battery driven stuff

[Harry Bissell]

Hi Martin:  inline

Martin Czech wrote:

> >From time to time one needs battery supply, e.g. if you want to play
> your little synth at the beach... (WASP), or if you need a little mic
> preamp for outdoor recording etc..  Usually severall NiCd or other
> elements are cascaded to get a reasonable voltage.
>
> The problem is that if one element is weaker then the others the voltage
> will collapse, in the beginning everything looks ok, but after a few
> minutes it's over even if there is enough charge in the other elements.
>
> Another thing is voltage regulation, I have no problems to waste several
> W for a linear (and thus quiet) regulator, but for battery stuff power
> consumption is an issue.
>
> Therefore I'd suggest the following:
>
> Instead of serial cascade, just use the elements in a parallel way.
> The output voltage of NiCd is stable over discharge, so I hope there
> will be no large currents as the elemets will fight against each other.
>
> I don't know much about batteries and such, but I'm getting better. Could this
> parallelism be a problem for element lifetime or performance?
>
> If an element gets weak in serial connection, there will be also
> currents through the element chain (if the circuit still works).
> This will also stress the weak element further.
>
> Ok, if this works we have a rather stable 1.2V supply that should work
> until the last element has lost it's charge. In order to get to some usefull
> voltage I would suggest a step-up switcher. Yes I know, noise and problems.
>
> Do you think that a 1.2V to 5V or even 1.2V to 20V ratio is possible
> with good performance?

Performance is related to the efficiency of the switcher, and power in = power
out.

so 1 volt at 20 amps = 20 volts at 1 amp * the efficiency loss

can be done. lower voltage batteries often have large currents.

Don't overlook sealed lead acid cells (used in alarm systems etc) they have
good recharge characteristics, they are just er.... heavy as lead !!! Also they
are usually
12VDC, so a simple inverter is possible.

Maxim makes a LOT of battery conversion IC's including those for 1.2VDC

>
>
> I guess the usuall switcher ICs won't work with such a low voltage (1.2V),
> so at least the oscillator must be homebrew, the regulator can then live
> from the higher output voltage.
>
> Any battery gurus out there?
> What's the proper name for rechargeable (NiCd) elements and

around here Rechargeable

>
> how do you call non rechargeable elements (MgZn and the like)?

Primary Battery

this helps ??? H^) harry

>
>
> m.c.