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- Quick estimate of power required?
January 9, 2008, 2:40 pm
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Is there a web site showing how to quickly estimate power supply wattage
I want to build a quad core Q6600 based PC overclocked to about 3GHz, with 3
x 500G or larger sata hard drives, some P35 based motherboard, and a cheap
2D video card (for video editing). Approximately how large a power supply do
Re: Quick estimate of power required?
Make sure it is a good quality PSU and not just powerful according to
it's specs. I always use PC Power and Cooling power supplies because they
actually rate them honestly where many companies rate their PSUs on their
"startup" power and not the actual "running" power. IOW, a PSU rated at 500w
may only run that at startup and only run at 350w or so. I would guess that
a 400-450w PSU should take care of your needs without any problems. If you
go with a more powerful video card you may have to up that to 500w to be on
the safe side, but if you go with a good manufacturer you should be fine at
400-450w. The PC Power and Cooling "Silencer" series is virtually
that......silent. I am running an Silencer 800w in this liquid cooled system
and the very quiet water pump can be heard over the PSU. I run 4x 500g hdds,
2x 8800GTX video cards, 3x 120mm fans, 2x DVDRW drives and a Q6600 @
3.25Ghz. 3Ghz should be easily attained with stock cooling and probably at
stock VCore if you get lucky. My Q6600 seems to hit a wall at about 3.4Ghz
because of the high VCore it takes to get there. My E6600 would easily reach
3.5Ghz without a problem on water cooling. I built a system for my son with
that processor and it easily reached 3.2Ghz on stock cooling. Performance of
the two are close except on benchmarks like 3DMark06 where the quad core
handily outperforms the C2D by over 4000 points on this SLI system (13000 vs
17000+). You will probably find that the Q6600 will idle a bit higher than
you expect. Mine idles at close to 40c with liquid cooling but never goes
above 55c under stress. The E6600 would idle in the upper 20sC and run about
the same as the Q6600 stressed. Both are well below max.
Re: Quick estimate of power required?
Processor - 95W for Q6600 G0 stepping
- power scales as F*C*V**2, meaning directly proportional to
frequency F (25% higher for your overclock), plus more voltage
may also be applied to Vcore. The power factor there is
divided by V_squared_nominal. Based on someone else's overclock
settings, I got about 146W for the Q6600 at full load. (And
it only reaches full load under certain conditions. Gaming
is not one of them.) If you didn't need any extra Vcore to
hit 3GHz, then the power would be only 95W * 1.25, so each
overclocker needs slightly different power.
- Vcore converter circuit is about 90% efficient. This is purely
a guess. So scale the result by 1/0.90. 146/0.90 = 162W at
the ATX12V input connector. 162W / 12V = 13.5 amps from 12V2.
Motherboard plus RAM - estimate 50W here. Majority of power is for
Northbridge. RAM power is negligible. Only a few
watts per stick. 50W is a ballpark number to cover it.
Motherboard comes from 3.3V or 5V rail, and we don't
know which might be used. It could even use 12V to
run Vdimm, for example. No way to know.
Hard drives - 12V @ 0.6A and 5V @ 1A. Call it 12W a piece.
CD/DVD - varies, but use 12V @ 1.5A and 5V @ 1.5A, with the 12V only
drawn when the motor spins. The CD in my current computer is
measured at 1 amp at full motor speed. DVD burners will use more
power, but again, you need media in place to draw motor current
Fans - estimate 12V @ 0.5A for three of them. Check the label for exact numbers.
Standby current - 5V @ 2A perhaps, from +5VSB
Video - 30W for low end. 130 or 165W for high end (from Nvidia or ATI).
Total so far = 162 + 50 + 36 + 25.5 + 6 + 10 + 30 = 319.5W
In selecting a supply, you'll end up with a dual rail 12V1/12V2 supply.
12V1 powers peripherals on their 12V rail. 12V2 powers the processor. The
gauging of the 12V2 will determine the supply size you end up with.
This is the smallest supply I might use for the job. Min acceptable current
on 3.3V and 5V of 20 amps each. (Combined power of at least 100W for
3.3V/5V outputs.) That is enough to ensure the motherboard gets enough,
because we don't know the exact current split. 12V2 @ 17A is just enough
to handle the processor (I like 3 amps margin). The 12V1, if I totaled the
numbers right, is about 3.8A and does not tax the 17A capacity of the 12V1
output. So we ended up with a 430W supply. I'd probably go a bit bigger than
this in practice. An "80+" style supply, while expensive, also reduces the heat
dumped into the room by the power supply itself.
SeaSonic S12 II SS-430GB ATX12V / EPS12V 430W Power Supply $108
+3.3V @ 20A, +5V @ 20A, +12V1 @ 17A, +12V2 @ 17A, -12V @ 0.8A, +5VSB @ 2.5A
The advantage of supplies with 24 pin connectors, where all the 12V is
tied to one output, is you don't have to worry about how the current
is split between 12V1 and 12V2. The manufacturers of supplies are
not honest about their internal workings, and it is possible that
one with four equally rated outputs, is actually using a single
source rail internally (plus four current limiters of some sort).
By stating the ratings this way, it removes the need to figure out
the split between 12V1 and 12V2, and select a supply big enough
to meet 12V2 processor rail.
CORSAIR CMPSU-550VX ATX12V V2.2 550W $99
+3.3V @ 30A, +5V @ 20A, +12V @ 41A, -12V @ 0.8A, +5VSB @ 3A
The above is not an endorsement of those two supplies. They're meant
to illustrate possible solutions. Read the reviews for each item, to
see if there are a lot of DOAs, early failures, spectacular failures,
and so on.
In the power supply industry, there is a lot of subcontracting. For
example, Seasonic might make quite a few of the "80+" designs you see
for sale. Seasonic make their own. Companies like Antec, Corsair,
Ultra, would buy their supplies from someone else. There are review
sites which discuss the source of various supplies.
For a list of brands to avoid, check out the "Tier 5" section of this
page. Again, this page is not kept up to date, so new and undesirable
branding will be added by the industry every day.
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