voltage monitor

[GioppY]

Any suggestion where to start ?

Perhaps you can start from here:
It is for car battery; but you can adjust for any voltage
http://www.pctuner.net/articoli/Pic/..._-_Datalogger/

Regards
Gianni

[BrianT]

Li Ion cells are easily damaged if they drop below 3 volts. Run them flat and they lose most of their capacity and instead of being a 1500 mAH capacity, they drop to maybe 1/4 of that capacity. In a series string of 4 cells I suggest you need 4 analog channels on your PIC, say a PIC16F88. You can measure the first cell directly but you need voltage dividers off cells 2, 3 and 4 to ground so you can measure V1, V2, V3 and V4.

V1 is the first LiIon cell and must not be allowed to fall below 3 V. V2-V1 gives you the voltage of the second cell. V3-V2 gives you the voltage for the third cell, etc.

The PIC16F88 needs no crystal and would be a very cheap solution for up to 7 series cells.

HTH
Brian

[aftab]

Hello,

Thanks everyone for the tips and links. I am getting the parts now from e-bay.
Rentron is always my favourite site for tutorials for amateur like me(thanks mkit)

On way is 12c672. And trying to get 16f877 - seems a bit more expensive.

From Wikipedia got valuable info on li-ion cells(thanks briant).

Got $1.59/each (X 8pc) charging circuit from batteryspace.com. The charger works fine but charging is stopped once the voltage reaches 4.2v and stops discharging when <3.0v. It is not current limited and the batteries do not get warm in the process of charging. So, I guess it does not charge the batteries to their full capacity. Interested people might find it useful for ready-made low cost chargers.

This micro controller world is really fascinating.

thanks
Aftab.