Title: Battery charging circuit

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Abstract: A battery charging circuit is provided where a synchronous switch, such as a magnetic amplifier, saturable reactor, silicon controlled rectifier, triac or contactor, each of which is controllable, is inserted in a charging circuit and is controlled by a circuit such that when the terminal voltage of a battery which is being charged by a substantially constant, ripple-free DC current reaches a predetermined level, an intermittent DC charge is initiated. The periods of operation are of a predetermined, fixed length and at a predetermined current level. Means may be provided to reduce the finish charge to an intermittent trickle charge when the terminal voltage of the battery reaches its rated level. Counting means can be provided for determining the number of periods of operation of intermittent charging current delivered to the battery, for surveillance of battery condition and so as to determine ampere-hour back charge. The control circuit is arranged so as to be fail safe, by insertion of a current level bias control element in series in the control circuit for the synchronous switch, with the knowledge that such bias control elements fail "open". Thus, no override protection devices are required. The method of charging the battery includes supplying a constant, substantially ripple-free DC charging current until the battery terminal voltage reaches a predetermined level, and then initiating an intermittent DC charging current while continuously sensing the battery terminal voltage.


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