Q-59: I read that you must set your Li-Poly battery charger to the number of cells being charged (although some chargers will do this automatically). The large chargers that I see advertised have a 10-11 cell maximum capacity. How do you charge a 3S4P Li-Poly battery pack that has a total of 12 cells? Do you have to use two chargers or can a 10-11 cell charger handle the extra cell?
A-59: A 3S4P Li-Poly battery pack is three cells in series, then four of those (three-cell sets) are placed in parallel. Now here is the trick and I’ve said it repeatedly—you set the cell count to the number of cells connected in series. So in this case you set the charger (or some chargers will set themselves automatically!) to three cells. The number of cell sets in parallel and the capacity rating of those cells, will tell you how much charge current to set in your charger.
The charge current must always be set manually. Let's say your Li-Poly cells
are rated at 1000 mAh (which is the same as 1.0 amp/hr). You would take 1.0 x 4
(remember 4 sets in parallel!) and set your charger to 4.0 amps charge current.
To summarize, your Li-Poly battery pack, consisting of a total of 12 cells would
be set at three cells and a 4.0 amp charge current. That pack should attain
about 90% of full charge capacity in approximately one hour.
You can easily use a single charger to charge this 3S4P pack. My suggestion
would be to use the Astro Flight Model 109 Lithium charger (green front panel
label). It has the capability of charging from 1-9 Li-Poly cells at currents
continuously selectable from 50 mA up to 8 amps.