The Power Consumption

[bandieramonte]

I make this thread to understand more the subject of power consumption of a PC's components, and to help me the right decision when buying a PSU.

I already have all my components, except for the PSU.... My relevant specs are:
- Q6600 (and will overclock to 3.4 Ghz)
- Two MSI 8800 GTS G92 SLI (factory overclocked to 730 Mhz Core clock)
- 4 GB RAM memory PC 6400 CAS4
- Cooler Master GeminiII for CPU cooling
- 7 case fans
- 1 HD, 1 DVD burner

I'm trying to decide to buy between the Thermaltake ToughPower 750 Watts, or the Thermaltake Toughpower 1200 Watts. The later costs roughly 27% more. The goal of this thread is to determine if it's necessary to pay more for the 1200 Watts. (I ONLY have these two choices because those are the only ones that I have available to buy here).

This is my reasoning here:

power_consumption.jpg (42.02 KiB) Viewed 7646 times

The Q6600 at load, and without overclocking takes up to 197 Watts.

power_consumption1.jpg (65.53 KiB) Viewed 7646 times

A single 8800 GTS 512 G92 @ 678 Mhz Core Clock, at full load consumes a whole up to 255 Watts. So SLI would consume 255 x 2 = 510 Watts only on GPU's.

Now, this is without adding up the additional wattage if overclocking the Q6600 to 3.4 Ghz, and the additional wattage one would have to incur if using two MSI 8800 GTS G92's which are factory overclocked to 730 Mhz, which is 52 Mhz Core Clock more than the one in the analysis. So even more PSU power is needed.

So, till now, only with a stock Q6600 and two 8800 GTS G92's @ 678 Mhz core clock, we got: 197 + 510 = 707 Watts. This is without not even including the minor power needed for the HD, DVD, fans, CPU cooler, RAM, etc etc....

We know that PSU's don't provide 100% power. The ToughPower, for instance, has roughly 85% max efficiency. So, for a 750 Watts power, we got 750 x 0.85 = 637.5 Watts of real power. This is well below of what only a stock Q6600 and two 8800 GTS G92's would need. So, I would not imagine what PSU would be needed to completely power at full load the complete system, including overclocking..... Maybe the toughpower 1200 Watts would do?

So, I need people to please correct me if I'm wrong, since your replies will help me decide if it's necessary to pay the extra cash for the toughpower 1200 Watts.

Thanks a lot.

[KnightRid]

I vote for the 1200w. If you already are close to 750 with what you added up, you HAVE to have extra incase you decide to upgrade video cards/cpus, etc.

Your video cards should only be pulling those watts when you are actually pushing them to the limit, so your normal power usage will be a LOT less than those high figures, but for gaming when you are using everything at max, you will need the power.

Spend the money

Mike

[bubba]

check out the PSU calculator http://extreme.outervision.com/PSUEngine went through and filled in some stuff and never got over 600w, a quality 750w should be fine.

[hnzw_rui]

Huh? Color me confused but wasn't the power consumption in LR's review the system (total) power consumption and not just the processor's? In fact, isn't the power consumption in both reviews already the total?

If that's the case, then you probably won't need more than 750W.

[Apoptosis]

You'll need a beefy system to need 1200+ watts... Even with the Skulltrail system it's hard to break 600W and that's with 8 cores and SLI'd video cards... I can through a pair of 8800 GTS 512's back on skulltrail and tell you what it get... that's two 45nm quad-cores at 3.2GHz and FB-DIMM's that are power hungry

I'll tell you right now that this

- Q6600 (and will overclock to 3.4 Ghz)
- Two MSI 8800 GTS G92 SLI (factory overclocked to 730 Mhz Core clock)
- 4 GB RAM memory PC 6400 CAS4
- Cooler Master GeminiII for CPU cooling
- 7 case fans
- 1 HD, 1 DVD burner

shouldn't be breaking 750W...

[bandieramonte]

OK I'm learning a lot about this power consumption stuff. I did many tries on the impressive calculator that bubba just sent me. I had some interesting results. If I put 100% peak load, 15% aging, 100% TDP (which would be the worse case scenario, I don't know if a quad reaches 100% TDP), and the totality of my components, the program says that I need the recommended PSU wattage of 618 Watts. But the calculator has one missing thing; I can't overclock the video cards there!

So, If I buy a 750W PSU, having 85% efficiency, I guess I would really have 637 Watts, of real power, which is really close to that minimum 618 watts. What worries me is that if the calculator had the overclocking on video cards functionality, then maybe it could have breached beyond the 637 watts level, meaning that I would need something better than the Thermaltake ToughPower 750 Watts... Am I wrong?

Huh? Color me confused but wasn't the power consumption in LR's review the system (total) power consumption and not just the processor's? In fact, isn't the power consumption in both reviews already the total?

If that's the case, then you probably won't need more than 750W.

Well, by what I've learned from the calculator, it seems that you're right. Those wattage levels are to the whole system. If it was only to the components, then everyone would be having 4-digit PSU wattages lol

[DMB2000uk]

AH, see you have used the efficiency rating on the wrong side of the calculation.

The meaning of the 85% efficiency is that for the PSU to give the computer 750W, it will have to draw 882W from your electric socket (750W = 85% * 882W).

However, the stated 85% efficiency is the lowest that that PSU does. So in actual use it will be at *least* that efficient, most of the time it will be more than 85% efficient.

Dan

[martini161]

http://educations.newegg.com/tool/psucalc/index.html

then you can figure out how much it will be pulling from the wall by (1+(1-E))W
where E= the efficency of the psu and w=the number the calculator gives you

[hnzw_rui]

Newegg's PSU calculator gives much higher estimated wattage than needed.

http://extreme.outervision.com/PSUEngine is much better and highly customizable to better reflect the actual system.

The following formulae were used to calculate estimated power draw:
Dan: Wattage/Efficiency
Martin: Wattage + Loss, where Loss = (1 - Efficiency)*Wattage

Unless efficiency is a hundred percent, it's obvious you'll get different values using the above formulae. So my question is, how exactly are efficiency ratings in power supplies computed?

[bandieramonte]

So I was having a misconception on the efficiency rating variable! Of course.... this was the piece that I was missing

So if the calculator from extreme.outervision estimates a 620 Watts usage for my system in the WORST case scenario, then I think that the toughpower 750 Watts is more than I need. So there is no reason to go for something greater than that. I can then go cool with this PSU. This alleviates me since I don't have to spend more than needed. The only little thing here is that this calculator does not allow me to estimate wattage if the video cards are overclocked... So if it's maximum 620 Watts without overclocking GPU's, then the MSI factory overclocked would be ?

Before learning all this, I thought that I needed a huge PSU because I always used to see people using PSUs of around 1000 Watts and they don't even have tri SLI setups or 4 ATI cards or more than one processor. But now I realize that they could have saved the unnecessary cash spent there.

[DMB2000uk]

That's right ^_^

Everyone always thinks bigger is better, when it isn't always the case.

Dan

[bandieramonte]

If my example system consumes 620 Watts at full load worst case, then how much would it consume in the same scenario if I overclocked the GPU's (two 8800 GTS G92) at a 12% core clock (650 to 730 Mhz core clock MSI factory overclock)? I had to ask this because the calculator doesn't have the option of overclocking GPU's.

Maybe it doesn't have that feature because overclocking 2 GPU's does not make much of a difference on wattage consumption?

[martini161]

Newegg's PSU calculator gives much higher estimated wattage than needed.

http://extreme.outervision.com/PSUEngine is much better and highly customizable to better reflect the actual system.

The following formulae were used to calculate estimated power draw:
Dan: Wattage/Efficiency
Martin: Wattage + Loss, where Loss = (1 - Efficiency)*Wattage

Unless efficiency is a hundred percent, it's obvious you'll get different values using the above formulae. So my question is, how exactly are efficiency ratings in power supplies computed?

yes but my formule is more acurate because dans formula is only computing the loss. you also have to add the watts used by the computer

[Zertz]

750W is more than enough ;)

[Major_A]

I didn't see it mentioned, though I skimmed...
With that 1200W PSU the efficiency would be terrible. You are better off looking at a 80+ Rated PSU in the 600-700W range.
Most of these will do fine, but some of them are JUNK.
http://www.newegg.com/Product/ProductLi ... rchInDesc=

[Zertz]

I didn't see it mentioned, though I skimmed...
With that 1200W PSU the efficiency would be terrible. You are better off looking at a 80+ Rated PSU in the 600-700W range.
Most of these will do fine, but some of them are JUNK.
http://www.newegg.com/Product/ProductLi ... rchInDesc=

You're right on the efficiency, but he can only choose between the 2 he mentioned though!

[Major_A]

Yep didn't see the country. In that case get the 750W. If you can, try to find a different brand though.

[KnightRid]

If you are that close for the 750 I still say go for the bigger one - I wouldnt go 1200, but you said you want to buy local and those are your only options.

Thats just me - I always want the extra available if i need it.

Mike

Its kinda neat to use the calculators and start plugging USB devices in ;)

My computer came up needing 650watts with only 1 video card using the extreme outervision one and the Q6600 since they dont even have the Q6700 listed except in extreme format

[ibleet]

You are smart to pick your parts so carefully. The Thermaltake 750 is a tier2 PSU and should be more than adequate. If it had been tier3 or lower, I would have said to go for the 1200, or choose another brand...even though I know you don't currently have that option.

[DMB2000uk]

Newegg's PSU calculator gives much higher estimated wattage than needed.

http://extreme.outervision.com/PSUEngine is much better and highly customizable to better reflect the actual system.

The following formulae were used to calculate estimated power draw:
Dan: Wattage/Efficiency
Martin: Wattage + Loss, where Loss = (1 - Efficiency)*Wattage

Unless efficiency is a hundred percent, it's obvious you'll get different values using the above formulae. So my question is, how exactly are efficiency ratings in power supplies computed?

yes but my formule is more acurate because dans formula is only computing the loss. you also have to add the watts used by the computer

Hnzw_rui: The efficiency of PSUs are calculated by placing a predefined load on the PSU (with special equipment pretending to be a PC), and measuring the wattage drawn by the PSU from the wall socket.

A forumula similar to Martini's is then used to calculate the efficiency; by the difference in power outputted and power drawn from the wall. The PSU is tested at different loads, from the minimum safe load to put on the PSU to the maximum safe load to put on the PSU, and the efficiency rating is usually decided by its lowest reading. PSU manufacturers (or sometimes really detail reviewers) will publish efficency graphs for PSUs. They tend to have the worst effeciency at the low loads and really high loads, with the best efficiency in the middle of their rated wattage output (so something like 350w being used by the PC on a 750w rated PSU).

Dan