[sdiy] silly question about NIMH batteries

[Richard Wentk]

At 15:26 11/06/2006, Bert Schiettecatte wrote:
>Hi All,
>
>
>I was looking at these AAA NiMH rechargeable batteries that are being sold 
>in stores everywhere and I was wondering if it was possible to get several 
>simultaneous voltages from them without the need for regulators? To 
>clarify what I'm talking about : each battery is 1.2V, so if you put 4 
>batteries in series, that would give you 4.8V. But could it also give you 
>1.2V, 2.4V and 3.6V all at the same time without having to use a regulator 
>for each of these voltages? Would it cause problems if I drew current from 
>each of the cells that is in series with the other ones?

You can't use batteries to provide a stable voltage, because:

1. The chemical process that drives each cell depends on temperature and 
remaining charge.

2. The effective series resistance inside each battery means the voltage 
varies according to current load.

If you pile them up in series, you multiply these effects up the tree for 
each extra battery you add.

Richard