Method and apparatus for charging a lead acid battery

Abstract

A battery charger for a lead acid battery having a power supply with an input connected to an AC signal and an output connected to the battery. The power supply provides a charge current to the battery. A clock connected to the AC signal provides clock pulses having transitions synchronized with zero crossings of the AC signal. A voltage monitor connected to the battery detects a battery voltage substantially simultaneously with a zero value of the charge current. A charge mode control is connected to the clock and the voltage monitor for commanding different battery charge currents. The voltage monitor includes a temperature compensation circuit. The battery charger includes a display module that can be placed at a location remote from the battery charger and convenient to the user. The battery charger executes a battery charge cycle in which absorption and equalization charge times are variable and automatically set as a function of the state of discharge of the battery, that is, as a function of the bulk charge time. During an initial evaluation period, the battery is tested for a deep discharge condition, and if detected, a desulfation charge current is automatically applied for a time period, for example, two hours.