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Battery Charger

Figure 1 illustrates a temperature compensated battery charger for applications with lead acid batteries. Diode D1, placed between the power supply and battery, blocks current from flowing from the battery to the power supply. This eliminates any loading on the battery when the power supply is off, but more importantly, prevents the battery from charging the power supply’s output capacitors. With deployment of diode D1, remote sensing should be applied across the battery terminals to compensate for the diode drop. By setting the voltage and current to the bulk charge voltage and maximum charge current, the power supply will initially charge the batteries in current mode control and then automatically crossover to voltage mode control when the batteries reach the desired set point. The power supply can be programmed for time dependent, sequential step operation to equalize and float charge the batteries after bulk charging. Equalization is generally not required for every charge cycle. Table 1 illustrates the different charging steps and Table 2 provides the recommended charging voltage per cell for different battery technologies.

Caution: All battery parameters presented in this section are guidelines and the user should refer to and use manufacturer’s specifications in any battery charging application.

A temperature detector can be applied to the modulation input to adjust the set point voltage with temperature. In this example, the temperature sensor, integrated circuit U1, is a two terminal device that produces a current proportional to temperature. This device, AD592, is manufactured by Analog Devices. The temperature detector is placed in series with resistor R1 and the temperature dependent voltage is measured between terminals 25 and 1,2, or 20 of connector JS1. Table 3 provides the recommended charge voltage deviation per cell as a function of temperature. Table 4 defines the modulation parameters for applying temperature compensation to a standard 12 V lead acid battery using a PQD16-200 power supply. The modulation control parameter should be set to voltage control and modulation type should be set to 1.

Figure 1. Battery Charger with Temperature Compensation

Table 1. Charging Programming and Characteristics

Table 2. Battery Charging Per Cell

Table 3. Battery Charging Temperature Compensation per Cell

Table 4. Modulation Table for Temperature Compensated Battery Charger (Type 1)