Beginners guide to sizing a power supply?

LittleGreyCat · 15 Sep 2016 at 15:00

There are quite a lot of posts giving a configuration and asking if a PSU will be big enough.

Is there a beginners rule of thumb to aid sizing the maximum power demand for a system?

I can see ratings for video cards, for example, but HDDs and SSDs can vary quite a bit and I have no idea which components I would need to add in the future.

Also the maximum power draw for individual components is likely to come at different times. For example on system start up the disc drives are likely to be pulling their maximum power to spin up the drives, but the video card is unlikely to be running at maximum power.

Any guidelines such as allow 25W for each HDD?
Any idea how much a motherboard draws and how much each memory stick draws?

I guess the experts have some kind of simple rule to be able to check the configurations posted here.

cheesyboy · 15 Sep 2016 at 15:10

You don't need to get too precise, to be honest.

As a broad rule of thumb, 500W is more than enough for a single-GPU system.

wakadoo · 15 Sep 2016 at 15:21

have a play here http://outervision.com/power-supply-calculator

LittleGreyCat · 15 Sep 2016 at 15:25

I have a 400W PSU.

I'm trying to work out if it will be big enough for this configuration.

My basket at Overclockers UK:

1 x Gigabyte 990X-Gaming SLI - AMD Piledriver FX-6 6300 6 Core - 8GB DDR3 Memory Bundle **£20 Saving**= £191.96
1 x MSI GeForce GT 710 SILENT "Low Profile" 2048MB GDDR3 PCI-Express Graphics Card= £29.99

Total: £232.45
(includes shipping: £10.50)

Various pessimistic assumptions have got be up to around 300W but I have no figure for the motherboard and memory. Although I have a figure for the processor I have no idea if it includes the stock cooling fan.

I am assuming 6 * HDD at 25W peak power each, 4 case fans at 10W each.

I will no doubt need some headroom for attached devices drawing power from USB.

So - below your guideline of 500W.

Ace Modder · 15 Sep 2016 at 16:44

I think the 500w guide is more for a gaming grade GPU system. Your selected GPU needs very little power to run.

A gaming GPU (£300+ GPU) can use 200w of power on it's own at peak. Realistically for most applications will be slightly under.

pastymuncher · 15 Sep 2016 at 19:42

Which psu do you have (make and model)? Not all psu's are created equal and I have seen so called 500w psu's with only 200w on the 12v rail where it's actually needed. A lot of them would probably have blown up before they even got to their pathetically weak limits as well. Always buy a quality branded psu and even then only after you have done some research to see if it's actually any good.

I hope you are not intending to do any gaming on that lot because the gpu that you have selected is not a gaming card. What will the pc be used for? Please tell me you are not swapping from a 2500k to that FX6300 because it will be a downgrade?

Gze · 15 Sep 2016 at 21:15

If I remember this is your power supply?

http://www.silentpcreview.com/Corsair_CX400W

The wattage should be more than enough considering the GPU chosen barely uses much power. However, you said you wanted 6 HDDs but the power supply only has 3 SATA power connectors. If you wanted to power 6 HDDs you may need to get adaptors to turn some of the 4 pin molex connectors into SATA ones.

Motherboard, RAM, Fans don't consume too much power. 400W should be enough and consider that not everything will be at maximum load all the time.