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How do I read a power supply?

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March 25, 2010 7:32:40 PM

I've been hearing that it isn't about how many watts I have, but what I have on the 12 rails. I don't know what that means.

I have a thermal take 600watt purepower.
It says I have


+5v 28a max load
+3.3v 30a max load
+12v 1 18a max load
+12v 2 18a max load
-12v .8a max load
+5 VSB 3a max load



Does the 1 and 2 next to the 12v mean the rails? What's a real anyways?

More about : read power supply

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a b ) Power supply
March 25, 2010 7:42:17 PM

A rail is just a term that we use for the different voltages that come out of the power supply each voltage is considered on its own rail. Your power supply has 2 12v rails pushing 18 amps a peice so a combined total of 36 amps for a 600watt power supply that is a little on the weak side for the 12 volt rail. However depending on your system the Average single Graphics card system that is more then enough to power your system.
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a c 144 ) Power supply
March 25, 2010 7:45:16 PM

The 12 volts specs on the label will tell you the maximum load of each rail. There should be a line under that telling you what the total maximum power is.

Yours doesn't tell you what the max power is:
http://www.newegg.com/Product/ImageGallery.aspx?CurImag...

If your maximum current available is 36 amps, that's average performance. A good 550 watt PSU should be able to produce better than 40 amps.

The 700 watt TT does tell you:
http://www.newegg.com/Product/ImageGallery.aspx?CurImag...

See where it says maximum 12 volt power is 648 watts (54 amps)?
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a c 165 ) Power supply
March 25, 2010 7:49:20 PM

:heink: 
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a c 165 ) Power supply
March 25, 2010 7:50:38 PM

jsc said:


See where it says maximum 12 volt power is 648 watts (54 amps)?


someone paid attention in math class ;) 
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a b ) Power supply
March 25, 2010 8:03:55 PM

Something not mentioned is why the +12V rails are important. These rails provide power for your CPU and the expansion slots (including a graphics card). These components draw the most power. I believe the ram runs on the +5V and I'm not sure about the others. Someone correct me if I am wrong.
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March 25, 2010 10:45:26 PM

Hey thanks guys. I sort of understand now. I just need to pay attention to the 12v. I did get my thermaltake on discount. It was only like $60.00 or so.

I'm concerned about my popwersupply when I upgrade though. I currently have a

E5200 2.5gig dual core with 4 gigs ddr2 ram, a dvd drive, GTX 260 graphics card and 2 hard drives.

I'm upgrading to maybe an AMD AM3 motherboard with a Phenom or Athlon x4 chip. Will my current 600watt 36amp power supply need to be replaced?
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a b ) Power supply
March 25, 2010 10:49:53 PM

Yes it should be fine powering that system. You will only really need to upgrade if you go for a more powerful video card but you will be fine with your current setup and the future AM3 setup.

Good Luck
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a c 92 ) Power supply
March 26, 2010 3:18:57 AM

Quote:
Your power supply has 2 12v rails pushing 18 amps a peice so a combined total of 36 amps


Again, it doesn't work that way. It can work that way, but thats not how you determine the COMBINED 12V amperage. You need to find the statement like JSC did and then do the math. My delta sourced EA500W is my favorite example. Each rail is rated at 22A, but I don't have 44A of power on the 12V rail. I only have 34.
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a c 165 ) Power supply
March 26, 2010 3:24:17 AM

4745454b said:
Quote:
Your power supply has 2 12v rails pushing 18 amps a peice so a combined total of 36 amps


Again, it doesn't work that way. It can work that way, but thats not how you determine the COMBINED 12V amperage. You need to find the statement like JSC did and then do the math. My delta sourced EA500W is my favorite example. Each rail is rated at 22A, but I don't have 44A of power on the 12V rail. I only have 34.



V * A = W

:sol: 
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a b ) Power supply
March 26, 2010 4:18:38 AM

ct1615 said:
V * A = W

:sol: 

P=VI
Don't confuse units with the symbol.

264W on each rail (I=22A and V= 12V) does not mean it will allow a total draw of 528W
Here's a chart from OCZ:
http://www.ocztechnology.com/images/awards/mxsp_wattage...
Note that their 700W PSU has the same number of rails and the same amps per rail as their 600W, yet provides more power across both rails.
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a c 165 ) Power supply
March 26, 2010 4:40:31 AM

enzo matrix said:
P=VI
Don't confuse units with the symbol.

264W on each rail (I=22A and V= 12V) does not mean it will allow a total draw of 528W
Here's a chart from OCZ:
http://www.ocztechnology.com/images/awards/mxsp_wattage...
Note that their 700W PSU has the same number of rails and the same amps per rail as their 600W, yet provides more power across both rails.



not using symbols, simply didn't feel like spelling out amps, volts, watts

glad you can paste and copy a wiki article *golf clap*

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a c 92 ) Power supply
March 26, 2010 4:50:03 AM

Your missing the point. 18A on 12v1 + 18A on 12v2 != 36A. It might in some cases, but that's not the way you figure out how many amps the PSU can provide. You don't have to spell out the words, you can use the correct abbreviations.
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a c 165 ) Power supply
March 26, 2010 4:58:04 AM

4745454b said:
Your missing the point. 18A on 12v1 + 18A on 12v2 != 36A. It might in some cases, but that's not the way you figure out how many amps the PSU can provide. You don't have to spell out the words, you can use the correct abbreviations.


who are you talking to?
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a c 92 ) Power supply
March 26, 2010 5:32:22 AM

Saaiello mostly. First reply.
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a b ) Power supply
March 26, 2010 12:30:38 PM

ct1615 said:
not using symbols, simply didn't feel like spelling out amps, volts, watts

glad you can paste and copy a wiki article *golf clap*

Excuse me? I did not visit wikipedia at all. This comes from my experience in computer engineering.
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March 26, 2010 1:46:20 PM

So how exactly do yu determine the total power on the 12v rail?
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a b ) Power supply
March 26, 2010 9:03:56 PM

Starges said:
So how exactly do yu determine the total power on the 12v rail?

I've been trying to figure that out since I found out that it's not VI+VI. So far, all I can figure out is that you have to check with the manufacturer. If you look at the link I posted, both the 600W and 700W versions have the same amps on the +12V rails and the same number of rails but one supports 500W and the other 550W.
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a c 92 ) Power supply
March 27, 2010 3:36:59 AM

The only way to know before you buy is to look at the label. The manufacturer has to list total power available on the 12V rail(s) combined. Usually written as "12v1 and 12v2 not to exceed 408W" or some other total output number. Do the math, you'll get your amperage. If they don't list it, you can perhaps find a review where they test it. Other then that, you really have no idea.
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a c 144 ) Power supply
March 27, 2010 1:22:05 PM

enzo matrix said:
I believe the ram runs on the +5V and I'm not sure about the others. Someone correct me if I am wrong.

OK. :)  RAM runs of the 3.3 volt rail. It uses a simplified version of the programmable power regulator that the CPU does. Measurements on my first Core2 system indicated that 2 GB of DDR2 RAM running at 2.1 volts pulled 6 amps or 20 watts of power.

Starges said:
So how exactly do yu determine the total power on the 12v rail?

I buy single rail Corsairs now. :D 

But you could read the PSU label (see my two links above) and if the label doesn't tell you the total (like the first), don't buy the PSU.

I also have an Antec 650 watt TP3. It has 3 rails (allegedly), each max rated at 19 amps. The label also says that max 12 volt output is 624 watts (52 amps).
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March 30, 2010 9:39:01 AM

Why is it that some PSUs have lots of amperage (up to 30A) in the +3.3v rail and very little the +12v rail? Apart from RAM, what else does this rail (the +3.3v rail) provide power to? [:fixitbil:1]
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a c 144 ) Power supply
March 30, 2010 9:54:31 AM

Starges said:
Why is it that some PSUs have lots of amperage (up to 30A) in the +3.3v rail and very little the +12v rail?

Obsolete design , dressed up with modern cables.

Apart from RAM, what else does this rail (the +3.3v rail) provide power to? said:
Apart from RAM, what else does this rail (the +3.3v rail) provide power to?

SATA drives. 3.3 volts comes off the orange wires.
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a b ) Power supply
March 30, 2010 12:11:08 PM

Starges said:
Why is it that some PSUs have lots of amperage (up to 30A) in the +3.3v rail and very little the +12v rail? Apart from RAM, what else does this rail (the +3.3v rail) provide power to? [:fixitbil:1]

So they can say it's a 600W power supply when the +12V rails can only provide as much as a modern 300W.
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March 30, 2010 1:55:51 PM

you can find 12V ratings for many units here:

http://forums.guru3d.com/showthread.php?s=80ed7896f1bd1...

The OP's model 12V rating is listed in the specs at Thermaltake as 38A...the label is wrong and missing the third 12V/16A rail this design has. It's a 550W unit btw...TT overrates this one 50W...but it's a good CWT-PSH design.
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March 30, 2010 4:31:18 PM

Best answer selected by tuesday0180.
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