8800GTX power supply?

[simon11]

I bought a new computer a few months ago a Core 2 duo with one 8800GTX card. I asked for a power supply that would run two cards in SLi for future use. They put me in an Atrix 600T 720w which I questioned at the time but they said it would do the job o/k.

I have only one card installed but if my computer is on for any length of time and I play even a slow game like pool or Tiger woods golf. My computer keeps dropping back to the desktop with the message that there is not enough power to the card and that it has been slowed down to protect my computer. The twelve volt rail is only at 11.6 volts. Is this normal? Or is my power supply underated or faulty?





Thanks for any reply.



Simon.

[Joe Forster/STA]

Yes, it is normal that a voltage that is supposed to be X Volts is actually around X-0.5 - X+0.5 Volts; electronic equipment is prepared for such differences. Also, if it's a switching power supply then you won't be able to measure exact values if there's no real equipment connected to it, only your voltage meter/multimeter.

[Sidney]

You only bought it a few months ago.

First stop for your problem should be where you bought it from, not a forum.

[DABhand]

Unfortunately not all high end PSU's have the necessary ampage on the necessary rails to supply high end GPU's.

And its not easy to know for people if they do or not, its a bad time at the moment for that since there is no general design for GPU's, since ATI and Nvidia cards do things differently.

They should get together and actually come up with a permanent solution to the problem so it doesnt cost the consumer a lot of money on trial and error.

[simon11]

Originally Posted by Sidney

You only bought it a few months ago.

First stop for your problem should be where you bought it from, not a forum.

They are not likely to be honest in the matter. I asked for a power supply that would run Two 8800gtx cards although I could only afford to purchase one at the time. I now find although the power supply is a 720w it only has two 15 amp rails. This is nowhere near the spec required for sli use. The spec is at least 2 30amp rails.
I have just ordered a Thermaltake Toughpower 1000w power supply. It has four rails. 2 at 20amp and 2 at 36amp. More likely to do the job.
The firm seemed Legit at the time but I have been conned. The power supply they fitted retails at £45.00. The One I am buying retails at over £200.00. But I have managed to get one for £140.00 which is a great deal.
I never did intend to have it repaired under warranty as I would have to pack it up and send it back. I would rather just buy the bits if necessary. I didn't imagine any trouble anyway.
I should have plenty of surplus power when I get this in the case. No wondering if it is big enough. I would have ordered one in the first place but the largest supply they listed was the 720w. They told me it would do the job! Obviously wrong information. They must be novices.


Forums are usually very helpful and the members are usually more knowledgable and honest with their views!
Enough said!

[simon11]

Originally Posted by DABhand

Unfortunately not all high end PSU's have the necessary ampage on the necessary rails to supply high end GPU's.

And its not easy to know for people if they do or not, its a bad time at the moment for that since there is no general design for GPU's, since ATI and Nvidia cards do things differently.

They should get together and actually come up with a permanent solution to the problem so it doesnt cost the consumer a lot of money on trial and error.

Thanks for this info. You certainly make a good point. The firm that supplied mine probably were not even aware that it would not do the job.

[BarryB]

I've got a PC Power & Cooling 750w PSU, capable of supporting two GTX's in SLi!

It has a SINGLE 12v rail that supplies 60A, not a split rail that divides the amps across the rails, so with my PSU all the amps are available to the system, no amps are trapped on rails that don't use all the amps!!

Getting a SINGLE rail PSU is the way to go, at least for me!

[DABhand]

Originally Posted by simon11

Thanks for this info. You certainly make a good point. The firm that supplied mine probably were not even aware that it would not do the job.

Motherboards come into it also.

Someone came to my shop, wanted a nice 600w+ silent PSU (i.e. no fan but heatsinked). Gave him one that had 45amp rail. He came back with the PC complaining I sold him shoddy goods.

He had an Asus K8V-SE Deluxe (a 754 socket AMD board), would run okish on XP with his ATI card, but when he tried to install Vista it would bluescreen on install.

So for a laugh I changed the motherboard to a gigabyte board I had lying around, Vista installed no problems at all.

The Asus board was fine it wasnt faulty etc. It was like it sucked the life out of the PSU.

So again another reason why ATI and Nvidia need to get together to form a solution on an exceptable state of things for GPU's.

[simon11]

Originally Posted by BarryB

I've got a PC Power & Cooling 750w PSU, capable of supporting two GTX's in SLi!

It has a SINGLE 12v rail that supplies 60A, not a split rail that divides the amps across the rails, so with my PSU all the amps are available to the system, no amps are trapped on rails that don't use all the amps!!

Getting a SINGLE rail PSU is the way to go, at least for me!

Your power supply will work if you don't put too much in the computer or the single rail can be overloaded and you can get crashes especially when overclocking everything. recommended sli boards have more than one rail. If the cards have their own supply rail nothing else will interfere with them.
It also states that the cards should be on their own rail. Not shared.
The amps rating is as important as the Watts.

[BarryB]

PC Power & Cooling are among the 'elite' of PSU's

Read this: http://www.pcpower.com/technology/myths/

and note number 8. ARE MULTIPLE 12-VOLT RAILS BETTER THAN A SINGLE 12-VOLT RAIL?

I thought more rails was good until I read that, then read reviews and forums and came away with the feeling that Single Rail PSU's are better! But, you buy what you want, I'm only pointing out Mulit-Rail PSU's aren't all they are cracked up to be!

[simon11]

Originally Posted by BarryB

PC Power & Cooling are among the 'elite' of PSU's

Read this: http://www.pcpower.com/technology/myths/

and note number 8. ARE MULTIPLE 12-VOLT RAILS BETTER THAN A SINGLE 12-VOLT RAIL?

I thought more rails was good until I read that, then read reviews and forums and came away with the feeling that Single Rail PSU's are better! But, you buy what you want, I'm only pointing out Mulit-Rail PSU's aren't all they are cracked up to be!

Very interesting reading. It appears that the only advantage of several rails is less dammage if something is wrong and less noise in the supply. However because I have bought a 1000w supply with a total of 112amps on four rails I will probably only use just over half with everything running. So it should run nice and cool and quiet!

[BarryB]

If a split rail has enough amps on it then there's no problem, it's when they DON'T put enough on it causes problems!

My PSU is quiet and hardly gets warm when playing games!

Using a wattage calculator I think in total I'm only drawing 380w from the PSU:

Asus Crosshair mobo
AMD 2.8GHz Dual Core with Arctic Freezer HSF
2GB Ballistix DDR2 RAM
nVidia 7950GT
SBLive 5.1
RocketRaid IDE Controller
3 x HDD
2 x DVD
1 x Floppy
5 x 80mm case fans
Wireless Mouse + Wired Keyboard

Plenty of watts left for when nvidia release the 9800

[simon11]

I have just ordered a voltage and watt monitor that plugs in the wall socket. It will be interesting to see what the power is I am using?

[BarryB]

Would be interesting, you could then use an online wattage calculator and see how far off they are from an actual plugin one!

[simon11]

Originally Posted by BarryB

Would be interesting, you could then use an online wattage calculator and see how far off they are from an actual plugin one!

Good idea! I will try it. I haven't fitted the new power supply yet as I want to check out the efficiency. I will check the usage on my existing supply when I get the monitor and then when I change over I will see if there is any difference as the new power supply is supposed to be more efficient. It might be minimal but I would like to know if the advertising about saving electricity is correct.