Your charger, as I can visualise it, should consist of three major blocks:
- 2-2.2A current source (fast charging, 1C current for 2200mAh battery)
- (as many channels as you need) 3-cell battery charger with ON/OFF function
- microcontroller to supervise the whole circuit
First, look at the Li-Ion battery charging characteristics ..
From the attached picture you can see that the charger should start charging battery using current-limited constamt voltage source ..
A constant voltage charger sources current into the battery in an attempt to force
the battery voltage up to a pre-set value (usually referred to as the set-point voltage or set voltage) ..
Once this voltage is reached, the charger will source only enough current to hold the voltage of the battery at this constant voltage (hence, the reason it is called constant voltage charging) ..
To build a 2A current source I suggest that you use the LM2576 .. se example below ..
The charger itself can be based on the LM3420-12.6, as the target voltage for a 3-cell Li-Ion battery is 3 x 4.2V = 12.6V ..
And the rest can be build around the PICAXE-18X microcontroller ..
Regards,
IanP