Li-Ion series charger.

[PeterG]

I have a project that runs off a pair of 18650 Li-Ion cells. I would like to build a charge system into the project.

How safe is it to charge these cells in series to 8.4v?
Is there an off the shelf module out there for this sort of thing?

Regards

[Psi]

The risk with charging them in series is if they ever get out of sync, or one deteriorates quicker, you end up overcharging one while undercharging another. Not a good thing with lithium.

Proper series chargers have extra feeds linking to between the cells to monitor their individual voltages.
The cheap chargers don't bother with that and just rely on a thermal switch to cut off the battery connection if any cell starts to get hot (overcharged).

[gregariz]

If you need a 2 cell lithium and can put up with the size the 9v Lithium rechargables could be worth a look

http://www.ebay.com/itm/1pc-9V-600mA-Lithium-Rechargable-Battery-6F22-/260853220484?pt=AU_Electronics_Batteries_Chargers&hash=item3cbc104484

[PeterG]

I looked at the 9v. Howver i need more current, so  am using 18650 cells. I am looking at building a betery charge system into the project so i dont need to remove them for charging.

Regards

[gregariz]

The only higher C 2 cells I know off hand are the sparkfun ones

http://www.sparkfun.com/products/10471

[gregariz]

Just as I replied... I made it to the end of this months circuit cellar...... on the back page is this...
http://www.parallax.com/Store/Robots/AllRobots/tabid/755/txtSearch/charger/List/0/SortField/4/ProductID/758/Default.aspx
but no schematic from what I can see

[PeterG]

Gregariz, that board is ideal. I will wait for stock. Maybe someone in Aus will stock them soon.....

Thanks.

Regards