How can I accurately estimate my power needs?

[legocitytruck]

I am building a new machine and I have an old 420W power supply lying around. I am trying to decide if I need to buy a new power supply. How do I determine how much power my new components will need and if my old supply can handle it?

 

[Gillbot]

Why risk new parts on an old power supply if you are unsure? It's cheap insurance to buy a newer quality power supply to suit your new build.
Otherwise: http://www.antec.outervision.com/

 

[legocitytruck]

Hmmm, good point.

Is this a good choice? :

http://www.newegg.com/Product/...x?Item=N82E16817341010

 

[HOOfan 1]

Originally posted by: legocitytruck
Hmmm, good point.

Is this a good choice? :

http://www.newegg.com/Product/...x?Item=N82E16817341010

It is OK, what are you planning to run

 

[magreen]

Tell us exactly what your new rig is, and just for the heckuvit tell us exactly what your old 420w psu is. That way we can make fun of it :evil:

 

[legocitytruck]

The new system is:

Memory: 4GB DDR2 800 on two sticks
CPU: AMD Phenom 8450 Toliman 2.1GHz Socket AM2+ 95W Triple-Core Processor Model Mobo:GIGABYTE GA-MA780G-UD3H AM2+/AM2 AMD 780G HDMI ATX AMD Motherboard - Retail
Video card:may upgrade to a non-intergrated card later
Network card
Extras:
Floppy drive
DVD drive
DVD-RW drive
3 or 4 case fans

I may upgrade to a Phenom II at a later date

What are the best features to look for in a power supply?

 

[Yellowbeard]

Originally posted by: legocitytruck
What are the best features to look for in a power supply?

Read the first 7 posts in this PSU section which are sticky posts about PSUs.

Also, the main things you need to consider are your 2 most power hungry components, the CPU and the GPU and their 12v demands. Check the power consumption on whatever products you are going to buy and then figure in other factors like HDs.

 

[magreen]

Legocity: your new system's power consumption will be miniscule. Even if you add a discrete video card later, it still wouldn't consume much power unless you add a monster of a card.

You didn't tell us what your old 420w psu is. It may be ok to keep it for your new system if it's of high quality.

 

[legocitytruck]

Sorry, my old 450 (not 420 - typo) Power supply is a NSpire Power Supply NSP-450P4DL ATX1.3 (12V:25A) 450W 2 B.Bearing

I can't seem to find any specs on it and if it has an internal LED, it does not work.

 

[magreen]

Originally posted by: legocitytruck
Sorry, my old 450 (not 420 - typo) Power supply is a NSpire Power Supply NSP-450P4DL ATX1.3 (12V:25A) 450W 2 B.Bearing

I can't seem to find any specs on it and if it has an internal LED, it does not work.

The brand of your old psu doesn't inspire a lot of confidence in me. It's not one of the oldies but goodies AFAIK.
1) it may have never been able to deliver its claimed output of 450W (especially at the temperatures it actually runs at inside a case, as opposed to 25C that they rate a lot of the cheapo psus at). Lots of the cheapo psus can actually only reliably deliver 50% or less of their rated maximum.
2) it's the old 1.3 spec meaning its power won't be distributed to mostly the 12V rail as modern systems demand
3) it may have noisy output that drifts out of spec, which can damage equipment over time.
4) it's not new, which means it's probably deteriorated over time.

On the other hand, your system as you have it now will draw about 100-150W at full load. It's not even going to load your psu to 30% of its 450W rated capacity. As long as you don't add a discrete graphics card that requires its own 6- or 8-pin pci-e power connector, you'll be pulling way less than your psu claims to be able to handle.

So it's your decision. You could play it safe and get a new quality psu. You don't need a lot of power. Look around on the hot deals section -- there was a corsair 400w for $30 w/ free shipping a few days ago that just went out of stock. This is probably the wiser course of action.

Or you could try it with the old psu, knowing that it would probably work fine but that there are risks involved.

 

[legocitytruck]

magreen: thank you for your skilled recap.

I am glad to learn that I can use a lower powered psu, which means lower cost, and means I will follow your advice and purchase a new one.

Other than the new 12V rail design, what other features are a must for reliability in a 400W psu? If it means anything, the machine will be running nearly constantly.

 

[magreen]

Originally posted by: legocitytruck
magreen: thank you for your skilled recap.

I am glad to learn that I can use a lower powered psu, which means lower cost, and means I will follow your advice and purchase a new one.

Other than the new 12V rail design, what other features are a must for reliability in a 400W psu? If it means anything, the machine will be running nearly constantly.

That's the thing. It's not really features you need for reliability, but quality.

Look for these brands: Corsair, BFG, pc power & cooling, seasonic, silverstone, Antec (earthwatts line; Basiq is ok too). When you find a model, search for reviews of it on Anandtech.com, jonnyguru.com and hardocp.com.

The features that will matter to you are 80+ efficiency certification, APFC, probably a 120mm fan since it's usually quieter, and a 6-pin power connector in case you want a more powerful graphics card in the future.

 

[legocitytruck]

Wow, thank you for the amazing information magreen! When searching for a psu, is it generally better to purchase one with three 12V rails vs. one or two?

 

[magreen]

Originally posted by: legocitytruck
Wow, thank you for the amazing information magreen! When searching for a psu, is it generally better to purchase one with three 12V rails vs. one or two?

My pleasure. With modern psus it makes no difference how many rails it has. Just what the total combined 12V power rating is (i.e. not just the individual 12V ratings added together), and if the company is trustworthy in delivering what they claim.