battery power suplpy for power amplifiers possible?

My first successful amp was the 20W Class A amp designed by Douglas Self and published in Electronics World Magazine. As an experiement, I brought 4 cheap 2nd hand car batteries of medium size, and hooked them up to produce the +/-24v (nominal) that the amp needed.

The Amp drew 1.6A quiescent per channel for a total of 3.2A The batteries lasted approx 4 hours before quitting One battery had considerable less capacity than the others, and always went first, I think because it was old. It was nice to have complete absence of hum and noise. The experiement didn't last more than a fortnight, Even I grew weary of 4 car batteries in my room.

I think if you were going to go this route, do it properly and buy some serious batteries, perhaps truck batteries, that would not be anywhere near discharged after a few hours listening, as automotive batteries are not designed to undergo periodic deep discharge and then charging. (They are designed to provide a huge hit of power to start a car, and then provide no power as the alternator powers everything when the engine is running).

Also, you'll still need a power supply to charge the batteries, and you have to decide if it will simply charge the batteries with the amplifier off, or if it will be able to power the amp and charge the batteries at the same time. Note that batteries do not act like capacitors, and provide no smoothing of power supply noise. Charging four large batteries in a reasonible time takes a fair amount of power.

Cheers, Adrian
Hope this gives you something to think about.