A battery charging circuit, which can charge storage batteries upto the required voltage level, and prevent them from being overcharged by use of a thyristor, a temperature sensor and a current regulation means. The circuit uses a regulated switched B.sup.+ supply which is controlled by a transistor which is switched on and off by control of the thyristor. The circuit of the present invention consequently can protect not only the storage batteries themselves, but also the electronic circuits and instruments, which use the storage batteries as their power sources, from being damaged due to overcharging.
A battery pack containing a rechargeable battery is detachable to a charger unit for charging under the control of a charging circuit in the charger unit. The battery pack includes a sensor output circuit which comprises a temperature sensor for sensing the temperature of the battery being charged. A voltage dividing resistor network is formed in the sensor output circuit and receives a constant current from the charging circuit upon attachment of the battery pack to the charger unit such that it provides an enable signal of a first voltage level to the charging circuit for allowing the charging of the battery at a first charge rate so long as the sensed battery temperature is below a predetermined reference level. When the sensed battery temperature exceeds the reference level, the voltage dividing resistor network responds to provide a stop signal of a second voltage level for inhibiting the charging at the first charge rate. Also included in the sensor output circuit is a hold circuit which holds to provide the stop signal to the charging circuit once the sensed temperature exceeds the reference level.
A lockout circuit is provided in a battery pack (10) which blocks charging by incompatible chargers while allowing charging by a compatible charger (12). The battery comprises a battery cell or cells (22), and a switch circuit (24). The switch circuit blocks charge current until a switch disable signal is provided to a switch disable contact (18). The switch circuit provides a one way bypass so that the battery may provide power to a device. To eliminate voltage drop while powering a device, a current sense circuit is provided to detect discharge current, and disable the switch circuit.
The present invention discloses a thermal protection device which includes a temperature limiting switch such as a thermostat to switch off a charging loop to a rechargeable battery to prevent overheating in the cells of the rechargeable battery. The thermal protection device further includes a parallel loop for continuously conducting a discharging current when the charging loop is switched off. The parallel loop include a diode which allows current to flow only in the opposite direction of the charging current through the temperature limiting switch. The power output from the rechargeable batteries is therefore not affected by the switching on and off of the temperature limiting switch for controlling the charging operations.
A battery charging circuit is provided with a thermally controlled cut-off switch whose normally closed contacts are in series with the main terminals of a thyristor. The thyristor is switched ON on commencement of battery charging by the charging of a capacitor C1, which remains charged even when the contacts of the cut-off switch open as a result of the battery temperature rising upon completion of charging. Consequently, the thyristor remains latched OFF by the capacitor even when the contacts of the cut-off switch close, and can only be turned ON again by disconnecting the battery or power supply, disconnection of the battery or power supply causing capacitor C1 to discharge through a charge maintenance by-pass circuit connected in parallel with the thermal switch and thyristor.
An overcharge protection circuit for a battery pack and a method of recharging a battery pack in which a charging adaptor having two charging terminals may be used for a metal hydride battery pack, or the like, despite the fact that such a charging adaptor is responsive to a detected change in voltage across the two battery pack terminals to terminate a high rate of charging. The overcharge protection circuit senses the temperature of the cells in the battery pack and, when the sensed cell temperature reaches a threshold temperature, adjusts the voltage appearing across the battery pack terminals to exceed the change in voltage to which the charging adaptor responds by terminating a high rate of charging.
