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CHARGING DATA

The power supply is based on a pair of two AA NiMH-cell battery packs. These packs provide a nominally fully charged voltage of approximately 2.5 V. In the completely discharged state, the output voltage from the NiMH packs is approximately 1.25 V. The charging time for the batteries in various states of discharge is summarized in Table 1.

The nonlinear charging rate is consistent with the results projected from the datasheets for the batteries used in this supply. The data indicates that fully charging both battery packs overnight (6 h) is certainly feasible. Each pack is rated at 3,200 mAh, so the supply is capable of providing in excess of the required 100 mA of current continuously over a single daytime period. Although we didn’t investigate operation with battery packs other than the NiMH type, the performance of the LTC1325 battery-management IC can be optimized (through both hardware and firmware tuning) for a certain type of battery.