Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1996-11-27
1997-11-25
Wong, Peter S.
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
320 21, 320 15, 320 32, H02J 700
Patent
active
056916230
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates generally to automatically regulated charging systems for a variety of rechargeable batteries and more particularly to a charging system that progressively self-adjusts to the top-of-charge voltage of the battery by interacting with the terminal voltage of the battery, in each one of a series of periodic intervals (steps).
BACKGROUND OF THE INVENTION
In order to charge different types of batteries (nominal voltage, capacity, chemical components), the automatically regulated chargers of prior art, need first to identify each different type so that they can adjust accordingly their operating parameters for each corresponding type. But, since this identification can not be done by such a charger only on the basis of the voltage that the battery is presenting at its terminals, it becomes necessary to externally support these chargers either by equipping them with special battery housings or by placing electrical components on the batteries or eventually by using specially adapted batteries, in a way that all of these could provide to the charger an electrical Signature of each battery type. This certainly limits, physically, the use of these chargers only to those adapted batteries or to those batteries that each charger is designed for.
Therefore, it could be useful for a charger to be able to charge each one of a variety of batteries without needing to identify each different type and therefore without any external support with the consequent limitations.
The use of high charging rates, through the whole charging time, causes wear and tear to the battery. As the battery approaches full charge, its need for energy is decreasing and can not consume all of the charging current and so the rest of it is transformed to heat and gas evolution which causes tear and wear to the plates and separators and water loss to the electrolyte of the battery. This could happen, also, from the beginning of the charging when the battery is in a poor condition (age, discharged for a long time, abnormal sulfatation, etc.).
Also, constant voltage charging, under certain conditions, could cause wear and tear to the battery and sometimes could drive to thermal runaway which to certain sealed batteries (NiCd) results to battery explosion.
Therefore, it could be useful for a charger to charge a battery fast without causing any harm to it, by adjusting its operating parameters according to battery's state, in the beginning and repetitively until the end of the charging process.
Various factors, like the age of the battery, heat and high charging rates contribute to reduce the top-of-charge voltage, and so it becomes impossible to detect a formerly fixed higher value, for those chargers that relay upon the detection of a predetermined value that the terminal voltage of the battery has to reach (representing the top-of-charge state) to terminate the charging.
Such factors, sometimes, could cause short circuits (because of dendritic whiskers) between battery plates, which appear as droppings in the charging voltage and, eventually, could drive to abruptly end the charge, for those chargers that relay upon the detection of a selected slope of the charging voltage, versus time (a NiCd battery charging characteristic), to decide for a top-of-charge state of the battery, to terminate the charging (.DELTA.V charging).
Moreover, since these short circuits increase the flow of the charging current, they could eventually mislead those chargers that relay upon the monitoring for a threshold value of the charging current, to terminate the charging.
But also, the loose character of monitoring with external temperature sensors or thermal switches (affected by ambient temperature) for a threshold value of the battery's temperature, for those chargers that relay upon this value in order to terminate the charging, could cause wear and tear and premature aging of the battery from high heat and gassing, because of the, repetitively, delayed termination of the charging.
Therefore, it could be useful for a charger to
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Shin K.
Wong Peter S.
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