Hi guys,
Last couple of 10days I have been scrouging forums looking to demystify and throw some light upon the power ratings written at the back of the PSU. I know, nothing beats actually getting the PSU and testing it out, but it does save a lot of time when you are able to make intelligent choices without having to "mis"invest in poor/midiocre hardware.
So here goes:
Usually power supplies are rated separately for their different rails. The usual rails one finds on current PSUs are +5, +3.3, +12V1, +12V2, +5Vsb, -12V. -5V, +12Vsb are unusual and not a requirement, but are sometimes put in by PSU manufactures as speciality. Also in case of single rail PSUs, +12V2 is absent and only a single +12V rail is present. Now to the crux of the matter, the rail ratings:
I will approach this with a example:
The above is the exact power ratings of a ANTEC TRUEPOWER II 550W EPS12V PSU.
The most important line in the above table is the last line,
The PSU is rated for 550W, and the 4 rails (+5, +3.3, +12V1, +12V2) are rated together at a max of 530W. So that leaves 20W for the the 2 other rails (+5Vsb and -12V) and we see that calculating the wattage of the +5Vsb and the -12V rails, we get approx 22W (5V x 2A = 10W + 12 (not -12) x 1A = 12W = 22W) Its not a mathematical calculation error by the part of Antec, its a very valid specification table (more on that later.)
Now, coming to the main 4 rails, we see that my calculating the wattage by multiplying the rails and their amperage we get:
5V x 40A + 3.3V x 32A + 12V x 19A + 12V x 19A = 200W + 105.6W + 228W x 2 = 761.6W
Now, either some people are very weak in their maths over at Antec or something weird is going on. Surely they mention that max power draw on the 4 rails is 530W and the calculated value comes up to 761.6W? Well the truth is a bit complicated, and to really appreciate it we need to look at some numbers:
*assume that the 2 low power rails, +5Vsb and -12V are loaded to max and lets take them out of picture*
The MAX ampere ratings given below the rails are the MAX that can be draw from that particular one at any given time, keeping in mind the fact that other rails will have lesser power available to them.
The above computations should make it preety clear to anyone that the max ampere ratings mean "jack" if they arent backed up by some real estate power (read Watts) from the PSU.
Hope the above has helped some people in understanding the mystery behind the ratings, because it took me a good while to actually get some solid facts rather than just presumptions.
Regards,
Karan
Last couple of 10days I have been scrouging forums looking to demystify and throw some light upon the power ratings written at the back of the PSU. I know, nothing beats actually getting the PSU and testing it out, but it does save a lot of time when you are able to make intelligent choices without having to "mis"invest in poor/midiocre hardware.
So here goes:
Usually power supplies are rated separately for their different rails. The usual rails one finds on current PSUs are +5, +3.3, +12V1, +12V2, +5Vsb, -12V. -5V, +12Vsb are unusual and not a requirement, but are sometimes put in by PSU manufactures as speciality. Also in case of single rail PSUs, +12V2 is absent and only a single +12V rail is present. Now to the crux of the matter, the rail ratings:
I will approach this with a example:
The above is the exact power ratings of a ANTEC TRUEPOWER II 550W EPS12V PSU.
The most important line in the above table is the last line,
Code:
* +5V, +3.3V, +12V1, 12V2 maximum output 530 Watts max.The PSU is rated for 550W, and the 4 rails (+5, +3.3, +12V1, +12V2) are rated together at a max of 530W. So that leaves 20W for the the 2 other rails (+5Vsb and -12V) and we see that calculating the wattage of the +5Vsb and the -12V rails, we get approx 22W (5V x 2A = 10W + 12 (not -12) x 1A = 12W = 22W) Its not a mathematical calculation error by the part of Antec, its a very valid specification table (more on that later.)
Now, coming to the main 4 rails, we see that my calculating the wattage by multiplying the rails and their amperage we get:
5V x 40A + 3.3V x 32A + 12V x 19A + 12V x 19A = 200W + 105.6W + 228W x 2 = 761.6W
Now, either some people are very weak in their maths over at Antec or something weird is going on. Surely they mention that max power draw on the 4 rails is 530W and the calculated value comes up to 761.6W? Well the truth is a bit complicated, and to really appreciate it we need to look at some numbers:
*assume that the 2 low power rails, +5Vsb and -12V are loaded to max and lets take them out of picture*
The MAX ampere ratings given below the rails are the MAX that can be draw from that particular one at any given time, keeping in mind the fact that other rails will have lesser power available to them.
Code:
RATINGS:
[COLOR="Red"]5V: 40A, 3.3V: 32A, 12V1: 19A, 12V2: 19A[/COLOR]
5V: 40A, 3.3V: 32A, 12V1: 19A, 12V2: 19A, [COLOR="Red"]NOT OKAY, LOAD = 761.6W > 530W[/COLOR]
5V: 40A, 3.3V: 32A, 12V1: 10A, 12V2: 10A, [COLOR="Red"]NOT OKAY, LOAD = 545.6 > 530W[/COLOR]
5V: 36.8A, 3.3V: 32A, 12V1: 10A, 12V2: 10A, [COLOR="Green"]OKAY, LOAD = 530W <= 530W[/COLOR]
5V: 40A, 3.3V: 27.2A, 12V1: 10A, 12V2: 10A, [COLOR="Green"]OKAY, LOAD = 530W <= 530W[/COLOR]
5V: 17A, 3.3V: 20A, 12V1: 18A, 12V2: 13A, [COLOR="Green"]OKAY, LOAD = 524W <= 530W[/COLOR]
5V: 20A, 3.3V: 20A, 12V1: 18A, 12V2: 13A, [COLOR=Red]NOT OKAY, LOAD = 539W[/color]
5V: 10A, 3.3V: 13.3A, 12V1: 18A, 12V2: 18A, [COLOR=Green]OKAY, LOAD = 526W <= 530w[/color]The above computations should make it preety clear to anyone that the max ampere ratings mean "jack" if they arent backed up by some real estate power (read Watts) from the PSU.
Hope the above has helped some people in understanding the mystery behind the ratings, because it took me a good while to actually get some solid facts rather than just presumptions.
Regards,
Karan
so will read more into it later.
.
