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Choosing the right PSU

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December 13, 2009 10:12:22 AM

Hi, I've been looking around for several hours to learn about psu and their rails however i'm still not clear about certain things. I'm not that great with computers and just learning it bit by bit.

So far right now heres what I got for my PC, I bought it second/h so i may not be 100% accurate but:

CPU: q9400
Mobo: Gigabyte GA-EP31-DS3L
Casing: Cooler master elite
current Power supply: Cooler master 420w
HDD: Western digital 60gb
2nd HDD :500gb seagate (to be connected)
Graphics: HIS 4350

I'm currently wanting to purchase this 4890
http://www.oczone.co.nz/product_info.php?cPath=40&produ...

Now I've been reading around trying to sort out the right PSU for this, and I know everyone recommends the 550w. But how do i get more accurate measurements? And whats with the rails with different amperes? i thought there are only 3 kinds of connectors? what are they on about?

really confused here.

otherwise I'm looking to purchase this psu http://www.oczone.co.nz/product_info.php?products_id=34...

I stumbled upon this thread http://www.overclock.net/power-supplies/463947-how-sele...

and tried his formula for my comp and (with hd4890 wattage at 190 max which specs i found on another site)my comp comes out with some over 40amps per rail but i go here to check out the psu specs http://www.extremeoverclocking.com/reviews/cases/Cooler...

which shows the 12v rail doesnt go past 20A. and I still dont know whats the deal with the rails. Maybe i need to recalculate?

say i maxed everything out (some of wattage follows that psu site i found)

lets see i've got
q9400 - 95w
mobo - 40w
2 x hdd - 40w
dvd drive - 20w
fans- 4w
4890 -190w

thats total 389w have it a 70% max wattage of powersupply that would meant i have to have a psu of 505.7w. then onto the rails.... thats 505.7 / 12v = 42a

389 /12v still comes to a 32a? still way past the 20a per 12v rail

Did i do that right? or am i totally off track? Do i need bigger wattage psu??? Even if i got it right does this PSU actually will fit my cooler master atx casing??

Sorry for this entirely noob tread but how else could i learn?

So after some 7+ hours for searching i'm still back to square one :heink:  . So please help me out here.

So, well my question is fragments of everything really but the most important is that which PSU should I get?
and (apart from pulling out the multimeter) how do i more accurately get the right psu for my comp or ANY comp.

Thanks heaps




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a c 248 ) Power supply
December 13, 2009 10:57:52 AM

An atx power supply will fit in an atx pc case. No problem there.

A power supply will come with a variety of power cables with different connectors. They are standard atx connectors designed to supply power to a variety of pc components. Different components have different power requirements. Due to their unique design and shape it is almost impossible to plug the wrong power cable into a pc component.

The different rails supply power of varying voltage to components. Not all components require the same voltage. The +12 volt rail(s) supplies about 75% of the power that a modern pc uses, The two components that use the most power supplied by the +12 volt rail(s) are the CPU and the viceo card(s).

Power supply calculators are only a recommendation much like the recommendations made by video card manufacturers. They are only a rough approximation of power requirements. The results are typically overestimated because there are users who insist on buying low budget power supplies of questionable performance and value.

The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the +12 volt rail(s) can easily power a system with any single video card made. A high quality 700 to 750 watt power supply with sufficient current (amps) on the +12 volt rail(s) can power a system with two video cards operating in dual mode. There are a few exceptions like the new ATI Radeon HD 5XXX series cards which use less power due to their energy efficiency.

A high quality 500 to 550 watt psu will have a +12 volt rail rated at 40 amps. A high quality 700 to 750 watt psu will have a +12 volt rail rated at 60 amps.

In addition the power supply should be at least 80+ Bronze certified for energy efficiency. There are some models available which have achieved 80+ Silver and 80+ Gold Certifications.

Before purchasing a new psu you will need to decide whether you will eventually have a pc with one or two video cards.

Let's take a look at the official ATI Radeon™ HD 4890 System Requirements:

PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard

500 Watt or greater power supply with two 75 watt, 6-pin, PCI Express® power connectors

600 Watt or greater power supply with two, 75 watt, 6-pin PCI Express® power connectors for ATI CrossFireX™ technology in dual mode

That's for an entire system.

The Cooler Master eXtreme Power Plus 550W you are considering is adequate for your system. It is not a stellar performer but it is adequate. However, there is a problem that was pointed out in several technical reviews. It only comes with one 75 watt, 6 pin, PCI Express® power connector. The ATI Radeon HD 4890 requires two power connectors.

Corsair, PC Power & Cooling, and Seasonic are some of the brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty. Some of the newer models come with a 7 year warranty. Lately we've been seeing a few other brands offering some high quality units. An example would be the Antec Earthwatts series which is a major improvement over Antec’s older psu’s like the Basiq models.

The Corsair VX550 power supply would be appropriate for your system. It has a single large +12 volt rail rated at 41 amps and two 75 watt, 6 pin, PCI Express® power connectors:

http://www.oczone.co.nz/product_info.php?cPath=38&produ...

An alternative would be the Antec Earthwatts EA500 power supply:

http://www.oczone.co.nz/product_info.php?cPath=38&produ...

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December 14, 2009 6:59:58 AM

Awesome reply, really cleared up so much.

So are rails the connectors from the PSU to mobo?

Really awesome report, you saved my behind from buying cooler master 550w i'll be really pissed off to find that i end up with just one 75 watt 6pin when i needed two.

i'm reading the review on newegg on te 550 cosair "Like the 41 Ampere +12V rail (and there's just the one +12V rail, so you don't have to balance your power needs by hand.). "

do i need to balance power needs with other psu?

Thanks heaps again Jhonny i see you've been replying to many a threads. great job.

In the end i'll go ahead with the corsair.
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December 14, 2009 5:38:34 PM

also is there difference between micro atx and atx casing? different psu for each? thanks
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December 15, 2009 7:49:50 PM

Quote:
The Cooler Master eXtreme Power Plus 550W you are considering is adequate for your system. It is not a stellar performer but it is adequate. However, there is a problem that was pointed out in several technical reviews. It only comes with one 75 watt, 6 pin, PCI Express® power connector. The ATI Radeon HD 4890 requires two power connectors.


You are wrong, it has two 6+2Pin PCI-e Connector.
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a c 248 ) Power supply
December 15, 2009 8:41:20 PM

cristianm21 - Thank you for the information. You are correct.

I think I got the specifications mixed up with the 420 watt power supply hardy_eb mentioned.

Muchas Gracias!
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a c 243 ) Power supply
December 15, 2009 8:45:26 PM

cristianm21 said:
Quote:
The Cooler Master eXtreme Power Plus 550W you are considering is adequate for your system. It is not a stellar performer but it is adequate. However, there is a problem that was pointed out in several technical reviews. It only comes with one 75 watt, 6 pin, PCI Express® power connector. The ATI Radeon HD 4890 requires two power connectors.


You are wrong, it has two 6+2Pin PCI-e Connector.

So he was.
Real tactful way for a first time poster to let him know.
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