Audio Amplifier Battery Life

Thread Starter

Alicec63

Joined Jun 20, 2013
12
Hi,

Say I have an audio amp(MAX9701) connected to a set of 8 ohm speakers - rated at 1W - powered via 2x AAA Batterys...

Assuming the batteries had a rating of 1000mAh. How long would the battery last under constant operation i.e. playing music through an ipod?

The only other thing in the circuit is a boost convertor (MAX856) which keeps the supply voltage at 5V and obiovusly the amps input is connected to a music 'source' i.e. ipod.

I'm sure this is pretty simple, but I think I am probably complicating things in my head... Friday afternoon!

Any help would be much appreciated.

Thanks
 

MrChips

Joined Oct 2, 2009
30,714
Use the formula for power P = I^2 x R
I^2 = 1W/8Ω
I = 0.35A

1000mAh/350mA = 3h

You will be lucky to get 2 hours from two AAA batteries.
 

Thread Starter

Alicec63

Joined Jun 20, 2013
12
Thanks.

Is it really that simple. That will give me the output power. Does it not take into consideration the input voltage i.e. 3V from 2 x AAA batteries? Or the efficiency of the boost convertor and the amplifier?
 

#12

Joined Nov 30, 2010
18,224
MrChips ignored the efficiency of the converter because they are about 90% efficient and the uncertainty factor of the batteries and how high the loudness will be turned up are a lot more than 10%. It's an estimate. It's close enough.
 

MrChips

Joined Oct 2, 2009
30,714
Think conservation of energy.
.3A @ 3V is coming from the battery.
The energy has to go somewhere, either as acoustical energy or as heat loss.
 

bountyhunter

Joined Sep 7, 2009
2,512
1W average power would blow your eardums out if listening through ear phones. I suspect the average power would be less than 0.1W. The easy way to determine the battery life is measure the current when the volume is at the typical level.
 

GopherT

Joined Nov 23, 2012
8,009
0.1 watt is the normal max for headphone listening (per ear) for most commercial devices.

Most headphones are 16 ohm each side. Your milage may vary. I think the OP is trying to connect 8ohm loudspeakers though, not headphones.
 
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