[goodsound]

Didn't stir much interest over at the amp forum so I thought I'd post it here to see if anyone has any additional comments -

http://www4.head-fi.org/forums/showthread.php?t=164477

 

[JohnFerrier]

If I were to redo my design, I’d go with sealed lead acid. Currently, I parallel alkalines. Though expensive, lithium batteries, I think, have slightly lower internal resistance, than NiMH. Parallel capacitors reduces AC resistance.

 

[mono]

Battery for what, exactly?

There is no magic "just choose this battery type" for a better result, but the battery must be capable of a little more than the continuous power needs of the amp. Beyond that - capacitors. No battery change comes close to simply having enough capacitance, and if there is a worthwhile change from changing the battery, odds are high the capacitance is really what needed changed.

 

[goodsound]

did you read the opening and also the last sentence in my first post in the linked thread ? Batteries for what other than portable players and amps would I post about here ?

Actually current/power capacity of the battery is exactly what I am NOT talking about. Its already ample. Adding too much capacitance has its own problems also.

This is about ac impedance of the battery. It is analogous to power supply impedance.

And it is about the current spike delivering capability of the battery(internal resistance). Music could have as much as +12db spikes, the amp and the power supply(battery in this case) should be capable of meeting that current demand - without any drop in voltage. Dont mistake this for "capacity" (like mah) of the battery. Chances are a 1000mah battery might be able to provide better current spike than a 2800mah battery.

Btw, power supply ac impedance is the same issue that you would run into if you used too much psu filter capacitance (>2200uf typically). So adding capacitance also works only upto a certain point.

 

[mono]

Quote:

Originally Posted by goodsound did you read the opening and also the last sentence in my first post in the linked thread ? Batteries for what other than portable players and amps would I post about here ? Actually current/power capacity of the battery is exactly what I am NOT talking about. Its already ample. Adding too much capacitance has its own problems also. This is about ac impedance of the battery. It is analogous to power supply impedance. And it is about the current spike delivering capability of the battery(internal resistance). Music could have as much as +12db spikes, the amp and the power supply(battery in this case) should be capable of meeting that current demand - without any drop in voltage. Dont mistake this for "capacity" (like mah) of the battery. Chances are a 1000mah battery might be able to provide better current spike than a 2800mah battery. Btw, power supply ac impedance is the same issue that you would run into if you used too much psu filter capacitance (>2200uf typically). So adding capacitance also works only upto a certain point.

You seem desperate to assume something not in evidence.

No, it is not the problem you suggest and capacitors are exactly what is called for. Did I write "just make one cap a larger value"? No. Optimal cap values are used. That doesn't mean one can choose an insufficient supply, you write of peaks as though I might've meant a supply can be chosen that is incapable of near the peak demand which is of course not good.

When you strive for this idealistic battery, all you're doing is trying to replicate a really poor capacitor. A battery has similar behavior as one in that even with low impedance cells, they do in fact drop voltage (even if only to a lower degree) with higher current delivery. It is the same action as capacitors except far inferior to capacitors... optimal capacitors, not just choosing one giant cap.