Electronic – Amplifier power draw


I'm working on a project where I'm going to drive 2 x 8-ohm loudspeakers using 1 (or more) car batteries and a Class-D amplifier. The setup is going to be used at a festival, so I need maximum efficiency from my system.

My question is, how does the amplifier draw power? Does it keep a constant load on the battery or does it vary according to the power needed from the loudspeakers? If I simply hook the amplifier up and simply vary the amplitude of the audio-signal, will it use power accordingly, or?

I'm considering this amplifier at the moment:
http://classdaudio.com/products/600w-class-d-power-amplifier.html since I should be able to drive it with 2-batteries in serial. Anything I should notice?

Best Answer

At 100% efficiency, the power drawn from the battery will be exactly the same as the power output to the speaker.

Real amplifiers are never 100% efficient, but a class D amplifier can be pretty efficient. TI claims > 88% for the chip used in the amplifier you are looking at.

You should really look at the tas5630 datasheet.

Here is power wasted vs. power output. It is nearly a straight line. Notice a few watts are drawn all the time, even with zero output:

enter image description here

Another graph to study carefully is this one. Maybe two car batteries in series (for 24V) is not enough voltage to get your desired power output:

enter image description here