How do I determine what size power supply I need...

[purplehayes]

How do you determine the size of a power supply that a new or exisiting computer will need?

Is there a list of the wattages that each device uses? What about a buffer zone, as in not pushing your power supply too hard?

I'm sure this is pretty straight forward, I just don't know the answer.

Thanks in advance.

PH

 

[Shagga]

The correct way I suppose is to count up all the power each peripheral etc your gunna use and then come up with an answer. The other way is to say, you need a minimum of 300W PSU as this will surfice for most ppl. The chances are this is becomming a standard requirement. Mind you if the Voodoo6 had come out you'd need a direct power source and ring main from your comsumer unit in ya house.

 

[airfoil]

A 300 watt PS is what you need. If you're going to have many peripheral devices, get a 350 watt PS, but its most likely going to be unlikely.

 

[DaddyG]

Its actaully fairly difficult to 'calculate' your requirements. The total wattage listed on a PS is pretty meaningless. The total consists mainly of +5, +3.3 and +12. Many larger supplies have lots of current available on the +12v line. Unless you have a bunch of case fans, or a peltier, this is pretty much wasted. The critical values for AMD systems are the combined total of trhe +3.3v and the +5v. You can not just add up the individual rating to get this value. the 3.3v and 5v have individual ratings BUT since they are generated by the same part of the power supply, the combined rating is less than the total of the individual. Look for a supply with a combined +3.3 and +5 of 145watts or better.

 

[purplehayes]

DaddyG Thanks!

PH

 

[RossGr]

DaddyG, HDs and CD drives as well as the fans use the 12V line so the more drives you have the more current you will need on the 12V line.

Each device lists the voltage and current rating. Power is the product (multply) of Voltage and current. Add up the power requirement for each device then add 20% to get an idea of the minimum PS you should get.

300Ws is generally safe, it is better to have execess capasicity.

 

[Shockwave]

I'm running
800 TBird @ 950
128 RAM
1 IBM 30 gig 75GXP
1 Toshiba DVD drive
1 Creative 52x CD drive
1 SCSI Plextor 8220
network card
ATI Radeon 32 DDR
SB X-Gamer 5.1
Adaptec SCSI card (obviously)

all on a 250 W power supply. Granted, I'm out of power plugs on the power supply, which is why I have another PS sitting on the floor running my other HD, so I NEED a bigger one, but dont beleive this crap that you shoudl ALWAYS get at least a 300, or if you are gonna run lots of stuff get a 350. Get a good quality name brand certified-for-your-cpu power supply that has enough plugs to run the devices in your system and you should be just fine.

 

[RossGr]

Here is another nice bit of info.

According to the AGP spec the most a AGP card can draw through the Mobo is 25W, this can be on either of the 3.3V or 12V lines or a combination of the 2. So call your AGP card 25W this will cover anything you can plug into it.

There is allowance for 110W in the AGP pro50 spec but most will be supplied through a seperate connector.

AGP spec page