PSU for Xfire system

[fornowagain]

I see your point, but the individual 12v are only ~14A each.

Those numbers are only arbitrary nonsense, it’s only a 240VA current limiter, they all are (99% anyway, in fact I don't know of any real dual rails TBH). The way they rate them is just spin. Look at the total combined maximum wattage for the 12v.

Each rail will pull to a maximum 20A (or more, some are set higher anyway). You can't get more out than you put in. If the maximum wattage is, say 360W(12v) then the PSU can supply 30A(12V).

Assume a dual rail. That could be 15A per rail. Or 20A + 10A. And you can’t just add the specified rails together either, like if it says 12v1=18A 12v2=20A, that’s not 38A.

The problem is if the components pull more than 20A on one rail, like CF 1900’s. Then if the manufacturer has been very strict, the rail OCL will trip. That’s why more rails or one rail is better than dual rails. The Silverstone/FSP IIRC has each graphics PCI-e on different rails, no way is it going to get to 20A on a single rail per GF card. Like this:

+12V1(13A) : CPU1
+12V2(18A) : CPU2+SATA
+12V3(16A) : MB+VGA1
+12V4(18A) : HDD+VGA2

And ignore the total PSU wattage, it meaningless, more hype. Some lower wattage PSU kill the bigger ones. Add up your 12v current load, then add a bit for losses and match the 12v total wattage available on the PSU you fancy.

 

[weescott]

I killed a 600w Enermax noisetaker with 1 7800GT and an X2 3800 @ 2.8. 700w seems sensible to me.

 

[fornowagain]

I killed a 600w Enermax noisetaker with 1 7800GT and an X2 3800 @ 2.8. 700w seems sensible to me.

Sorry, but I doubt it. You can't have overloaded the PSU with those two. The X2 overclocked uses maybe 10A/120w the GT use less, 6.6A/80W. Dunno which one, but the Enermax EG701AX is good for 35A/420W@12v. That more than enough for most systems. Unless you've got a LOT of hard drives

 

[turbotoaster]

you need a total of at least 55A and 25a on each rail, if ya want to overclock your cards and cpu, thats whats holding me back at the moment, when i get the 1k PSU im going for 17k in 05

ive got a TAGAN 580w which is 36A single or 20A on each rail

 

[barney]

Ive got the epsilon in a x1900xtx xfire system, duel core 4800 CPU, 3 sata drive and 1 optical drive and it runs perfectly (with LOADS of fans on it too).

Im in the middle of overclocking my system at the moment and so far it is holding out ok. CPU is at just over 2.6GHZ and at the moment one of my video cards is clocked to 680/780 at 1.45 volts and all seems stable (still working on upper/testign the memory on that card).

I tried a few PSU's before and none of them worked even at stock.

 

[fornowagain]

you need a total of at least 55A and 25a on each rail,

The OP should calculate the loads like this overclocked example. All 12v currents, it's all that really matters with an AMD64 system. Your not going to bother the 3.3V/5V rails for much tbh.

Opteron 170 @ 2.8GHz 1.55v = 190w (Stock 110w) the over voltage ups the wattage. It may be less.
Motherboard approx ~ 45w
X1900XTX say 700/850 = 145w (95% is 12v)
X1900XTCF = 107w second card isn't running flat out, say max 75% of first.
Xfi ~ 8w
2 Raptors (0.35mA @ 12v sustained, but startup goes way higher maybe 2A ) = 48w at spin up, 8.4w at load.
2 SATA 7200 RPM (0.5mA @ 12v, 1.8A at startup) = 44w start up, 12w at load
1 optical drive system = 17w
1 FDD = 5w
3 x 92mm fans ~ 36w
2 usb devices ~ 5w

What's that just using generic values? 55A/650w all on the 12v. If everything started at once and went to full load Which of course they don't. Take the hard drives at the sustained read/write values, not the spin up and that's 48A/580W (12V) still not quite right. For power calculations its normal to include factors for diversity (i.e not everything runs flat out all together), loss (inc derating) and efficiency. I usually work on stuff a bit bigger than a PC, but say the running load is only 80% of maximum, but the losses to heat and resistance are 5% and the PSU is down 5% from age (or its not a review sample). At a conservative estimate say you need 90% of the maximum load 43A/520w at 12v. And remember that's now a constant sustained load, not a millisecond peak value. Watch it, because some firms like to quote peak or they rate the unit in a freezer. Look for the ones rated at 50C, PSU's derate very quickly, like 10W/C or -100W for a delta of 10C and so on.

That's still quite a load, more than a lot of PSU can handle. You don't need 25A on all rails, 12V1 is supposed to be for the CPU only in ATX, that's going to need 16A. Some of the newer PSU's like the FSP FX700-GLN will be able to handle it. £103 (inc) with 4 rails and 50A/600w (12V) And the PCI-e are connected to different rails so they can't reach the 240VA limit.

FX700-GLN
12V1 - CPU 1
12V2 - CPU 2, PCIe 2
12V3 - Motherboard, SATA, 4-pin molex
12V4 - PCIe 1

Still if you can afford £300/£350 for the 850w/1kW PCP&C, I would, they are the best.

 

[turbotoaster]

The OP should calculate the loads like this overclocked example. All 12v currents, it's all that really matters with an AMD64 system. Your not going to bother the 3.3V/5V rails for much tbh.

Opteron 170 @ 2.8GHz 1.5v = 190w (Stock 110w)
Motherboard approx ~ 45w
X1900XTX say 700/850 = 145w (95% is 12v)
X1900XTCF = 107w second card isn't running flat out, say max 75% of first.
Xfi ~ 8w
2 Raptors (0.35mA @ 12v sustained, but startup goes way higher maybe 2A ) = 48w at spin up, 8.4w at load.
2 SATA 7200 RPM (0.5mA @ 12v, 1.8A at startup) = 44w start up, 12w at load
1 optical drive system = 17w
1 FDD = 5w
3 x 92mm fans ~ 36w
2 usb devices ~ 5w

What's that just using generic values? 55A/650w all on the 12v. If everything started at once and went to full load Which of course they don't. Take the hard drives at the sustained read/write values, not the spin up and that's 48A/580W (12V) still not quite right. For power calculations its normal to include factors for diversity (i.e not everything runs flat out all together), loss (inc derating) and efficiency. I usually work on stuff a bit bigger than a PC, but say the running load is only 80% of maximum, but the losses to heat and resistance are 5% and the PSU is down 5% from age (or its not a review sample). At a conservative estimate say you need 90% of the maximum load 43A/520w at 12v. And remember that's now a constant sustained load, not a millisecond peak value. Watch it, because some firms like to quote peak or they rate the unit in a freezer. Look for the ones rated at 50C, PSU's derate very quickly, like 10W/C or -100W for a delta of 10C and so on.

That's still quite a load, more than a lot of PSU can handle. You don't need 25A on all rails, 12V1 is supposed to be for the CPU only in ATX, that's going to need 16A. Some of the newer PSU's like the FSP FX700-GLN will be able to handle it. £103 (inc) with 4 rails and 50A/600w (12V) And the PCI-e are connected to different rails so they can't reach the 240VA limit.

FX700-GLN
12V1 - CPU 1
12V2 - CPU 2, PCIe 2
12V3 - Motherboard, SATA, 4-pin molex
12V4 - PCIe 1

Still if you can afford £300/£350 for the 850w/1kW PCP&C, I would, they are the best.

thats what my pennies are saving up for 1k, drooling just thinking about it

 

[pcoltrane]

Do any of you guys pay your own electric bills?
I'm not happy with my media centre pcs using <50W idle and 80W full load (including PSU losses) or my main PC using 200W. Running a house of 4 or 5 Pcs,2 of them 24/7 a serious chunk of my electric bill is down to the pcs

700W 24/7 = approx £613 a year in electricity

It's great that AMD and intel are finally focussing on performance per watt ... but gfx cards have gone mental. I'm no green fanatic, but it strikes me as crazy that top cards are using more than 100W each (more when you consider PSU losses). Maybe it's time there were some limits imposed - I guarantee that because power squares with voltage increase they could cut output in half but only lose at most 10% of the perfomance. Would we miss i if we never had it?

Sorry for hijaking the thread!

Marc

 

[fornowagain]

Do any of you guys pay your own electric bills?

Sorry for hijaking the thread!

Marc

Yes unfortunately. And it's way more than 700W @ 230Vac for one of these uber rigs. Remember that these PSU ares supposed to be 80% efficient. They're not, take an OCZ 600W, its about 65% IIRC. So for every 700W supplied it consumes 1kW.

Do I care? A bit, but not that much. You don't run it at full tilt 24/7. I'm of the opinion that if you bought a £2500 PC to play games and you can't afford £250 for electricity then you should have bought an XBOX.

 

[Melkor]

Another hijak !!

I am making a similar system except only 1 Asus x1900xt-x and a 4800+.
Will a Enermax Liberty 500W be enough to power this ? I was initaly getting a Tagan 580 but it seems to be out-of-stock now.

 

[fornowagain]

Another hijak !!

I am making a similar system except only 1 Asus x1900xt-x and a 4800+.
Will a Enermax Liberty 500W be enough to power this ? I was initaly getting a Tagan 580 but it seems to be out-of-stock now.

Do the math, it's the only way.

 

[goreblast]

I do indeed pay my own electricity bill at normally £300 per quarter, has been as high as £420 !!!