5 replies to this topic

[TheLegendOfMart]

Just sold an AMD 7850 to a mate who wants to crossfire it but he only has 530W PSU, BeQuiet Purepower L7, its advertised as Crossfire capable and its an 80 PLUS effecient PSU.

His Spec:

Core i5 2400 (not overclocked) - 60W Full Load
2Gb 7850 - 130W Full Load, x2 260W
2x SATA2 Rotating Media HDD - 10W each, so 20W
SSD - 5W

So we are looking at 345W not including, mobo, ram, optical drive, USB devices. With all that it cant be more than 450W surely?

Would a decent 530W PSU be enough for the above spec?

[theyarecomingforyou]

Using the PSU calculator on the Thermaltake website and approximating the hardware specs you ommitted it comes out around 440W - you'll want to check it out yourself, as I took a Worst Case Scenario™ approach. Considering most PSUs work at best around 85% efficiency he'll be able to run a second card but really he should have a 650W to be comfortable. The AMD website recommends 600W.

[Muhammad Farrukh]

Nope. Not recommended at all.

Minimum one should be a 600W for the setup

[TheLegendOfMart]

Ok great thanks will let him know.

Just wondering why its not recommended if the worst case scenario is 440W, that leaves 90W free?

If PSUs work best at 85%, 85% of 530W is 450W which is what the full load worst case scenario is for the above spec?

[theyarecomingforyou]

Just wondering why its not recommended if the worst case scenario is 440W, that leaves 90W free?

The efficiency of the PSU dictates how much energy is wasted - that is, the amount which is converted into heat. Also, the Thermaltake website recommends adding 20% if the PSU is to be used for more than a year and that would take the wattage up to 528W. As you can see, that's clearly right on the limit. I did make sure my estimate was conservative, which is why I recommended going through the PSU calculator with the actual specs, but while such a PSU is technically capable of running Crossfire it wouldn't be recommended.

[TheLegendOfMart]

Thanks for the excellent information, will recommend he buy a better PSU as well then.