
since PSU are often starting in the midrange quality level
at that wattage, whereas in the past, when PSU had more
current on the 5V rail, it translated into as much current
but 1A x 5V = 5W, 1A x 12V = 12W, so naturally for any
particular quality level, today's PSU would be rated higher
total wattage than years ago.

In other words, although I estimated under 225W, I would not
recommend buying a 250W PSU even if it had particularly high
12V current ratings, unless it were a industrial rated PSU
where they don't market based on peak current.  In general a
high quality 350W PSU, or median quality 400W or higher
would be the best match for that system, or higher wattage
rated if there were a reasonably near future plan to upgrade
to higher powered parts.

Re: Power Supple Question - How Much Power Needed?

Thanks for the additional technical info Kony. I think the conclusion is
that I
have more than enough power for my current system with the 450W
PSU and no need
to worry about increasing PSU capacity. I also have no
short or long term plans
to upgrade anything further so I should be
fine. It is good to know I am not
going to have any power problems and
so far, since putting in the new added hard
drive a few weeks ago, there
have been no problems at all. Cheers...

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