Battery charging system

Claim 1

A battery charging system for charging batteries on demand and operative to prevent continued charging current passage when the battery is fully charged, said system comprising: rectifying means adapted to receive an A.C. signal and convert the same to a D.C. signal; means connected to said rectifying means and adapted to be connected to a battery for conducting said D.C. signal to a battery; battery charge regulating means including electronic switch means in said conducting means and operative when on to permit the passage of current to a battery and when off to preclude passage of current to a battery; and means across said conducting means and arranged to by pass a battery connected thereto for sensing the voltage to be applied to the battery and for turning said electronic switch means off whenever the voltage exceeds that corresponding to a desired maximum charge to thereby preclude vaporization of battery electrolyte which would result in a decrease in the energy storage capacity of the battery and yet insure the maintenance of a desired maximum charge on the battery; said conducting means comprising a pair of electrical conductors, said switch means comprising a transistor in one of said conductors, and said sensing means comprising a voltage divider across said conductors and biasing means for said voltage divider, said biasing means comprising a second transistor and a resistor serially connected across said conductors between said rectifier and said first transistor, a third transistor having its base connected to the junction of said second transistor and said resistor and its collector-emitter circuit serially connected with a capacitor across said conductors, the common junction of said third transistor and said capacitor being connected to the base of said first transistor, said voltage divider being connected to the base of said second transistor.