Is 620w enough for SLi

Robert · 6 Jan 2007 at 17:47

sablabra said:
I just ordered corsair hx620w, and I'd be surprised if it doesn't handle 8800gtx sli. Each card draws about 150w and about 200w for cpu + mobo + hdd etc. That's 500w, and it can supply 50A, or 600w, on the 12V rail. I remember jonnyguru tested it with 40A from one connector without any problems whatsoever.
PS: I will only use one 8800gtx

I wouldn't recommend enermax galaxy because of the 5V and 3.3V ripple during high load on 12V rails.

Ripple can't be that bad otherwise they wouldn't sell it really. I bought the Galaxy 850 and it's great.

sablabra · 6 Jan 2007 at 18:02

Robert said:
Ripple can't be that bad otherwise they wouldn't sell it really. I bought the Galaxy 850 and it's great.

It exceeds the standard ATX specifications which allow up to 50mV ripple on 5V and 3.3V. The galaxy exceeds those limits during some what high load, and in my opinion that's not acceptable for such a pricey unit... Most manufacturers excuses them self with arguments such as the mobo or other units contain voltage regulators that will sustain and/or correct such ripple. True to a certain extent, but not all hardware are able to sustain it...

thefishdude · 6 Jan 2007 at 18:49

fornowagain said:
The overall wattage is meaningless. The only value that counts is the combined 12v. In the case of the Antec its a massive 52A (60A with the GTX mentioned). Don't go assuming 650W is a GTS SLi minimum, it not.

well im sorry i was just quoting what i could see as the recomended minimum as suggested by nvidia themselves. silly me i dint realise they posted useless information. :rolleyes:

fornowagain · 6 Jan 2007 at 19:22

thefishdude said:
lbut basically its 650min gts sli and 750 min gtx sli

thefishdude said:
well im sorry i was just quoting what i could see as the recomended minimum as suggested by nvidia themselves. silly me i dint realise they posted useless information.

You said 650W was a minimum for GTS. Its not, a 650W Antec of the model specified will work. Not all PSU are created equal. A more accurate statement would be a 650W PSU with 50A @ 12v as a minimum. I don't rate that as useless information.

thefishdude · 6 Jan 2007 at 19:34

i know they arnt all made equal . i just went by what was on nvidia site and that was the minimum spec of any of the psus listed for them cards.anways dont matter

he has been given info to get the correct psu thats all that matter s

fornowagain · 6 Jan 2007 at 19:43

thefishdude said:
i know they arnt all made equal . i just went by what was on nvidia site and that was the minimum spec of any of the psus listed for them cards.anways dont matter he has been given info to get *** correct psu thats all that matter s

As I said, the overall wattage of a PSU gives absolutely no indication of its suitability for the application. I'm not trying to trip you up, quoted PSU peak wattage values are often manipulated to look better than they are, modern power hungry PC's rely on the strength of the 12v supply. The less reputable manufacturer's in one way or another obfuscate the most significant (there are others) value, the combined 12v amperage.

Had3s · 6 Jan 2007 at 23:37

So, if the enermax ones aren't acceptable, any recommendations on a suitable modular 850-1000w replacement?

sablabra · 6 Jan 2007 at 23:40

Had3s said:
So, if the enermax ones aren't acceptable, any recommendations on a suitable modular 850-1000w replacement?

Seasonic M12 700w should be taken into consideration

. Although I personally believe 8800gtx sli would be fine with corsair 620w

Robert · 7 Jan 2007 at 10:42

Again - there are other factors in this. It maybe a problem with johnnyguru's testing, but I cannot see a company like Enermax getting away with it and having reputable companies selling their product. Other websites give it top notch marks. Anyway - what are the amps on the 12v rails (on the Corsair)?

sablabra · 7 Jan 2007 at 11:11

Robert said:
Again - there are other factors in this. It maybe a problem with johnnyguru's testing, but I cannot see a company like Enermax getting away with it and having reputable companies selling their product. Other websites give it top notch marks. Anyway - what are the amps on the 12v rails (on the Corsair)?

On the corsair 620w it is basically one big 12V rail which can supply 50A.

The problem with almost every single PSU review is that they have no way of testing it properly! Among those who test them properly are jonnyguru and spcr. Read here and see for yourself: http://www.hardwaresecrets.com/article/410

Btw, jonnyguru tested two 1000w units, and both had exactly the same problem...

Robert · 7 Jan 2007 at 11:14

I have an 850, so maybe the problem isn't an issue on it due to the lower power?

Oh and regarding the Corsair - I doubt 50amps would be enough as the recommended for a single GTX is 30 amps (what it actually uses is another story). If you have a bare system you get away with it - however [ui]iceman wasn't able to get his rig working on a 700watt PSU (OCZ or FSP, not sure which).

sablabra · 7 Jan 2007 at 11:23

Robert said:
I have an 850, so maybe the problem isn't an issue on it due to the lower power?

Oh and regarding the Corsair - I doubt 50amps would be enough as the recommended for a single GTX is 30 amps (what it actually uses is another story). If you have a bare system you get away with it - however [ui]iceman wasn't able to get his rig working on a 700watt PSU (OCZ or FSP, not sure which).

I know for sure 8800gtx sli have been tested on the corsair 620w with success, but it's not officially supported by nvidia. I also know for sure that one 8800gtx uses about 145w during load at stock speeds(which equals to 12A). So about 25A for the graphics cards alone, not too bad

Robert · 7 Jan 2007 at 11:25

Well Yellowbeard (Corsair support) has said that they've had SLI GTX cards running in the lab. It's just the uncertified bit that worries me, if it doesn't work you have no ground to stand on. For the cost of the Corsair I'd get the Enermax 850 (maybe the ripple isn't as bad on this)? I'm going to have a deeper look into this - but I can't see it being that bad as he still gives the PSU 9/10.

sablabra · 7 Jan 2007 at 12:32

Robert said:
Well Yellowbeard (Corsair support) has said that they've had SLI GTX cards running in the lab. It's just the uncertified bit that worries me, if it doesn't work you have no ground to stand on. For the cost of the Corsair I'd get the Enermax 850 (maybe the ripple isn't as bad on this)? I'm going to have a deeper look into this - but I can't see it being that bad as he still gives the PSU 9/10.

I'm not sure about the price in the UK, but where I live the galaxy 850w puts me back more than £180, while I just ordered the corsair 620w for £95.

He decided not to change the "numbers" he gave it, but he removed the "jonnyguru recommended badge".

fornowagain · 7 Jan 2007 at 14:43

Robert said:
Oh and regarding the Corsair - I doubt 50amps would be enough as the recommended for a single GTX is 30 amps (what it actually uses is another story). If you have a bare system you get away with it - however [ui]iceman wasn't able to get his rig working on a 700watt PSU (OCZ or FSP, not sure which).

30A is the recommended system power, not just the card. The theoretical TDP for a GTX is 177W. In total two overclocked GTX's are not going to use more the 30A between them. Capacity wise, a 50A PSU should be enough. It is possible to overload a PSU rail limiter depending on the configuration of the loads.

http://forums.overclockers.co.uk/showpost.php?p=8333533&postcount=43

sablabra · 7 Jan 2007 at 16:52

fornowagain said:
30A is the recommended system power, not just the card. The theoretical TDP for a GTX is 177W. In total two overclocked GTX's are not going to use more the 30A between them. Capacity wise, a 50A PSU should be enough. It is possible to overload a PSU rail limiter depending on the configuration of the loads.

http://forums.overclockers.co.uk/showpost.php?p=8333533&postcount=43

True, but the Corsair HX620W has no overload rail limiter! I personally asked jonnyguru about this, and he clearly explained it. He also tested a load of 40A from one connector without any problems.

This corsair unit is designed by seasonic, so I can imagine units like the M12s are built somewhat similar.

fornowagain · 7 Jan 2007 at 17:04

sablabra said:
True, but the Corsair HX620W has no overload rail limiter! I personally asked jonnyguru about this, and he clearly explained it. He also tested a load of 40A from one connector without any problems.

This corsair unit is designed by seasonic, so I can imagine units like the M12s are built somewhat similar.

I was referring to the FSP from the previous example. It states 15A rails, which may well be active as it didn't like SLi GTX.

fornowagain said:
If you look as rail 12V3, that's the MB and peripherals. 2X75W is going to PCIe slots from there, if the overcurrent really does trip at 15A/180W its not hard to see why.

sablabra · 7 Jan 2007 at 17:09

700w is somewhat useless if each rail is limited to 15A :rolleyes:

fornowagain · 7 Jan 2007 at 17:12

sablabra said:
700w is somewhat useless if each rail is limited to 15A

Are those rolleyes for me?

Look at FX700 12v3 rail in particular. With SLi thats 12.5/150w just to the PCie slots, wouldn't take much more load on a peripheral to trip it. Seems a bit daft feeding each PCIe 6 pin with 15A/180W when they're supposed to supply a maximum of 75W (although they do supply more, but not that much)

Personally from a PC design POV I would never advocate anything but a single rail. Its one of the reasons I use PCP&C. I'd rather manufacturers spent money on better stabilisation over OCP's anyday. Its worth remembering that manufacturers implement the ATX specification in different ways, some even ignore it. This article gives a little more info on 12v rail crosslroading.

http://www.extremetech.com/article2/0,1697,1932947,00.asp

sablabra · 7 Jan 2007 at 17:40

fornowagain said:
Are those rolleyes for me?

Look at FX700 12v3 rail in particular. With SLi thats 12.5/150w just to the PCie slots, wouldn't take much more load on a peripheral to trip it. Seems a bit daft feeding each PCIe 6 pin with 15A/180W when they're supposed to supply a maximum of 75W (although they do supply more, but not that much)

Personally from a PC design POV I would never advocate anything but a single rail. Its one of the reasons I use PCP&C. Its worth remembering that manufacturers implement the ATX specification in different ways, some even ignore it. This article gives a little more info on 12v rail crosslroading.

http://www.extremetech.com/article2/0,1697,1932947,00.asp

Lol, that smiley brings nothing but hostility to the forums