The document discusses the challenges of fast charging Nickel-Cadmium (NiCd) batteries, specifically regarding battery heating and voltage monitoring limitations. It proposes a solution based on measuring cell surface temperature relative to ambient temperature to taper the charge current as the battery reaches full capacity.
Two primary circuit designs are presented: a practical thermally controlled charger using an LT1006 amplifier and Type K thermocouples, and a switched-mode version utilizing a duty cycle modulator. The note also includes construction details for low-resistance shunts required to measure high charging currents accurately.
The circuit detects full charge by measuring cell surface temperature relative to ambient; when the battery is saturated, it produces heat that raises its temperature above the ambient level.
The circuit values provided in the document limit the battery surface temperature rise over ambient to about 15 degrees Celsius.