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Really dumb question about power supplies

Last response: in Components
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June 21, 2012 3:01:30 AM

sorry i feel like this is really stupid so work with me. I'm working on getting parts for a low power htpc. I was planning on buying a 200W itx compatible psu, but the ones with decent reviews are all around 40-50 dollars.

what if I buy a 400W PSU, but still use the same components in the build. will the PSU use up the same amount of energy as the 200W since the plugged in equipment would be the same, or do the higher watt psu's always use significantly more power?

I ask because quality 400W'ish PSU's are easily available on sale for 25-30 dollars which is half the price of the ITX ones (albeit at a larger physical size)

thanks!

btw parts if you need to know:

core i3 2125 with onboard graphics (no gpu)
mini itx motherboard (most likely gigabyte H67N unless they release an update very soon and assuming i can find it somewhere)
8gb DDR3 ram, brand/speed TBD.
120gb OCZ vertex 3 SSD (just bought it for 70 dollars, woot!)

that's pretty much it.
a c 144 ) Power supply
June 21, 2012 3:54:08 AM

Other than a small amount of power lost through inductive and capacitive reactance, a power supply will only consume the power required by the load demanded on it. In other words, no matter how 'large' a PSU you buy, it will only use the wattage your system requires. Think of wattage as being like horsepower.
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a b ) Power supply
June 21, 2012 3:58:14 AM

Well your components will draw a certain amount of power, and just because a psu is bigger it does not mean it will draw more power from the wall. It depends on efficiency. For example a 200watt psu that has an efficiency of 75% will use more power than a 500watt psu with an efficiency of 85%, so in this case the 500watt psu will be more efficient, and will provide you wit more power if needed. You can get a normal ATX psu instead and still draw less power.
Efficiency is what matters here, and it means how much of the power drawn from the wall is successfully being converted into power for your computer. so if a power supply has an efficiency of 80% then 20% is lost as heat. So lets say you have a 1000watt psu and it has an efficiency of 80%, then if you were to run it with components that would draw 1000watts total, then you would effectively be drawing 1200watts from the wall socket, as the power supply would provide its rated 1000watts, and since it is 80% efficient 20% would be lost as heat so it would draw 1200watts to provide 1000watts to your pc. I hope that was not too confusing.

PSU's are categorized into a couple of efficiency categories:

80 Plus
80 Bronze
80 Silver
80 Gold
80 Platinum
The specific efficiency for each of the ratings can be found here: http://www.plugloadsolutions.com/80PlusPowerSupplies.as...

However any powersupply that is less than 80% efficient is not certified as 80 plus. So the higher the rating the more efficient a power supply is, and the less power it will draw for the given load.

So when choosing a psu look at its efficiency rating, and just because it is larger like 600watts means that it can provide more power then say a 300watt psu, but it can also be more efficient, so if your components draw 200 watts then the 600watt psu will still draw less power.

Hope this helps, and if you don't understand something then just ask.
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Anonymous
a b ) Power supply
June 21, 2012 4:00:21 AM

though each power supply will generate that same amount of power, getting too large of a PSU will draw more power from the wall than a smaller one since efficiency takes a large nose dive under 20% load.
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a b ) Power supply
June 21, 2012 4:05:09 AM

Yes that is true, efficiency is a variable not a constant it changes with the amount of load on the psu, but I assume that your not getting a huge psu.
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June 21, 2012 4:12:55 PM

thank you all very much for the feedback it is much appreciated. On a side note, I didnt realize there were so many variations within the 80 PLUS ratings lol. your thoughts on this
CORSAIR Builder Series CX430? currently on sale at newegg for 35 dollars after rebate :) 

EDIT:
if it helps for comparison sake, the original PSU I planned on getting is this:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

its 20 dollars more and has about 200 less wattage. I'm thinking if I dont waste too much energy, then at least the corsair will give me future upgradeability.
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June 21, 2012 4:58:04 PM

That fsp is 10 times better than the Corsair CX series.
Most corsaid are made by seasonic but not the cx series. spend the money and getthe fsp. Remember its not just about power and wattage. Its about quility
if the psu goes, a cheap one will take the system with it.
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a b ) Power supply
June 21, 2012 5:15:36 PM

The CX430 would be fine for your system - and buying Corsair wouldnt exactly be playing it risky.

Though if you want to drop a little extra cash, the other one you linked would be fine too.
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Anonymous
a b ) Power supply
June 21, 2012 5:39:29 PM

redzoneos said:
thank you all very much for the feedback it is much appreciated. On a side note, I didnt realize there were so many variations within the 80 PLUS ratings lol. your thoughts on this
CORSAIR Builder Series CX430? currently on sale at newegg for 35 dollars after rebate :) 

EDIT:
if it helps for comparison sake, the original PSU I planned on getting is this:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

its 20 dollars more and has about 200 less wattage. I'm thinking if I dont waste too much energy, then at least the corsair will give me future upgradeability.


i do not think this is about the quality of a PSU but getting one that is appropriate sized. as i stated before; PSU efficiency takes a huge nosedive under 20%. i have read that many "trip out" when there is less than a 15% load but i do not know that to be confirmed.

as wise as it would be to consider future upgrading when looking for an appropriate PSU, i do not believe you rig AS IS NOW will draw 86 watts idle (20% of 430 watts). what i would highly recommend that you do when getting the corsair PSU that you do not let your rig sit idle for days with the PSU getting hot and wasting electric sitting there doing nothing.

thank you for your attention. :) 
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June 21, 2012 8:37:35 PM

ok ok i've taken everything you guys have suggested and come up with a compromise. http://www.newegg.com/Product/Product.aspx?Item=N82E168...

enough wattage to be able to add a low end graphics card if i ever need discrete graphics, 80+certified, costs only 5 dollars more then the corsair while not having to deal with rebates :) 
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a c 144 ) Power supply
June 21, 2012 9:17:52 PM

Anonymous said:
PSU efficiency takes a huge nosedive under 20%. i have read that many "trip out" when there is less than a 15% load but i do not know that to be confirmed.


I gotta ask you man, where the heck did you read that? Please pass that one on so I can read it too.
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Anonymous
a b ) Power supply
June 21, 2012 10:12:19 PM

clutchc said:
I gotta ask you man, where the heck did you read that? Please pass that one on so I can read it too.

http://en.wikipedia.org/wiki/Computer_power_supply#Effi...

the under 15% "trip" is not in the third paragraph anymore. and yes i know wikipedia is not always accurate.

i'll look for the other sources - man i have to go through a lot of bookmarks . . . :lol: 
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a b ) Power supply
June 21, 2012 10:19:13 PM

Oooo referencing Wikipedia - an intellectual faux pas! haha
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Anonymous
a b ) Power supply
June 21, 2012 10:24:26 PM

Gallarian said:
Oooo referencing Wikipedia - an intellectual faux pas! haha

fuax pas?

i aint skeerd. i have used my tie for a napkin before ya know.
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a c 243 ) Power supply
June 21, 2012 10:36:29 PM

redzoneos said:
ok ok i've taken everything you guys have suggested and come up with a compromise. http://www.newegg.com/Product/Product.aspx?Item=N82E168...

enough wattage to be able to add a low end graphics card if i ever need discrete graphics, 80+certified, costs only 5 dollars more then the corsair while not having to deal with rebates :) 

You've mentioned ITX, ATX, and now TFX power supplies but nothing about your case, that's going to determine which form of psu you'll need
If TFX is what you will need spend the extra $5 and get a Seasonic
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

ATX for the same price
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
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a c 144 ) Power supply
June 21, 2012 11:02:01 PM

Anonymous said:
http://en.wikipedia.org/wiki/Computer_power_supply#Effi...

the under 15% "trip" is not in the third paragraph anymore. and yes i know wikipedia is not always accurate.

i'll look for the other sources - man i have to go through a lot of bookmarks . . . :lol: 

Yeah, I can see why that would have been removed. Everyone's computer would shut down when idling.
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Anonymous
a b ) Power supply
June 21, 2012 11:47:40 PM

clutchc said:
Yeah, I can see why that would have been removed. Everyone's computer would shut down when idling.

not necessarily . . . and that's a pretty sweeping generalization. :non: 
only problem is it linked to citation i used for a reference point that i didn't bookmark. :p 
my point being illustrated:

Debunking Power Supply Myths
now of course you can point out it is an older article . . though if everyone's system idles @ less than 15% of their PSU . .what a waste!
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a c 144 ) Power supply
June 22, 2012 12:30:14 AM

Anonymous said:
that's a pretty sweeping generalization. . . though if everyone's system idles @ less than 15% of their PSU . .what a waste!

Sweeping generalization?
I realize we are getting a bit off the OP's original question. And I don't mean to perpetuate an argument. But the PSU in my sig below is idling at 109W as we speak. That's less than 13% of its rated wattage. Are you saying that is some kind of a waste because it is running below 20% of its rated capability? I'm not going to use a lesser PSU just so my idle wattage remains above 20%. And it certainly never 'trips out' due to it running below 20% of its capability.
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Anonymous
a b ) Power supply
June 22, 2012 1:07:24 AM

clutchc said:
Sweeping generalization?
I realize we are getting a bit off the OP's original question. And I don't mean to perpetuate an argument. But the PSU in my sig below is idling at 109W as we speak. That's less than 13% of its rated wattage. Are you saying that is some kind of a waste because it is running below 20% of its rated capability? I'm not going to use a lesser PSU just so my idle wattage remains above 20%. And it certainly never 'trips out' due to it running below 20% of its capability.

1) excuse for taking a word such as everyone'sas a sweeping generational.
2) yes, if your system idles @ less than 15% or 20% you are being wasteful.
Quote:
Generally you want your idle power draw to fall into ~30%-40% of the PSU's rated wattage, and your peak power draw to fall into ~70%-80% of the PSU's rated wattage.

have another citation though i don't think you are bothering with any.
On Efficiency
3) i did not elude to:
Quote:
And it certainly never 'trips out' due to it running below 20% of its capability.

i said:
Quote:
i have read that many "trip out" when there is less than a 15% load but i do not know that to be confirmed.

now first of all where is there stated EVERY? i believe MANY is the word there. i also stated that it was not confirmed; meaning take it with a grain of salt.
4) for someone who doesn't mean to perpetuate an arguement; why post an adversarial reply?

i am not looking for a debate, i just simply stand by what i posted; if the OP wants to get a 430 watt PSU it would be prudent to not let it idle for long because the PSU would not be running efficiently. if your practice is to go overkill on a PSU, that's on you.
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a c 144 ) Power supply
June 22, 2012 3:19:38 PM

Anonymous said:

4) for someone who doesn't mean to perpetuate an arguement; why post an adversarial reply?

You're right. Why would I want to continue this discussion with you? I quit.
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June 22, 2012 10:11:51 PM

delluser1 said:
You've mentioned ITX, ATX, and now TFX power supplies but nothing about your case, that's going to determine which form of psu you'll need
If TFX is what you will need spend the extra $5 and get a Seasonic
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

ATX for the same price
http://www.newegg.com/Product/Product.aspx?Item=N82E168...



I didnt mention any cases because i'm going to be putting this build inside one of my home theater desk drawers (another thread). Form factor of the PSU won't matter at all, I can work around it, though smaller sizes would be more ideal.

those Seasonics look good thanks for the links :) 

@ everyone else, really appreciate all the feedback and suggestions thank you!
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