How to recharge Lithium ion batteries via - simple circuit.

as unserstand it you just need a current-limited voltage source.

| | +---[220]--+ | | [R2] [1K] | | ---------------------------+----------+--->

a low value resistor at X slow the charging down as the voltage reaches the set point.

? I'm not sure I understand your diagram, as the formatting was lost.

By coincidence I stumbled on a circuit by Colin Mitchell who also uses LM317 as a trickle charger to charge LI-ion.

He claims :-

"Believe it or not, you can mix any size and type of cell with this circuit as each will become fully charged after a period of 2 days or more, without you having to think about the situation. You can mix any type of cells (NiCad, Li-ION, NiMH) and any size (AA, C or D) and they will gradually charge according their own characteristics and capacity."

See -CIRCUIT NUMBER 3: from

This looks safe, but a lenghty way to recharge.

Yep

Basically correct.

You need to switch your reader to a fixed pitch font.

IMO the voltage regulation in Jasen's circuit is a bit rough.

(shudder!)

It is a trickle charger with a constant current. That is fine for NiXX chemistries where modest over-charging is acceptable and will indeed equalise the state of charge (SOC) of a series string of cells.

Unfortunately, Lithium-based cells require a well-controlled (and current-limited) VOLTAGE SOURCE. That circuit will NOT provide that - trickle charging a Li-Ion/LiPo cell will result in a progressively increasing terminal voltage until something breaks.

In detail, sensible Li-Ion (etc) chargers provide (using as an example the numbers from a commercial charger I designed years ago for cells such as 18650) a 1A current limit and 4.20 volt voltage. On initial connection, charge current is 1A and the terminal voltage rises as the cell charges. When the voltage reaches 4.20, it stops rising and the current progressively tapers off. Usually commercial chargers will stop charging completely when the current has tapered down to 10% of the current limit value, although this is not critical, but the applied voltage NEVER exceeds the target value.

Anyone using a trickle charging arrangement on Li-Ion/LiPo cells is foolhardy.

Fixed font does provide a better view. :)

Thanks

Thanks.

"foolhardy" I can tell you're being polite, unlike some here....