80 amp PSU?

[Xenozx]

OK, this is just a question Ive had in the back of my head for a while and am currious to see the answer.

How can there be an 80 amp PSU when the plug it is pluged into is a 25 amp 115v source? I believe PSU's are not very efficient and lose about 20-30% of their power so to me even teh 25 amps would be impossible without blowing a fuse, it would be more like 20 max.

Can someone explain this too me?

 

[Oklahoma Wolf]

Because that 80A is at 12v or less. Using the formula P=VI, that works out to 960 watts, which is well under the power able to be provided by that 125v 25A source (that's 3125 watts going by the formula btw).

 

[Xenozx]

Ah I C, thank you....

So a 9 amp floor cleaner is 9 amps at 115 volts, where a PC power supply on a 12v rail is 80 amps at 12v.

so 12v x 9 = 108v

80 / 9 = 9 amps

so maxing out 80 amps at 12 volts would = in theory a 9 amp vaccum cleaner?

makes sense to me atleast.

thanks for the info.

 

[flint338]

Ah I C, thank you....

So a 9 amp floor cleaner is 9 amps at 115 volts, where a PC power supply on a 12v rail is 80 amps at 12v.

so 12v x 9 = 108v

80 / 9 = 9 amps

so maxing out 80 amps at 12 volts would = in theory a 9 amp vaccum cleaner?

makes sense to me atleast.

thanks for the info.

ehhhh...... your math is whacked.

9 * 110 = 990 watts

80 * 12 = 960 watts

basically the same power draw, but remember watts is volts * amps. No idea where you got your numbers..

that being said, any device that can run natively at 110v [without transformers] is going to be a more efficient, that 80 amp PSU is probably going to draw more than 960 watts under load.

also, remember than your amps on your breaker tend to be a lot less than the maximum rated, especially with age. Don't go running a 20 amp (at 110v) device on a 15 amp breaker, like a compressor or a table saw -- you'll trip the breaker every time. But your 80 amp (at 110v) device will be just fine. There's not enough current * voltage [pressure] to trip the breaker, even if it's underrated.

 

[[Spectre]]

Ah I C, thank you....

So a 9 amp floor cleaner is 9 amps at 115 volts, where a PC power supply on a 12v rail is 80 amps at 12v.

so 12v x 9 = 108v

80 / 9 = 9 amps

so maxing out 80 amps at 12 volts would = in theory a 9 amp vaccum cleaner?

makes sense to me atleast.

thanks for the info.

If you have a PC with a 80A 12v rail it most likely is a 1000w total power PSU. That means at the wall it may draw around 1200w at 1000w DC. 1200w/120v=10A

PSU's only output as much power as is neeeded at any given time so the total draw will vary.

 

[Xenozx]

yea, I bought a 700w toughpower, and it says it has 4 rails w/ 20 amps each. I know that it probably isnt really 80a all at one time, but I was just always currious how it got those #'s due to it being plugged into a 15 or 25 amp outlet. IM not above average when it comes to current and voltage and such, so I didnt know nore think about the principles of voltage and watts and such.

my math was as follows and may be completely wrong.

125v = 25 amps

so 12v x 11 = 126v

80amps / 11 = 7ish amps being pulled from the 25 amp source. my original math was taking into consideration it was a 115v source.

so by my calculations, which are most likely completely wrong, that 700 watt PSU, when being maxed out @ the 80 amp pull @ 12v is taking up 7 amps at the 125v outlet, shich is only half of a 15 amp circut, or 7 of 25 from a 25 amp circuit.

thanks again tho

 

[masteraleph]

yea, I bought a 700w toughpower, and it says it has 4 rails w/ 20 amps each. I know that it probably isnt really 80a all at one time, but I was just always currious how it got those #'s due to it being plugged into a 15 or 25 amp outlet. IM not above average when it comes to current and voltage and such, so I didnt know nore think about the principles of voltage and watts and such.

my math was as follows and may be completely wrong.

125v = 25 amps

No. First of all, assume 115v as a standard for AC 110-120v outlets.

So, a hypothetical 25 amp circuit will result in:

115V*25A= 2875W.

Wattage is your power measurement, derived from P(Watts)=I(current in Amps)*V(voltage)

so 12v x 11 = 126v

You are, I think, equating voltage and wattage here. Don't do so. If you really wish to do so, roughly equate a device using 1 Amp from a 115V wall socket as pulling 115 watts and a device using 10 Amps from a 12 volt rail at 120 watts.

80amps / 11 = 7ish amps being pulled from the 25 amp source. my original math was taking into consideration it was a 115v source.

so by my calculations, which are most likely completely wrong, that 700 watt PSU, when being maxed out @ the 80 amp pull @ 12v is taking up 7 amps at the 125v outlet, shich is only half of a 15 amp circut, or 7 of 25 from a 25 amp circuit.

thanks again tho

Again, take this simpy. The maximum output for a PSU putting out 80 amps on a 12 volt line is 960 watts. Clearly that isn't the case here. To be safe then, let's assume that the 700 watt PSU is capable of actually putting out a total of 650 watts over the 12v rail(s). Therefore, 650w/12v= 54 amps, not 80. Note that most modern PSUs are actually single rail devices and a figure of 54 amps is roughly in line with what should be expected from a 700 watt PSU.

Of course, PSUs are not 100% efficient. Let's presume an 80% efficiency on this one. Therefore 700watts/.8= 875 watts from the wall.

That gives us a rough figure of 7.6amps being drawn from the wall at maximum draw.