PSU's explained

[xirokx]

Hi Peeps,

Can someone please educate me with regards to PSU's...

I need a new one and I know there are:-

- modular psu
- atx psus

I currently have an Antec PSU, and its great, I can plug or unplug PCI and Molex cables into the actual PSU, does that mean its modular?

Also when purchasing a PSU, whats all this rails stuff? If I want it to last and to be confident it will power my RIG then whats are the musts and flaws to avoid?

All help and advice would be appreciated.

Thanks

 

[decto]

If you can disconnect leads from your PSU then it is modular. The main purpose of this is to allow a number of options of different types of connections without having to hide a lot of cables away.

The rails are quite simple.
If a PSU has 3 +12V outputs of 18A each it is said to have 3 12V rails

A rail is an independant output of a voltage.

These will be split accross the different connectors with the aim of spreading the load so no single output (rail) is overloaded. I.e. the PCI-E card will be supplied from a different output to the CPU. For some older and cheaper designs this can be an issue as it is possible to overload part of the supply by using adapters to connect the load in an atypical manner. Eg. trying to add a second high end VGA card.
To complicate things further, some PSU's state individual outputs but are really single rail units.... blame marketing. Corsair HX 520/620 does this and then claim to 'load share'. There is nothing wrong with that way of working.. they are good PSUs ... just a little more to confuse.

Power units are now moving back to a single high capacity output to avoid this so would be listed as : +12V 50A

The key thing with a modern PSU is the current available at +12V since this is where most of the power is required.

+12V 50A = 600W ... you simply multiply them.

Some PSU have high current outputs available on +5V and +3.3V which they choose to count towards the total output. In these cases 600W is not always the same as 200W of that could come from the lower voltages leaving you only 400W ~ 33A at +12V

Buy on brand, 12V output and the right mix of connectors / modular.

AD

Edit: As a guide. Expect to pay £12 -£15 per 100W output when buying online (since the big retail stores have a silly markup). If you are paying much less..... ask why!

 

[gareth170]

I currently have an Antec PSU, and its great, I can plug or unplug PCI and Molex cables into the actual PSU, does that mean its modular?

yep

Also when purchasing a PSU, whats all this rails stuff? If I want it to last and to be confident it will power my RIG then whats are the musts and flaws to avoid?

multi 12v rails means basicly if the psu as 4 12v rails there'll be a rail for the motherboard & cpu, another rail or 2 for gpus, and another rail for other hardware like hdd's, dvd drives, fans.

 

[xirokx]

great thanks guys, can you get modular psus with the new 8 pin connector - i forget the proper term but its the additional connector for new skt 775 mobos??

 

[gareth170]

great thanks guys, can you get modular psus with the new 8 pin connector - i forget the proper term but its the additional connector for new skt 775 mobos??

yep.

even my £69 psu modular as a 8 pin connector. it's cheap but works perfect, . had it for over 11 months without problems.

 

[Tetras]

great thanks guys, can you get modular psus with the new 8 pin connector - i forget the proper term but its the additional connector for new skt 775 mobos??

8 pin motherboard connector is part of EPS12v spec (along with 24 pin connector) and present on pretty much all ATX 2.x PSUs.

The 4/8 pin won't (usually) be a modular cable.

Just to clarify with the +12v rails, the overall rating is not (reliably) all rails added together, it is the "max combined wattage" (this figure tends to be openly stated by good manufacturers and hidden by dodgy ones).

Also note that output depends on build quality, poor PSUs won't provide stated power at a realistic temperature but good PSUs will do this up to and beyond 50c (though I wouldn't run any PSU long-term 100% load at 50c ambient unless you like RMAs).

 

[xirokx]

thanks...

can u spec me a bang for buck modular psu in that case then??

are modular psus the best of them or is there better??

also whats an atx psu?? are all psus atx?? or do u get other types aswell??

 

[gareth170]

thanks...

can u spec me a bang for buck modular psu in that case then??

are modular psus the best of them or is there better??

also whats an atx psu?? are all psus atx?? or do u get other types aswell??

http://www.overclockers.co.uk/showproduct.php?prodid=CA-005-CS&groupid=701&catid=123&subcat=1084

or

non modular http://www.overclockers.co.uk/showproduct.php?prodid=CA-008-CS&groupid=701&catid=123&subcat=1084

modular just means u can disconnect the cables from the psu.

 

[Tetras]

are modular psus the best of them or is there better??

As a general rule modular PSUs aren't better or worse than non-modular. If you don't need the modular feature (because you can hide the cables in the optical bays/elsewhere, don't care about unused wires or will use all the cables provided anyway) then get a non-modular PSU (they are often cheaper too).

also whats an atx psu?? are all psus atx?? or do u get other types aswell??

ATX is the standard format for PSUs and cases, for PSUs it is updated every so often and is up to 2.2 I believe.

If you are mad enough to read the entire specs then go here:
http://www.formfactors.org/formfactor.asp

If I recall correctly ATX 1.3 added the 4 pin +12v connector for Pentium 4s, ATX 2.0 added 24 pin connectors (from 20). Most boards and PSUs (power connector wise) use 24 pin block and 4 or 8 pin blocks for the motherboard. If a PSU has a 24 pin and 8 pin connector it is said to be "EPS12v compliant".

There are other PSU formats, Antec just released a new one purely for Antec products and there are small form factor (SFF) PSUs and Pico-PSUs but what you buy on the shelf will almost always be ATX (it'll say on the box anyhow).

Edit: I didn't recall correctly, 1.3 added optional SATA connectors.

 

[xirokx]

thanks peeps...