730 watt PSU enough to power GTX 780.

[leo1230]

Hi, i have a Be Quiet Pure Power L8 PSU rated at 730w, on the box it states that it does 330 watts over the 12v Rails. this works out at 28a per rail.

when i look at websites to see if the amperage is enough, some of them say that it needs 42a over the 12v rail. would i need a new PSU for this graphics card, use two of the modular wires to power it or will the 1 cable with a 6 pin + 8 pin work.

I wouldn't like to use both cables as one of the 12v rails is powering the cpu too and review recommend not to use it unless necessary.

thanks.

 

[Dark Lord of Tech]

A GeForce GTX 780 needs 42 amps on the 12v rail and a 600 watt power supply.

Your power supply has more than enough power to run a 780.

http://www.techpowerup.com/reviews/beQuiet/PurePower_L8_730W/

Here's a review of your supply ^

 

[jimthenagual]

According to THIS PAGE, your PSU puts out 660W on the +12v rail, which gives you 55A.

Is this your sticker?

 

[InvalidError]

It does not "need" 42A - that figure includes 12-15A for everything else in your PC on top of the GPU's own worst-case ~23A and a margin on top just in case.

Since the GTX780 can peak at ~250W, you would need to use the whole 6+8 configuration.

 

[leo1230]

Cant believe I Missed it, doing the maths at 330 / 12 = 27.5, I thought it was too low. Guess 1 Cable with 2 connections counts as 2 times. I couldnt actually get to my PSU to read it, although above the 55a bit it says 30a per rail, wouldnt that be more accurate or is it 30a for 6pin + 30a for 8 pin?

Can Anyone Explain too why the Sticker shows 730watt PSU, but adding the numbers above i get closer too 830w?, its something ive always wondered since buying it.

1 more thing, although the amps are right, would my PSU be enough to power a 290x overclocked with watercooling, the wattage ive read can peak at 300 watts during gaming, would it be fine to use or would it be safer To Get a higher rated PSU.

 

[jimthenagual]

Calculators are only to be used as a rough estimate, but this is a pretty good one. Also allows you to input your water cooling loop, as well as overclock information to calculate watts.

http://www.extreme.outervision.com/psucalculatorlite.jsp

Your PSU is more than enough to power an overclocked system with a 290x and water pumps etc.

 

[Dark Lord of Tech]

It's not a high quality supply , I wouldn't overclock with it , it's made by HEC.

In general loose voltage regulation
3.3V failed in the second Advanced Transient Response test
The unit is not rated for 50°C continuous power output but thankfully it has OTP to save it from dangerous high operating temperatures
Equipped with short cables. Also I would like to see two-three more SATA connectors and an additional EPS one
Power distribution could be better
The max combined power of the minor rails is overrated

http://www.techpowerup.com/reviews/beQuiet/PurePower_L8_730W/9.html

 

[InvalidError]

Can Anyone Explain too why the Sticker shows 730watt PSU, but adding the numbers above i get closer too 830w?

The two 12V rails are rated 30A maximum individually (up to 360W) but their combined rating is 660W, which is 60W short or in 55A combined. What that means is that the transformer's 12V output is designed for 55A and up to 30A can go out either over-current protection circuit.

It is roughly the same story with the 3.3V and 5V rails: about 80W on the 3.3V rail and 100W on the 5V rail but the combined total can only be 150W so you are 30W short there.

Humm... 810W, yeah, that's a bit weird.

The 730W limit must come from input-side over-current/over-power limit.

 

[leo1230]

thanks, ill probably stick with buying a GTX780 as thatt will give plenty of headroom on the 330watt per rail limit, although ive notice that its 30a per rail. do i ignore the 30a per rail and plug in a cable with 6 +8 pin connection on it into the gpu or show i use both cables, 1 for 8 pin and one for 6 pin so i get the full amount of current?

thanks for the help by the way, been confusing me for days.