PSU load correction?

joemadeus · Post by **joemadeus** » Mon Jul 04, 2005 9:54 am

If I'm computing the total wattage for an entire system in a worst-case-scenario, and want to come up with a more realistic view of the figures by adjusting for the fact that NOBODY can force a machine to use 100% of that figure, what sort of correction does everyone use? I'm figuring 80% -- but that may be way off.

I reproduced an excel spreadsheet with the figures I'm using below. At the very bottom the watt figures are multiplied by 1.25 to account for PSU efficiency (assuming 80%). Taking .8 of that figure for the correction means going back to 404w, of course.

If anyone has any input on my figures, I'd love to hear it. And I put all the power for the memory, motherboard and CPU on the 12v2 supply -- is that reasonable?

Thanks!

-j

Code: Select all

Desc.     Part              +3.3v     +5v     +12v1      +12v2     
----------------------------------------------------------------------
CPU       Pentium-M 760                                     27     
Mobo      i915GMm-HFS                            72     
RAM       OCZ DDRII pc4200                       33     
Video     Gigabyte 6600GT      10                66     
Drives    Hitachi 7k80                 10        44          
Fans      Panaflo 80 & 120                        5          
DVD       Sony D26W                     7.5      18          
USB       8 on Mobo                    40        
Firewire  1 on Mobo                              15     
PCI Tuner Hauppage PVR150      25      25         6              Total
----------------------------------------------------------------------
Total (W)                      35      82.5      67         27    404
Total (A)                      10.6    16.5      21.6        2.3     
----------------------------------------------------------------------
W @80% Eff.                    44     103        84        274    504
A @80% Eff.                    13.3    20.6      27.0        2.8   
----------------------------------------------------------------------

Tephras · Post by **Tephras** » Mon Jul 04, 2005 11:00 am

When calculating total system power draw AMD suggest 100% for CPU and 80% of maximum power draw for the other components. There's no need to account for PSU efficiency.

The 12V2 line is only for CPU, all other components that use 12V gets it from the 12V1.
Your amperage figures does not match up with the wattage figures, if the amperage are rounded off you should round them off upwards since the total amperage on each rail is of more importance when you're trying to decide what PSU to get.

Does your motherboard really use that much power? And do you actually have 8 USB devices connected at the same time?

Devonavar · Post by **Devonavar** » Mon Jul 04, 2005 11:10 am

Where are you getting that 72W figure for the motherboard? I have to say that looks like it's off by say 60W or so. Your mobo uses only 10-15W. I would bet your RAM doesn't use 33W either, but I'm less aware of RAM power draw.

Other figures that look high:
-HDD (shouldn't draw that much, even at spinup)
-PCI Tuner: Does this have a large heatsink and/or a fan? If it doesn't there's no way it's drawing 50W+. I believe 10W is a more reasonable estimate for this card.

Also, the ONLY load on the +12v2 rail should be the CPU. All other 12V loads go on +12v1.

There is NO WAY your P-M system is going to draw 500W AC. The highest AC power draw I have ever measured was 313W, and that was with a P4 670, 6800GT and 4HDDs running three simultaneous benchmarks (two for the CPU, one for the GPU). I probably could have spiked it slightly by seeking the drives or burning a CD, but not by more than 15-20W AC.

Based on my experience with P-M systems, I'd be surprised if your configuration topped 150W AC. Take a look at the SPCR PSU Fundamantals article for more information about realistic power draws.

joemadeus · Post by **joemadeus** » Mon Jul 04, 2005 11:17 am

Tephras wrote:The 12V2 line is only for CPU, all other components that use 12V gets it from the 12V1.

Does that mean that memory and nb/PCIe/etc are powered from the v1 line? I thought the v2 line supplied both the 2x2 and the 2x10 connectors that go onto the board. Sounds like I'm wrong. If this is the case, I'll need 20A on the v1 line, which sounds like a lot of power.

Tephras wrote:Your amperage figures does not match up with the wattage figures, if the amperage are rounded off you should round them off upwards since the total amperage on each rail is of more importance when you're trying to decide what PSU to get.

All of this was done in excel with formatting that rounds the 1/10ths of watts. I simply dropped the 1/10ths of amps when copying the data into the table, so I do have "rounding" errors -- I'll go edit that table so it's correctly rounded. The total wattage figures (404 & 504w) should be the correct total

Tephras wrote:Does your motherboard really use that much power? And do you actually have 8 USB devices connected at the same time?

To tell truth, I can't even think of eight different USB devices to power at ALL, let alone at the same time. Let's see... mouse, keyboard, camera, monitor info, battery backup info... Well, I didn't actually think I'd be powering all 8 lines at the same time, but I figured it's supposed to be worst-case. Maybe I erred a little too much on the 'worst' side.

Devonavar, I did see the article you mentioned and it would be nice if I could draw so little power, but that 6600GT alone wants 75w at full-tilt and I wouldn't mind doing a little overclocking on both the CPU and the GPU. I expect 200-250w power draw during normal usage, which should put it in a good efficiency zone when using a Seasonic S12-430. This whole study was brought on by trying to figure out which of those models supplied the juice I need on the v1 and v2 lines.

-j

joemadeus · Post by **joemadeus** » Mon Jul 04, 2005 11:45 am

The figures for the CPU, hard drives, fans, and DVD-RW drive were taken from specs I found either on the mfgr's site or on the Web (usu'ly at retailer info pages.) The figures for the PCI tuner and PCIe video cards are for max draw on the 3.3v, 5v and 12v PCI lines; neither Hauppage nor Gigabyte had figures and I couldn't find anything else. The figures for USB and firewire ports are from their specs, and assuming they're powering their devices full-tilt. The figures for the RAM were taken from the JEDEC DDR-II spec. The figure for the motherboard were apparently taken from thin air, since I have no idea where I came up with that. I think I used the Intel i915GM spec as a starting point. This was before I had my first cup of coffee, so it's more than likely complete bull.

You're right, I should have compared my figures to the page you mentioned before posting (which I've known about) -- it would have been a good ballpark comparison, at least.

-j

Devonavar wrote:Where are you getting that 72W figure for the motherboard? I have to say that looks like it's off by say 60W or so. Your mobo uses only 10-15W. I would bet your RAM doesn't use 33W either, but I'm less aware of RAM power draw.

Other figures that look high:
-HDD (shouldn't draw that much, even at spinup)
-PCI Tuner: Does this have a large heatsink and/or a fan? If it doesn't there's no way it's drawing 50W+. I believe 10W is a more reasonable estimate for this card.

Also, the ONLY load on the +12v2 rail should be the CPU. All other 12V loads go on +12v1.

There is NO WAY your P-M system is going to draw 500W AC. The highest AC power draw I have ever measured was 313W, and that was with a P4 670, 6800GT and 4HDDs running three simultaneous benchmarks (two for the CPU, one for the GPU). I probably could have spiked it slightly by seeking the drives or burning a CD, but not by more than 15-20W AC.

Based on my experience with P-M systems, I'd be surprised if your configuration topped 150W AC. Take a look at the SPCR PSU Fundamantals article for more information about realistic power draws.

joemadeus · Post by **joemadeus** » Mon Jul 04, 2005 12:31 pm

I updated the figures for a more realistic point of view, but still worst-case. Here's the new table:

Code: Select all

Desc.     Part              +3.3v     +5v     +12v1      +12v2     
----------------------------------------------------------------------
CPU       Pentium-M 760                                     27     
Mobo      i915GMm-HFS                            15     
RAM       OCZ DDRII pc4200                       33     
Video     Gigabyte 6600GT      10                66     
Drives    Hitachi 7k80                 10        44          
Fans      Panaflo 80 & 120                        5          
DVD       Sony D26W                     7.5      18          
USB       8 on Mobo                    10        
Firewire  1 on Mobo                              15     
PCI Tuner Hauppage PVR150       0       7.5       3.5            Total
----------------------------------------------------------------------
Total (W)                      10      35.0     200.5       27    272
Total (A)                       3.0     7.0      16.6        2.3     
----------------------------------------------------------------------

This seems MUCH closer to me, especially given my current situation: I'm trying to run exactly this in a 250w PSU, but find that the machine freezes every time I try to run too much. Works fine if I don't try running Rome: Total War or SETI@Home, either of which, by these figures, would put it over the 250w limit for the PSU.

Seeing this table this way, however, makes me wish Seasonic didn't divide the two 12v rails. The draw on the v2 rail is going to be light. I'll have to buy a power supply that's larger than I would have if they were combined, just to feed the video card and drives.

-j

Devonavar · Post by **Devonavar** » Mon Jul 04, 2005 1:06 pm

Have a look at this thread for info on the power draw for the 6600GT. ~50W max is about right, taken from this X-Bit Labs article.

Also, I have a hard time believing your drives are consuming 50W+ at startup, and I question the relevance of using this rating anyway. If your system is booting fine off a 250W PSU, the instability is not a result of the startup load. I also don't trust Hitachi's specs for idle, I've never seen a drive draw more than 16W at full seek, tested according to the methodology in this article. For reference, Hitachi's 7K250 measured 13.1W at peak (seek), and the 7K400 measured 15.5W. You can assume a 30-70% split between the 5V/12V lines.

I think if you're really interested in finding out how much power you need, you should invest in an AC meter (e.g. a Seasonic Power Angel or Kill-A-Watt), and actually measure how much power you're using. Assume ~70% efficiency for your 250W PSU, so multiply whatever you get by 0.7 to get the DC draw.

Post by **MikeC** » Mon Jul 04, 2005 2:19 pm

joemadeus wrote: I'm trying to run exactly this in a 250w PSU, but find that the machine freezes every time I try to run too much.

-j

Ditto Devon's comments, and emphasize this: His numbers are AC input to the PSU, not DC power output from the PSU. The 313W AC peak he mentions is equal to 250W DC output -- and this from Intel's most power hungry 115W TDP processor, a 6800GT, 1G ram & 4 HDDs.

272W DC for your system??

---- absolutely no way.

I would be amazed if you could get even 150W DC power draw out of your system no matter what you tried to run with your combination of components. If you could make everything run 100%, maybe, but the reality of any OS is that this is impossible, and you'd find it excruciatingly frustrating to work with a machine that's trying to multitask like that. (except mebbbe with a multi core/CPU machine).

Also, all 250W PSUs I know of go back to ATX12V PSU spec V1.1 or earlier -- they have low 12V current capacity and much higher 5V & 3.3V. You're probably overloading your 12V line while the other lines sit idle. I'd suggest trying an efficient recent version SFX PSU rated at 250W or higher (Seasonic has a 300W version) or a 300W ATX12V v1.3 of higher. This will be plenty of power.

joemadeus · Post by **joemadeus** » Mon Jul 04, 2005 2:58 pm

MikeC wrote:Also, all 250W PSUs I know of go back to ATX12V PSU spec V1.1 or earlier -- they have low 12V current capacity and much higher 5V & 3.3V. You're probably overloading your 12V line while the other lines sit idle. I'd suggest trying an efficient recent version SFX PSU rated at 250W or higher (Seasonic has a 300W version) or a 300W ATX12V v1.3 of higher. This will be plenty of power.

Well, I did find a Seasonic SS-300SFD (you know it well, MikeC, and thanks for suggesting it on the i915GMm review forum) but it's only found in Japan and Europe and, when in Europe, sold under the Soltek name. It's 35 British Pounds for shipping alone -- that's roughly $60 -- not including the 42 B.P. (around $70) for the unit itself. They appear to be unavailable in the US, and Seasonic hasn't responded to two of my inquiries on their Web-based form nor to my email. I don't have much incentive to buy that unit

.

If I'm going to lay down that kind of money (which I am, one way or the other, since I don't buy machines very often and I like to make sure they're going to last) I'm thinking it might be a better idea to just buy a new, smallish case that'll take a mATX motherboard and an ATX PSU. Here's the one I'm thinking about (http://aspireusa.net/product.php?pid=14 ... 9d6940d241) yes, in green, because I like the pimp thing, it'll go with my decor, not to mention that it's relatively small and I should be able to mod the windows to include a blowhole/intake vent should I need to. It'll also let me mount a slightly larger heatsink on the CPU which, much to my chagrin, I apparently need. I have a Sony DVD player, so it should provide enough clearance for its connectors even with an oversize ATX PSU in there.

Speaking of which, I'm thinking about Antec's Phantom 350 for this, shady reject history be damned. My old computer had a trio of U160 IBM DDYS drives in it, and I plan on overcompensating for their loud-ass seeking and parking. A no-dB PSU sounds like just the thing.

-j

Post by **MikeC** » Mon Jul 04, 2005 4:25 pm

My advice would be to try a Seasonic S12 or Super Tornado. The S12, especially, is a proven ultra quiet PSU. And I just discovered that SeasonicUSA now has a store attached, and they sell warrantied refurbished units at very good prices! http://store.seasonicusa.com/ (if you decide to try their $25 refurbished S. Tornado, just make sure it is a rev.A3)

joemadeus · Post by **joemadeus** » Wed Jul 06, 2005 12:15 pm

MikeC wrote:My advice would be to try a Seasonic S12 or Super Tornado. The S12, especially, is a proven ultra quiet PSU. And I just discovered that SeasonicUSA now has a store attached, and they sell warrantied refurbished units at very good prices! http://store.seasonicusa.com/ (if you decide to try their $25 refurbished S. Tornado, just make sure it is a rev.A3)

Yeah, I saw that new site and the store and was tempted to buy one of the S12s. I saw your reviews of them, too, of course. But, in the end, I wound up giving a Phantom a try, for two reasons:

1. The supply I have now is 10A on the 12v rail, like you said it would be, and it's just not enough power (for that rail). To get more juice than this from an S12 I'd have to buy the 430w version (14A on 12v1), with all of the additional (admittedly slight) fan noise.
2. I'm intriqued by the the 'no PSU noise' idea. My last machine, like I mentioned, was UNBELIEVABLY loud. That they have a troubled reject history bothers me, but it seems like they finally got it (mostly) right... maybe.

It's really too bad I have to get rid of the older mATX case -- I like them a lot. (TTGI's TT-101 case: http://www.ttgiusa.com/product/pccase/sf-101s.htm)

-j