Alex I. Torres wrote:
>
> Hi All!
>
>  I'm working now at one project, using C73, powered
> from Panasonic 3.6V 300mAH NiCd (from cordless phones)
> with MAX631 (3.6->5v convretor).
>  The average current from the battery is 30 mA.
> I have LCD display and one free C73's ADC input, and I
> want to display the "Low Battary" symbols
> in 3 steps : full,middle, low.
>  Now I connected ADC input to battary, and the problem is
> what values a must have as a limit to each step?
You will have to get the manufacturer's discharge curve for
30mA. Measuring the voltage is not a good indicator, however.

>
>  Another problem - this project must be as cheaper as
> possible, so I need very very simple charger. What happens,
> is I use simple AC-powered 12v supply and connect it with
> then battery with (how?)mA current source ?

There is no easy way. The simplest method would be a constant
current source with a voltage setpoint charge stop. Remember,
however, that you need enough current to overcome the reverse
charge when the battery is flat. This current can also be
enough to overcharge the battery, so a fast charge/trickle
charge works best.

You could do it with a transistor, an opamp, a zener, and a few
resistors.

The easiest way to destroy NiCds is to overcharge them.

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za
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