PSU advice

[poonsies]

Hi everyone,

My current setup is:

4400+ AMD Cpu
A8N32SLI Deluxe Motherboard
2gigs DDR Corsair performance ram
3 HDs ( 1TB,1 250gig, 1 74gig Raptor )
1 x 8800GT
7 x 80mm case fans ( could probably cut this to 3 if it helps)
1 DVDRW drive

I decided to buy a second 8800GT to run in SLI with the current one I already owned. I had a Tagan 580watt psu (null) which seemed to run the 2 cards fine. After 30 minutes of testing with 3dmark etc I decided to play some Left 4 Dead, 5 minutes in there was a loud bang and a definate smell of burning, the PSU had blown.

Anyway, a friend of mine has a spare 600watt OCZ PSU (null) which i could use.

I guess what i am asking is:

a) Did my old PSU explode in that way because the power draw was too great ? Is that a normal way for an underpowered PSU to fail ?

and...

b) Am I risking the same thing happening to the 600watt OCZ PSU ? Is it enough to run the rig I have along with 2 8800GT in SLI ?

Thanks in advance for any help =)

Sean,

 

[Zap]

Hi poonsies and welcome to Anandtech Forums.

Your Tagan only had 32A (384W) of power for the +12v rails. The OCZ has 44A (528W). Since PCIe graphics cards use only +12v, you can see that the Tagan was a bit lacking. The other thing is that PSUs may weaken with age, plus I'm not sure what temperature those two PSUs are rated at. For instance, if you have PSU A which is 500W rated at 25ºC and PSU B which is 500W rated at 40ºC, once in your computer with 40ºC temperatures inside your case PSU B can still put out 500W while PSU A may only be capable of putting out 400W.

Anyways, here are some answers:

a) Yes, possibly the power draw on the +12v rail was too much for your PSU. Yes, some PSUs will "POP" when loaded too high.

b) Yes you are, but since the OCZ has much more of the rated power on the +12v, I think it will do a lot better than the Tagan.

 

[poonsies]

Hi and thanks for the speedy reply!

Could I ask how you work out the power for the +12v rails ?

 

[HOOfan 1]

Originally posted by: poonsies
Hi and thanks for the speedy reply!

Could I ask how you work out the power for the +12v rails ?

The label should tell you. Although I have looked up several sites and both of them say it has 2 12V rails with an OCP limit of 20A each and a combined limit of 32A. A combined power limit of 420W...which shows someone didn't know what they were doing when they made that chart.

Power(watts)=Electrical potential(volts)*current(amps)

If it has a combined limit of 32A then as Zap said, that is 384W not 420W.

Whoever made that chart, made the same mistake many, uninformed people do, they added the two 12V rails together. Those 20A ratins on the individual rails are artificial ratings set up by circuitry. If that circuitry was not in place then instead of showing as two rails with a 20A limit, it would show as a single rail with a 32A limit. The reason they are split into two rails with a higher limit than 16A (32A/2) is because the designers are making sure that components on a single rail are not starved of power.

 

[poonsies]

Well thank you for the help so far, I stuck in the 600 watt OCZ and the system still struggled ( showing itself in the form of black screen hangs ). Taking out the 2nd 8800GT solved this problem so I have bitten the bullet and decided that buying a new PSU will have to be done. I was looking at the Corsair 850W TX (http://www.scan.co.uk/Products...2-PSU-5-Year-Warranty) as its glowing reviews, 5 year warranty and slight future proofing for upgrading my system later on in the year all appealed. Coming in at £114 delivered is this PSU one I should consider or are there others you might recommend ?

Thanks again for all the help.

Sean.