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The rechargeable lithium battery market was approximately $9.4 billion in 2015 and is projected to grow to more than $11.9 billion by 2020. Portable device batteries remain the backbone for lithium rechargables but the future of lithium batteries is likely the plug-in electric vehicle. Regardless, it’s clear that Li-ion rechargeables are the entrenched energy technology for laptops, smart phones, and all sorts of portable devices. Still they have technical hurdles to address. One weak point for these batteries is their potential to overcharge and fail. This concern is heightened when multiple batteries are charged from a common source in a series configuration. In such a scenario, one battery in the series may become fully charged before others which subjects this battery to an overcharge condition. Series charging is more efficient and will likely be the method for charging electric vehicles.
The above issue has previously been addressed by the use of shunt-style charging circuits to clamp the charging voltage of each series-connected battery to a precise voltage setting. Shunt regulators are inexpensive but they are also highly inefficient due to the amount of energy they dissipate during the shunting action. This dissipation of energy also shortens the lifetime of associated circuitry. Navy researchers have addressed the inefficiency issue with a novel multiple-battery charging device, utilizing a common source, and capable of handling different battery sizes. The system incorporates a power controller with a programmable algorithm which controls the power reduction and battery charging process. Each shunt charging circuit has its own internal voltage comparator in connection with current sensors with precision resistances. Sensors monitor the batteries and feed that information back to a power controller which modulates the charging current.
- Increase in efficiency, a reduction in the likelihood of overcharging conditions, and a reduction in the generation of heat
- Elimination of the need for supplemental cooling, which provides an additional advantage of lower manufacturing costs
- Does not depend on a timed charging cycle
- US patent 7,573,235 available for license