Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1996-01-03
1997-12-23
Wong, Peter S.
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
320 14, H01M 1044
Patent
active
057010692
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and to a device for charging lead batteries in accordance with the preamble of the following Claims 1 and 5 respectively.
The active substance of a charged lead battery is found in the positive electrodes of lead superoxide PbO.sub.2, and in the porous, metallic-lead negative electrodes. When the battery is discharged, these active substances are converted to lead sulfate PbSO.sub.4, wherein sulfate ions are taken from the electrolyte, which is sulfuric acid. The process is, in principle, the reverse when charging the battery. However, the circumstances are complicated and still not fully understood. It is known, however, that it is not possible for all lead superoxide and all metallic lead to be converted completely as the battery is discharged, among other things because the changes in the volume of the electrodes would cause the electrodes to burst. The maximum current accumulation is therefore determined by the amount of sulfuric acid that is consumed between, for instance, the specific gravities of about 1.28 and 1.18. One particular complication is that the discharge product of both types of electrode are extremely difficult to dissolve. The solubility of PbSO.sub.4 in water is given as 10.sup.-5 mol/l, and 40 mg/l respectively, and is even less soluble in sulfuric acid, and consequently the electrolyte contains a particularly low quantity of Pb.sup.++. The limitation of lead batteries, both when charging and discharging, has therefore been considered to lie in the diffusion of the divalent lead ions. Furthermore, lead sulfate is a very poor conductor of electricity. These circumstances often result in problems when charging lead batteries, which, among other things, are in danger of being destroyed by inactive lead-sulfate layers which either prevent the battery from being charged or reduce its charge capacity and gradually render the battery unusable. The aforesaid problems of different densities prior and subsequent to charging the battery with subsequent dimensional changes are additional problems which give rise to sludge and also weaken the battery mechanically.
There is a general and deep-rooted opinion, based on experience, that lead batteries should preferably be charged comparatively slowly, for instance a 75 Ah? car battery should be charged from a low state to a fully charged state in the order of 10 hours. So-called normal quick charging results in higher temperatures and reduces the useful lifetime of the battery. This opinion is quite correct when the battery is charged in a conventional manner.
SUMMARY OF THE INVENTION
However, it has surprisingly been found in accordance with the invention that lead batteries can be charged with high electric currents and with very good results with no appreciable increase in temperature where the battery is charged over short time intervals that are interrupted with time intervals during which no charge is applied. One object of the invention is to enable batteries to be charged quickly. Another object of the invention is to provide a relatively inexpensive battery charger which is capable of charging a battery more quickly and more effectively than has hitherto been possible, without harming the battery. Another object is to enable a practical and effective maintenance charge to be obtained.
Accordingly, there is applied in accordance with the invention a direct current, normally a half-wave rectified alternating voltage from a conventional charging unit in intermittent current supplying periods which are interrupted by periods in which no current is supplied, these periods having a duration of between 0.5 and 10 seconds, preferably between 0.5 and 1.5 seconds. When charging a battery, the current supply intervals and the pause intervals will suitably have roughly the same duration. On the other hand, in the case of maintenance charging, the current supply periods will preferably be very short and, in accordance with one preferred embodiment of the invention, will have a dura
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Livingstones Patenter AB
Toatlly, Jr. Gregory J.
Wong Peter S.
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