# How to figure out battery life of audio amplifier?

I have a design of an audio amplifier. It has some special features but basically it takes in an audio signal does some filtering, and amplifies it through a class D amplifier chip. The chip says it has a 1.7A max current draw, sound played will be music or some signals. I want to power it with 4 AA batteries.

My question is, what current do I use in a mAH/current equation to figure out how long my battery might last. It's not a constant 1.7A since the music played will determine output current.

Also, are there other special considerations for battery life of an audio amplifier?

• There are so many unknowns that the only way to find out is by putting in a set of batteries and see how long they last. You could look at this, it may help candlepowerforums.com/vb/… Commented Sep 12, 2014 at 22:29
• Posting a schematic or at least mentioning what amplifier IC you are using would be helpful. Commented Sep 12, 2014 at 22:30
• You may need D cells - I don't think AA cells will be happy delivering (or trying to deliver) 1.7 amps. Commented Sep 12, 2014 at 23:30
• I'm looking at the TPA2013D from TI. Commented Sep 12, 2014 at 23:32

Taking a standard capacity number for AA (Alkaline, good brand) of 2500mAh, and a conservative average draw of 1 Amp for the amplifier (which is a fairly large draw on AA batteries). Since the Chip has a max VIn of 5.5V, you will be powering with 2 AA in Series, In Parallel, giving 3V and 5000mAh.

It drives up to 2.7 W (10% THD+N) into a 4 Ω speaker. With 85% typical efficiency, the TPA2013D1 helps extend battery life when playing audio.

So given a 4Ω speaker at max, you get 87% efficiency, so the capacity is more like 4350mAh. With a lower operating voltage, that's more like 83 to 80% based on the graphs.

A off the cuff napkin calculation of 4300mAh / 1000mA = 4.3 Hours. Round down for voltage drop and loud songs, I figured on 4 hours max, with GOOD batteries, not cheapo ones.

Of course, max volume, speaker's resistance value, temperature, etc can affect that, but that is your top end without empirical testing, or going with beefier batteries (C, D, etc)

Also, its the "TPA2013D1", not "TPA2013D".

• I guess I was looking for something that included the fact that music would be playing. If I put a sine wave into it, it wouldn't be outputing the full 1A for 4 hours. Commented Sep 13, 2014 at 14:56
• @confused the 1 Amp input is averaged out, at full amplification, with music varying between low and peak volumes. As mentioned, these are napkin calculations for example purposes, and serve as a guesstimate baseline. Commented Sep 13, 2014 at 17:04