As with NiCd or NiMH cells, Lithium batteries can be wired in series to increase voltage. Unlike NiCd or NiMH cells, the Lithium cells can also be wired in parallel to increase capacity and current delivery.
A combination of series and parallel Lithium cells can be used to create a more capable flight pack for powering larger motors or increasing flight duration. A common designation seen to describe the configuration of multiple cell Lithium packs is the XsYp label where X is the number of cells in (s)eries and Y is the number of cells in (p)arallel.
The series/parallel diagram below shows one pack of four Lithium cells in series and one pack of four Lithium cells in parallel. When the cells are placed in series, the voltage per cell is simply added. The four cell Lithium pack would measure 4*4.2v or 16.8 volts unloaded. Its pack designation would be 4s1p or simply 4s. When the cells are placed in parallel, the voltage remains the same but the capacity and current delivery are added. If the four cells are the Kokam 145mAh Lithium cells then the resulting pack would measure 4.2v unloaded and have a capacity of 145*4 = 580mAh (or 4C). The current delivery capability would also jump from about 700mA continuous current per cell to about 2800mA continuous current for the 4-cell combination. The short term peak current delivery for this particular cell is about double that so our 4-cell combination would deliver about 5600mA for 10-20 second bursts. Its pack designation would be 1s4p or just 4p.
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