Battery protection system

Claim 1

In an engine-driven system having an engine, a storage battery to provide starting power for the engine, charging means connected to the battery and driven by the engine to provide charging current for the battery when the engine is running, an ignition switch having a first condition in which the engine is operative and a second condition in which the engine is inoperative, and a load circuit connected to the battery to receive electrical power from the battery, a battery protection system to protect the battery from being discharged below a predetermined minimum value sufficient to start the engine, said protection system comprising: (a) a protection circuit comprising: (i) a stable voltage source, (ii) a comparator connected to the stable voltage source and to the battery to compare voltage derived from the battery with voltage derived from the stable voltage source, (iii) controllable switching means connected in series with the load circuit to disconnect the load circuit from the battery when the battery voltage decreases below a predetermined value, (iv) a latchable switching means comprising: (1) a fixed contact; (2) a movable contact; (3) setting means connected to a charge-measuring means to be controlled thereby to move the movable contact into conductive connection with the fixed contact only when the value functionally related to the charge remaining in the battery is below the predetermined value sufficient to start the engine; 4) resetting means connected to the ignition switch to be energized thereby to move the movable contact out of conductive connection with the fixed contact when the ignition switch is in its first condition; and b) actuating means connected to the protection circuit and to the ignition switch to actuate the protection circuit when the ignition switch is in its second condition, to disconnect the load circuit from the battery when the value functionally related to the charge remaining in the battery decreases below a predetermined value sufficient to start the engine, said actuating means comprising a coil connected in series with the battery and the ignition switch being energized only when the ignition switch is in its first condition, said coil being operatively connected to normally closed contacts conductively connected to each other only when the ignition switch is in its second condition and electrically separated from each other when the ignition switch is in its first condition, the normally closed contacts being connected in series with the battery and the protection circuit to require the protection circuit to operate when the ignition switch is in its second condition and to prevent the protection circuit from operating when the ignition switch is in its first condition.