What's the real story on Power Supplys?

[aidanjt]

All told you'll be looking to spend around £40-50 anything over that is going to be over kill. (if you don't overclock, it's overclocking that the PSU stability start to become a major major issue)

I'm sorry, but that's just plain wrong. PSU stability is a constant factor, overclocking or not, overclocking simply draws more current, it doesn't add an extra dimension to electrical physics or anything.

[Pob255]

I'm sorry, but that's just plain wrong. PSU stability is a constant factor, overclocking or not, overclocking simply draws more current, it doesn't add an extra dimension to electrical physics or anything.

And that's my point, when you start to overclock and pust the limits tolerances become tighter and weaknesses start to show.
The reason we can overclock in the first place is that much of the stuff we use can be pushed thurver but is scaled back for stock settings to give better tolerances and a greater working life.


Back to the topic

Do you have a max budget? If not then set one and go for the best you can within the price range.

Great advice, I fully agree.

[aidanjt]

And that's my point, when you start to overclock and pust the limits tolerances become tighter and weaknesses start to show.
The reason we can overclock in the first place is that much of the stuff we use can be pushed thurver but is scaled back for stock settings to give better tolerances and a greater working life.

Yes, but, if you have a 380W PSU with a 18A +12V rail, and you only draw 10A normally, then drawing another 4A doesn't change anything.

[fat jez]

Yes, but, if you have a 380W PSU with a 18A +12V rail, and you only draw 10A normally, then drawing another 4A doesn't change anything.

Actually, that's not true. As you draw more current, the heat increases (P=I^2R), which in turn, alters the characteristics of the components in the power supply. So that extra 4 amps almost doubles the amount of heat the power supply is putting out.

Cheers,
Stephen

[aidanjt]

Actually, that's not true. As you draw more current, the heat increases (P=I^2R), which in turn, alters the characteristics of the components in the power supply. So that extra 4 amps almost doubles the amount of heat the power supply is putting out.

Cheers,
Stephen

That depends highly on the transformer involved, and division of current, 4A doesn't mean double the heat by drawing extra current from the 12V rail, remember power consumption is in proportion of voltage *and* current, 4A on the 12V rail doesn't mean 4A from the mains (@220-240V).

[fat jez]

That depends highly on the transformer involved, and division of current, 4A doesn't mean double the heat by drawing extra current from the 12V rail, remember power consumption is in proportion of voltage *and* current, 4A on the 12V rail doesn't mean 4A from the mains (@220-240V).

OK, if for the sake of simplicity, we assume that the PSU has a resistance of 1 Ohm. Your 10A means the power being dissipated through your resistance is 100W. Now crank that current up to 14A and you are talking 196W, or nearly double. Now those figures are plucked out of the air, as I doubt the resistance of the transformer is that high, but that fact remains that resistance does change with respect to temperature.

Higher spec components found in a decent PSU will not vary as much as lower ones, so you really want to have a comfortable margin before you hit the limits of the PSU.

My degree is in Electronic and Electrical Engineering from the University of Strathclyde, where is yours from?

Cheers,
Stephen

[aidanjt]

Oh yes, the resistance does change in proportion with temperature, but a lower initial resistance (higher power transformation efficiency) means less heat overall even under full load. My point was initially that an extra 4A off the 12V rail is a small increase compared to the rest of the system, thus the heat would not, and cannot double, that would fly in the face of thermal dynamics.

[Blitzen]

My degree is in Electronic and Electrical Engineering from the University of Strathclyde, where is yours from?

Doesnt make you a PSU expert though does it?

[Sprite]

As a side note, is there any software I can use to check my PSU, IE ripple, max draw at load etc ?

[poindextermatic]

I've used cheap PSU's in the past and never really had a problem, the only downside I found was tht they are loud and hot, other than that they do the job. They are all built to certain standards, being British standards that's usually quite high in my experiance. Maybe I have just been lucky over the past several years... I now have a more expensive one (see sig) it's quite and cool and gives me peace of mind, and so it should for £75!

[aidanjt]

As a side note, is there any software I can use to check my PSU, IE ripple, max draw at load etc ?

No, the sensors for that are a bit too expensive to build into PSU circuits, PSU sensors are usually limited to the fan speed and temperature at best. You'd have to buy 3rd party equipment to measure that stuff with any kind of precision.

[amjedm]

As a side note, is there any software I can use to check my PSU, IE ripple, max draw at load etc ?

As advised by aidanjit you can't check with software.

If you want to check voltages then get a digital multimeter.

Edit: misread your post - Maplin and Lidl (once in a while) sell the adapters that measure wattage at the wall socket.

[Agent]

As a side note, is there any software I can use to check my PSU, IE ripple, max draw at load etc ?

No, the sensors for that are a bit too expensive to build into PSU circuits, PSU sensors are usually limited to the fan speed and temperature at best. You'd have to buy 3rd party equipment to measure that stuff with any kind of precision.

There is actually a new Gigabyte PSU that can do this - Im just trying to find a link
But as aidanjt pointed out, this is not usually the case

[Agent]

http://www.hexus.net/content/item.php?item=9057

[Craig321]

I'm going to build a new PC with a E6750 cpu, X1950XT graphics card, 2 hard drives and 2 dvd-rw drives.

In another thread, people have recommended the Corsair 520W PSU @ £70! - that seems a little overkill to me.

Ebuyer has a lot of cheap PSUs like this one for example : Extra Value 550W Gold ATX Silent PSU @ £19.98 inc VAT. It has good looking rails with 12V @ 30A and 5v @ 35A.

Then I came across this : Huntkey True 450W PSU @ £32.89 inc VAT.

In reading reviews on ebuyer, a few bad reviews of the extra value PSUs said that "it's definately not a true 550W". Then I saw this one saying it's a True 450W - So what do they mean by saying it's True?

I filled in the PSU Calculator, and it came out with only 385W with the whole system filled in.

I don't want to spend more than I need to on building my new system, so can anyone recommend a PSU?

Seriously, don't go cheap on PSU. When a cheap PSU blows it can take out EVERYTHING so you'll be spending all that money on nothing if some crap PSU blows it all up.

Corsair HX 520w = very good idea.