Electricity: battery or capacitor charging or discharging – Battery or cell charging – With detection of current or voltage differential
Patent
1996-10-23
1998-08-04
Wong, Peter S.
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With detection of current or voltage differential
H12J 704
Patent
active
057899037
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method of, and apparatus for, processing rechargeable batteries. The term "processing" applies to the conditioning of new batteries, the reconditioning of used batteries or new batteries which may have degenerated due to non-use, and also (in its broadest sense) the recharging of batteries while they are being used in a work situation. This process can be done prophylactically.
The batteries which are likely to be most commonly the subject of processing according to the invention are of the sealed nickel cadmium type although the invention may be applied to other batteries in suitable cases. Batteries of the sealed nickel cadmium sort suffer from several defects. The defects are: each other, and for such differences to be amplified by repeated use. active form when the battery is not being used. Also, in the case of batteries that are not used to their fullest capacity, that part of the active material that is left unused may assume the less active form.
The battery defect known as "memory" is sometimes due to either of these defects. gases produced are principally hydrogen and oxygen. The cells have been designed to reuse any oxygen generated but they generally cannot reuse the hydrogen. Since the cells are sealed excessive amounts of hydrogen will cause them to vent and eventually degrade. The generation and expulsion of hydrogen from the cell may constitute an explosion hazard, and also reduce the cell capacity by causing loss of electrolyte.
The problem of uneven charged capacities among the cells of a battery can often be fixed by over-charging the battery. This procedure will be successful when it is only the charged capacity that is uneven among the cells and the intrinsic capacities of the cells are well matched. The procedure of over-charging for this purpose is known as equalisation charging.
The discharge of batteries either as part of battery processing or by use of the batteries in battery operated equipment carries certain risks when the charged capacities of the cells of the battery are not well matched. The main problem occurs when the lowest capacity cell becomes completely exhausted during discharge. If discharge continues beyond this point, the exhausted cell generates hydrogen with its associated problems. The intrinsic capacity of the cell so over-discharged may be further degraded. To reduce the likelihood of over-discharge of cells, equipment which discharges batteries is generally designed to stop discharging when the battery voltage falls to about 1 volt per cell or, for example, to 10 Volts for a 12 Volt, 10 cell battery. This procedure works well for batteries with few cells but is increasingly unreliable as the cell count grows. For batteries with larger cell counts, matching of the intrinsic cell capacities within the battery is considered essential. If the intrinsic cell matching attained during manufacture degrades due to use (or even non-use) or abuse, the battery may rapidly become ineffective or even dangerous.
In FIG. 1 of the accompanying drawings, the discharge voltage vs time of a well matched battery is shown undergoing a steady decrease in graph 1. This can be compared to graph 2 which shows the discharge voltage vs time of a battery in which one cell has lower charged capacity. The effect of exhaustion of the low capacity cell is clearly observable. The rate of decline of the voltage increases sharply at the point 3 where the voltage undergoes a sudden drop and the rate of decline then decreases sharply at the point 4 as the voltage resumes its former slow decrease.
Sealed nickel cadmium batteries may be safely over-charged by a large amount provided that the rate of charge (and over-charge) is quite low, typically below the rate of 1/10 of the nominal capacity per hour. Fast charging at a rate of 1 nominal capacity per hour is generally considered safe provided that no cell of the battery is over-charged.
Battery processing by over-charge to equalize charged capacities of the cells of a battery (i.e. by charg
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Angilley Phillip
Young Malcolm
Seymour John York
Toatley , Jr. Gregory J.
Wong Peter S.
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