Power Supply Voltages

[lukesterboy]

Hi i just have a quick question on power supply voltages, it's just out of interest.

 

In the picture i've attached i know the formula is (watts = volts x amps). For the +12V Rail in the picture doing volts x amps gives you the correct number. (+12V rail, 83.3 x 12 = 1000w (ruffly, 999.6w to be precise))

 

But when you get to the 3.3v and 5v rail the wattage is combined. How is this number calculated because doing (3.3 x 25 = 82.5) + (5 x 25 = 125) = 207.5, this can't be correct since it shows 150W. So my question is, how is this number (150W) calculated?

[MorganO]

8 minutes ago, lukesterboy said:

-snip-

does it matter? honestly?

[lukesterboy]

1 minute ago, KOMTechAndGaming said:

does it matter? honestly?

, it does to me.

[MorganO]

1 minute ago, lukesterboy said:

, it does to me.

tried asking corsair directly?

[lukesterboy]

2 minutes ago, KOMTechAndGaming said:

tried asking corsair directly?

Thought i would get a faster reply here. Plus people at corsair our just going to be support agents i highly doubt they know this information.

[Mira Yurizaki]

14 minutes ago, lukesterboy said:

Hi i just have a quick question on power supply voltages, it's just out of interest.

 

In the picture i've attached i know the formula is (watts = volts x amps). For the +12V Rail in the picture doing volts x amps gives you the correct number. (+12V rail, 83.3 x 12 = 1000w (ruffly, 999.6w to be precise))

 

But when you get to the 3.3v and 5v rail the wattage is combined. How is this number calculated because doing (3.3 x 25 = 82.5) + (5 x 25 = 125) = 207.5, this can't be correct since it shows 150W. So my question is, how is this number (150W) calculated?

 

It's the maximum amount on that rail can provide along with the maximum combined on those two rails. So you can have something like 25A@5V for 125W but you only have 25W leftover for the 3.3V rail (so that's like 7-8A). Otherwise if you max out the 3.3V rail, you only have about 50W left for the 5V rail (or 10A).

 

Most power supplies these days only produce 12V power. The 3.3V and 5V rails siphon off that using DC-to-DC converters.

[W-L]

14 minutes ago, lukesterboy said:

Hi i just have a quick question on power supply voltages, it's just out of interest.

 

In the picture i've attached i know the formula is (watts = volts x amps). For the +12V Rail in the picture doing volts x amps gives you the correct number. (+12V rail, 83.3 x 12 = 1000w (ruffly, 999.6w to be precise))

 

But when you get to the 3.3v and 5v rail the wattage is combined. How is this number calculated because doing (3.3 x 25 = 82.5) + (5 x 25 = 125) = 207.5, this can't be correct since it shows 150W. So my question is, how is this number (150W) calculated?

The 5V and 3.3V on the PSU are derived from the 12V rail and stepped down so the 150W is the maximum capacity they can output. 

[lukesterboy]

2 minutes ago, M.Yurizaki said:

It's the maximum amount on that rail along with the maximum combined amount on those two rails. So you can have something like 25A@5V for 125W but you only have 25W leftover for the 3.3V rail (so that's like 7-8A)

 

Most power supplies these days only produce 12V power. The 3.3V and 5V are siphoned off that using DC-to-DC converters.

Ok. I see what you mean.

 

Yeh, i know about the DC to Dc converters. I would have guessed the 12V is probably converted to the correct voltage the cpu wants also? Rather than feeding it a direct 12V.

[Mira Yurizaki]

Just now, lukesterboy said:

Yeh, i know about the DC to Dc converters. I would have guessed the 12V is probably converted to the correct voltage the cpu wants also? Rather than feeding it a direct 12V.

Yes.

[lukesterboy]

2 minutes ago, W-L said:

The 5V and 3.3V on the PSU are derived from the 12V rail and stepped down so the 150W is the maximum capacity they can output. 

Ohh, i see what you are saying. Hence why the maximum watts is 1000 and the 5V and 3.3V watts are taken out of that total. So the 12V is really only working at say 20A when the 5V and 3.3V outputs are working at there full? It decreases the amps on the 12V rail which decreases the watts the 12v rail is outputting leaving more watts that can be used by the 5V and 3.3V outputs? If that makes sense.

 

 

[W-L]

Just now, lukesterboy said:

Ohh, i see what you are saying. Hence why the maximum watts is 1000 and the 5V and 3.3V watts are taken out of that total. So the 12V is really only working at say 20A when the 5V and 3.3V outputs are working at there full? It decreases the amps on the 12V rail which decreases the watts the 12v rail is outputting leaving more watts that can be used by the 5V and 3.3V outputs? If that makes sense.

Yes, if you have something that had a power draw of 150W on the 5V and 3.3V rails it would lessen the total wattage of your 12V rail to 850W as it takes the 12V to be stepped down. 

 

In any modern system this is not much of a worry as not too many devices require a large 5V or 3.3V power. 

[lukesterboy]

7 minutes ago, W-L said:

Yes, if you have something that had a power draw of 150W on the 5V and 3.3V rails it would lessen the total wattage of your 12V rail to 850W as it takes the 12V to be stepped down. 

 

In any modern system this is not much of a worry as not too many devices require a large 5V or 3.3V power. 

Ok. What components do use 5V or 3.3V? I'm guessing CPU and PCI-E devices use the 12V and step it down to the voltage they desire?

[W-L]

Just now, lukesterboy said:

Ok. What components do use 5V or 3.3V? I'm guessing CPU and PCI-E devices use the 12V and step it down to the voltage they desire?

Very few really the motherboard has a couple of 5V and 3.3v inputs, it's older systems that relied heavily on it where most theses days will take a 12V input and on the motherboard itself do the step down and voltage regulation for other components on the board as it's more accurate and precise. 

[lukesterboy]

5 minutes ago, W-L said:

Very few really the motherboard has a couple of 5V and 3.3v inputs, it's older systems that relied heavily on it where most theses days will take a 12V input and on the motherboard itself do the step down and voltage regulation for other components on the board as it's more accurate and precise. 

Interesting. What is the -12V Output for?

[W-L]

Just now, lukesterboy said:

Interesting. What is the -12V Output for?

Basically obsolete at this point and time, older systems required it for the RS serial looking type ports. 

[lukesterboy]

1 minute ago, W-L said:

Basically obsolete at this point and time, older systems required it for the RS serial looking type ports. 

Oh ok.

 

Well thanks for clearing up these bits of information guys.