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post #1 of 28 (permalink) Old 2014-10-09, 04:54 PM Thread Starter
 
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Power Supply

I went out and bought a power supply today. Corsair CX430 is what the guy at the computer parts store recommended to go along with my EVGA GeForce GTX 650 with 1GB GDDR5 Memory. The specs on the video card state I need a 400W+ PSU with a minimum of 20A on the +12V rail. Then the astrics state minimum system requirement based on a PC configured with an intel Corei7 3.2Ghz processor. Well I have a 2.6Ghz dual core, amd am2 (am2/am2+ compatible), with 4gb DDR2 ram, 320GB 7200 RPM HD.


Specs on the Corsair CX430 ($50) are,

Output
Maximum Load
Voltage +3.3V(20A, 120W) +5V(20A, blank) +12V(28A, 336W) -12V(0.8A, 9.6W) +5Vsb (3A,15W)
Total Output 430W

Basically the guy said you look at your amps, not the total Wattage, so your +12V is your video card, +5V is your peripherals. OK Very helpful, I guess.

Now I go searching their website, and some cards have a +12V1 and +12V2, what do those mean?

EVGA 430 ($40) specs are this,
Maximum Load
Voltage +3.3V(24A, 120W) +5V(15A, 120W shared with 3.3V) +12V1(34A, 406W) -12V(0.3A, 3.6W) +5Vsb(3A, 15W)
Total Wattage 430W @ 40° C

Wouldnt the EVGA be better? Or is that a lesser brand then Corsair?

I am upgrading an old HP Pavilion from 300W.

The specs on my computer state I have a Micro ATX frame, will my PSU fit? All it says is "Designed to meet the ATX standards for cases, mothervoard and power supplies. The dimensions of the Corsair CX430 are 150mm x 86mm x 140mm.
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post #2 of 28 (permalink) Old 2014-10-09, 07:58 PM
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If I were you, I wouldn't take any of the 2. Why limit yourself at 430 when you'll need a bigger one as soon as you add something new? I would get a 550-600watt power supply. If your video card needs 400 watts, a 430 would be too close for comfort. It would probably be working overtime.

A bigger one on the other hand , would give what you need and have some spare if need be. And also run without stress. The main cause why power supplies die.

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post #3 of 28 (permalink) Old 2014-10-09, 09:40 PM
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Now I go searching their website, and some cards have a +12V1 and +12V2, what do those mean?
Some PSUs have two +12v outputs, sometimes called rails. One is usually for the CPU and the other for everything else. It can be an advantage for very high power CPUs or if a very stable +12v voltage is required.

The Corsair CX430 will be fine for this system. I've used similar Corsair PSUs with similar systems and they worked well. They are good performers at a good price. Since the original PSU was 300w, a 430 PSU is a significant upgrade.

The EVGA GeForce GTX 650 recommended PSU of 400w and a 20A rail is a worst case scenario. It assumes a high powered CPU with lots of peripherals. It may also assume a dual rail PSU, where the 12v amp rating is almost halved for each of two rails. The EVGA GeForce GTX 650 actually draws 65w max. That's only 4A on a 12v rail. You don't say which model CPU is in the system but 2.6Ghz dual core am2 CPUs typically draw about 65w max. Even at full load, this system will draw no more than 200w. I've seen more powerful systems that draw significantly less.
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post #4 of 28 (permalink) Old 2014-10-10, 01:57 PM
 
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Quote:
The specs on my computer state I have a Micro ATX frame, will my PSU fit? The dimensions of the Corsair CX430 are 150mm x 86mm x 140mm.
. From personal experience, the HP machines from then usually take the smallest ATX power supply. Check the measurements against the existing one before you start the transplant in case you need to swap it.

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post #5 of 28 (permalink) Old 2014-10-13, 08:23 PM
 
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Quote:
Originally Posted by matt4x4 View Post
Specs on the Corsair CX430 ($50) are,

Output
Maximum Load
Voltage +3.3V(20A, 120W) +5V(20A, blank) +12V(28A, 336W) -12V(0.8A, 9.6W) +5Vsb (3A,15W)
Total Output 430W

Basically the guy said you look at your amps, not the total Wattage, so your +12V is your video card, +5V is your peripherals. OK Very helpful, I guess.
Time for a little bit of Ohm's law theory...

Here is the general formula for Ohm's law: V = I x R (or V = A x R). Power is a combination of Voltage and Current, so to calculate power P (or W) = V x I (or A). Simple algebra allows one to play with the formula to solve for either value.

Based on the specs of the power supply you quoted...

+3.3V(20A, 120W) ( 3.3 x 20 = 66W actually)
+5V(20A, blank) (5 x 20 = 100W)
+12V(28A, 336W) (12 x 28 = 336W, got this one right)
-12V(0.8A, 9.6W) (12 x 0.8 = 9.6W, also right)
+5Vsb (3A,15W) (5 x 3 = 15W, right again)

So now add up all the power (Watts) = 526.6W?!? How'd they say it was a 430W supply?
Here's how they come to that number. The maximum total power available for the whole power supply is approximately 430W (most likely a bit more, I'll explain that later). When you put a load on each of those rails (or voltages), each of them collectively will draw power from the primary side of the power supply (the side where the 120VAC goes into).

Let's say the 12V rail is drawing full current, at 28A, and the 5V rail is drawing 3/4 of it's rated current at 15A. So then 12 x 28 = 336 W and 5 x 15 = 75W, so a total of 411W is being pulled out of the supply. Given that it's rated at 430W, that'll leave 19W available to be drawn by the other rails. If you tried to exceed that remaining power, the whole supply will start to "fold back" on all the rails, meaning that all the rails will drop in voltage to compensate for the extra draw.

The 430W rating is determined by the actual power rating - 10% for performance/safety reasons. It's likely the average Corsair 430W power supply is capable of supplying up to about 480W. With varying values of resistors, capacitors, inductors and transformers, as well as the diodes and voltage regulators, a 10% allowance is typical. Also, if you were to load down the power supply to 430W across the rails, you would see that you are actually drawing more than 430W from the 120VAC line. This is loss due to inefficiency of the power supply and also a loss in the heat generated. Switching power supplies (the ones usually used in PCs) are typically more efficient than standard power supplies (transformer, rectifier, filter, regulator).

Hope this helps in understanding how power supplies get their ratings. As for the 12V1 and 12V2, ExDilbert is right. The secondary side of the power transformer would have 2 coils for each of the 2 12V rails, and each would operate independently of each other, up to the maximum rating of the whole power supply.
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post #6 of 28 (permalink) Old 2014-10-14, 02:00 PM
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Quite correct but a little more info than required. The bottom line is that a PC with these specs will draw nowhere near 430W total or 20A on the 12V rail, even at full load. Between 100W and 150W would be typical (as measured by a power meter on the 120v supply.) A 430W PSU is more than adequate and Corsair makes a good PSU for the price.
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post #7 of 28 (permalink) Old 2014-10-14, 06:28 PM
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I agree with ExDilbert - many PC power supplies are way overspec'ed these days. When you operate at too low of a load the PS is less efficient. This sounds like an older PC but newer PCs, even very high end PCs, rarely draw much more than 150W especially if you use an integrated GPU and an SSD. This will be even more the case when Broadwell CPU start to make their way into the market, at least when it comes to Intel CPUs.

@Danster - The video card doesn't need 400W, the minimum system power requirement is listed at 400W which seems ridiculously high unless you have multiple Graphics cards and a ton of hard drives. The highest TDP I remember for CPUs is 130W.

@Matt - I believe in the specs for that card it also says that the card draws a maximum of 64W. You don't mention the exact model of your CPU but it seems that dual core AM2 socket CPUs that run at 2.6GHz use about 65W. Add 10W for a hard drive, 20W for memory, 10W for fans and 50W for your mobo. That adds up to 220W. Still lots of buffer room.
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post #8 of 28 (permalink) Old 2014-10-15, 06:51 PM
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@Wayne,
On my computer, I have 6 hard drives, Gtx750video card, numerous USBs connected and 2 DVD/bluray drives. I need all the power that is available. Reason I suggested a bigger PS is for future expansions. It's always easier to have more available than having to install it again later. I guess I was no use at all. Must be the only one with 16 working computers.

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post #9 of 28 (permalink) Old 2014-10-16, 12:12 PM
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Even with all that, a good 450w PSU would be adequate. The Gtx750 video card consumes 55w max and spec's a 300w PSU. 6 hard drives will not consume more than 60w, much less at idle or using energy efficient drives. Two BD drives are 20w max. USB devices will be a maximum of 5w each so even 10 will be under 50w. Add it all up, even under a worst case scenario, and it's still under 450w.

nVidia chips do not spec a larger PSU until the 760 series, at 500w. Even then, a 450w single rail PSU would suffice with the OP's system. Once the 770 series or higher GPU is reached, a larger PSU would be indicated, especially if it was combined with a very high power CPU or more than one GPU using SLI was used.
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post #10 of 28 (permalink) Old 2014-10-16, 03:56 PM
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Quote:
Originally Posted by Danster View Post
@Wayne,
On my computer, I have 6 hard drives, Gtx750video card, numerous USBs connected and 2 DVD/bluray drives. I need all the power that is available. Reason I suggested a bigger PS is for future expansions. It's always easier to have more available than having to install it again later. I guess I was no use at all. Must be the only one with 16 working computers.
Totally agree...you simply cannot have too much power.

I have a Corsair AX760 760W Modular Power Supply and although it's overkill...I would much rather never have to worry about a Power Supply again for as long as this PC lives.
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post #11 of 28 (permalink) Old 2014-10-16, 04:12 PM
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I have had basic power supplies in the past and never understood why it would sometime crash for no reason. A friend of mine highly involved in electronics asked me about how big my PS was. When I told him, under his advice, I changed it to a bigger model and suddenly, the computer behaved like a brand new one.

Maybe for the common basic user, a normal PS would do but if the Op does anything like I use my computers, he wouldn't settle for the passable.

You can ride on the highway with a 250cc motorcycle but I would rather be on a 1000 and above for the just in case mishap.

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post #12 of 28 (permalink) Old 2014-10-16, 04:39 PM
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Originally Posted by Danster View Post
You can ride on the highway with a 250cc motorcycle but I would rather be on a 1000 and above for the just in case mishap.
Yeah, but if you just want to commute to work at 0-60 kph, then that 1000 will get old quickly and use a lot more fuel. A properly sized power supply is less expensive and more efficient. Just like home HVAC, too large is not good.

My Mac Mini uses only about 40W max, so my message for the OP is to figure out an appropriately sized Power Supply for his needs.

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post #13 of 28 (permalink) Old 2014-10-16, 10:35 PM
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But 57, this is the information super highway. I just gotta have the power!

Like I mentioned, it all depends what you use your computer for. My Amiga 2000HD has a 150 watt PS and it runs like new. And yes, I still use it. My love for that OS will never die. That 60 meg scsi is just full of 90's gems.

To each his own.

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post #14 of 28 (permalink) Old 2014-10-17, 01:59 AM
 
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Originally Posted by Danster View Post
But 57, this is the information super highway. I just gotta have the power!
This line made me think of this, sorry for going off-topic...

http://www.youtube.com/watch?v=UfD9fWt8hrQ
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post #15 of 28 (permalink) Old 2014-10-17, 02:28 PM
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Totally agree...you simply cannot have too much power.
That's ignoring the fact that PSUs quickly lose efficiency when underutilized. Below 25% load, computer PSUs are much less efficient and provide absolutely no advantage. The best way to size a PSU is so that the idle load power falls in the over 25% rated power range and full load power fall between the 25% and 75% rated power range. Using too big a PSU wastes power and is an unnecessary expense.

Quote:
this is the information super highway. I just gotta have the power!
PSU power has absolutely nothing to do with a PC's information speed or capacity.

Quote:
I have had basic power supplies in the past and never understood why it would sometime crash for no reason. A friend of mine highly involved in electronics asked me about how big my PS was. When I told him, under his advice, I changed it to a bigger model and suddenly, the computer behaved like a brand new one.
That's more likely due to the quality of the PSU than the rated power capacity. Low quality PSUs often provide poorly regulated power or less than the rated power. One that is failing or even slightly overloaded will often provide low voltages or have intermittent voltage dropouts and spikes that cause crashes. If I find a case I like that has a low quality PSU, the first thing I do is toss the PSU. It's not worth the hassle or the risk to other components. A good quality PSU will provide more stable operation, operate longer before failing, fail without damaging other components and easily handle peaks that exceed its rated power. A poorly designed PSU will fail sooner, possibly damaging other components.
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