Project 19 - SELF-REGULATING BATTERY CHARGER

Abstract

This chapter focuses on the self-regulating battery charger. This self-regulating device charges a 12V car battery at a rate of 3A to 4A when the accumulator is “flat,” but then automatically reduces the charge to a trickle rate when the battery voltage reaches its “fully charged” value. Thus, the unit eliminates the danger of overcharging a battery, and eliminates the need for the owner to occasionally check the battery state when it is connected to the charger. If a battery is permanently connected to the charger, it will automatically be maintained in a permanent state of full charge, but will never be overcharged. The full circuit of the charger is shown diagrammatically in the chapter. Transformer T1 and bridge rectifier D1–D4 step down and rectify the mains line voltage, and apply a charge current to the battery via limiting resistor R1 and silicon controlled-rectifier SCR1. When setting up and using the charger, it may be found that, instead of the charge rate falling abruptly from full to trickle as the battery reaches full charge, the charge current falls briefly from full rate to half rate, and then falls to trickle rate some time later.