Lead-acid-battery-charger

This circuit provides an initial voltage of 2.5 V per cell at 25°C to rapidly charge a battery. The charging current decreases as the battery charges, and when the current drops to 180 mA, the charging circuit reduces the output voltage to 2.35 V per cell, leaving the battery in a fully charged state. This lower voltage prevents the battery from overcharging, which would shorten its life. The LM301A compares the voltage drop across R1 with an 18 mV reference set by R2. The comparator's output controls the voltage regulator, forcing it to produce the lower float voltage when the battery charging current, passing through R1, drops below 180 mA. The 150 mV difference between the charge and float voltages is set by the ratio of R3 to R4. The LEDs indicate the state of the circuit. Temperature compensation helps prevent overcharging, particularly when a battery experiences wide temperature changes while being charged. The LM334 temperature sensor should be placed near or on the battery to decrease the charging voltage by 4 mV/°C for each cell. Because batteries require more temperature compensation at lower temperatures, R5 should be changed to 30 Ω for a temperature coefficient of -5 mV/°C per cell if the application will encounter temperatures below -20°C. The charger’s input voltage must be filtered to ensure it is at least 3 V higher than the maximum required output voltage, which is approximately 2.5 V per cell. Select a regulator based on the maximum current needed: LM371 for 2 A, LM350 for 4 A, or LM338 for 8 A. At 25°C and with no output load, adjust R7 for a Vout of 7.05 V and adjust R8 for a Vout of 14.1 V.

This charging circuit is designed to efficiently manage the charging process of a battery while ensuring its longevity and safety. The initial voltage of 2.5 V per cell is optimized for rapid charging, allowing the battery to reach its capacity quickly. As the battery approaches a full charge, the current diminishes, triggering a transition to a float voltage of 2.35 V per cell. This mechanism is crucial as it prevents overcharging, a condition that can lead to battery degradation.

The LM301A operational amplifier acts as a voltage comparator, monitoring the voltage across a shunt resistor (R1). When the charging current falls below 180 mA, a predetermined threshold, the output of the LM301A changes state, signaling the voltage regulator to switch to the lower float voltage. The reference voltage for this comparator is established by R2, which is set to 18 mV. The difference between the charging and float voltages is carefully controlled through the resistor network formed by R3 and R4, ensuring that the transition between charging and float states is smooth and precise.

LED indicators provide visual feedback regarding the operational status of the circuit, allowing users to easily monitor the charging process. The inclusion of temperature compensation through the LM334 temperature sensor is a significant feature, as it adjusts the charging voltage in response to temperature variations. This adjustment is particularly important in environments where the battery may be exposed to extreme temperatures, thus ensuring safe charging conditions.

For applications in colder environments, modifying R5 to 30 Ω allows for an additional temperature compensation factor, further safeguarding the battery from potential overcharging risks. The design stipulates that the input voltage must be at least 3 V above the maximum output voltage to maintain proper regulation. This ensures that the voltage regulator can effectively manage the output under varying load conditions.

Selecting the appropriate voltage regulator is critical and should be based on the maximum current requirements of the application. The LM371, LM350, and LM338 regulators provide options for different current capacities, ensuring versatility in design. Fine-tuning of resistors R7 and R8 at a no-load condition allows for precise output voltage settings, ensuring the circuit operates within specified parameters. Overall, this circuit provides a robust solution for battery charging with built-in protections and operational flexibility.This circuit furnishes an initial voltage of 2.5 V per cell at 25° C to rapidly charge a battery. The charging current decreases as the battery charges, and when the current drops to 180 mA, the charging circuit reduces the output voltage to 2.35 V per cell, leaving the battery in a fully charged state. This lower voltage prevents the battery from overcharging, which would shorten its life. The LM301A compares the voltage drop across R1 with an18 mV reference set by R2. The comparator"s output controls the voltage regulator, forcing it to produce the lower float voltage when the batterycharging current, passing through R1, drops below 180 mA.

The 150 mV difference between the charge and float voltages is set by the ratio of R3 to R4. The LEDs show the state of the circuit. Temperature compensation helpsprevent overcharging, particularly when a battery undergoes wide temperature changes while being charged. The LM334 temperature sensor should be placed near or on the battery to decrease the charging voltage by 4 mV/°C for each cell.

Because batteries need more temperature compensation atlower temperatures, change R5 to 30 0 for a tc of -5 mV/°C per cell if application will see temperatures below -20°C. The charger"s input voltage must be filtered de that is at least 3 V higher than the maximum required output voltage: approximately 2.5 V per cell.

Choose a regulator for the maximum current needed: LM371 for 2 A, LM350 for 4 A, or LM338 for 8 A. At 25°C and with no output load, adjust R7 for a VouT of 7.05 V, and adjust R8 for a Vom of 14.1 V. 🔗 External reference