# calculation

#### alyeti

Aug 15, 2010
2
Hi

something that always confuses me,

If an amplifier uses 24v rated at 15Amps and has a power output lets say of 300watts

what would be the current drwan in AC? as in if it also runs at 240v ac same output 300 (speaker output) watts, how do i work out how much current it will draw, for example if it says that it is

rated power consumption is 238w
Ac operation at rated output is 520w

Is current still worked out the same for AC , i am getting old so havent done this in a while LOL

2.2Amps AC???? current = power/240v?

help

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
OK, there's lots of things to consider.

Firstly, if the amplifier is rated at 24V 15A, that's a max input power of 360 Watts. That's a good sign, if it was less than 300W you might begin to worry...

Secondly, the output is 300W -- is that RMS, Peak, or one of the many bullshit measures that seem to allow amplifiers to be rated in kilowatts and still get powered by batteries.

Let's assume that the output is 300W RMS.

You already know that it draws a max of 15A at 24V, which is 360W. If it has a 100% efficient power supply with current drawn evenly (and in phase with) the voltage, then the max current would be 360/240 = 1.5 A

The power supply (if of fairly simple construction) will be far less than 100% efficient, and will also tend to draw current unevenly across the mains cycle (typically only at the peaks of the waveform). In this case the power requirement could be (say) 450W and the max current could easily exceed 5A.

I'm not certain if those examples are actually what it does say, or something you've made up.

#### alyeti

Aug 15, 2010
2
hi the examples are given are actual, so can i assume that i could give myself upto 5Amps and that would cover it? as originally i thought only a couple of amps

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
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