Battery Charging System with Overload Protection - Electrical Engineering Guide
1. Introduction
A Battery Charging System with Overload Protection is designed to charge batteries efficiently while preventing damage due to overcurrent or overload conditions. This ensures safe operation and extended battery life.
2. Objectives
• Efficient battery charging
• Prevent overcharging and overloading
• Automatic cutoff under fault conditions
3. System Overview
The system monitors the charging current and voltage. When overload conditions are detected, the system disconnects the charging circuit to protect the battery and the components.
4. Components Required
• Step-down transformer
• Bridge rectifier
• Voltage regulators (LM317, LM7812, etc.)
• Microcontroller (e.g., ATmega328, optional)
• Current and voltage sensors (ACS712, voltage divider)
• Relay or MOSFET switch
• Battery (Lead-acid or Li-ion)
• Heat sinks, fuses, LEDs, connectors
5. Block Diagram and Working Principle
The block diagram includes a transformer, rectifier, voltage regulator, control unit (microcontroller), and protection circuitry. The system senses current and voltage; if overload is detected, it activates a cutoff mechanism.
6. Circuit Design and Schematic
Design includes rectification, voltage regulation, current sensing, and switching circuit using relay/MOSFET. The microcontroller monitors voltage and current levels using ADC.
7. Battery Charging Algorithm
• Constant current (CC) phase until battery voltage reaches
threshold
• Constant voltage (CV) phase to top off the battery
• Automatic cutoff after full charge or timer-based logic
8. Overload Protection Mechanism
Use a current sensor to measure real-time load. If the current exceeds a defined threshold, trigger a relay or MOSFET to disconnect the battery from the charging circuit.
9. Power Supply Design
Use a transformer to step down AC voltage followed by a bridge rectifier and capacitive filter. Voltage regulators ensure steady DC output for logic and charging circuits.
10. Implementation Steps
1. Assemble rectifier and regulator circuit
2. Add voltage/current sensing module
3. Program microcontroller for monitoring
4. Implement cutoff mechanism
5. Calibrate thresholds and test charging
11. Safety Considerations
• Use appropriate fuse rating
• Ensure proper heat dissipation
• Use opto-isolators for relay drivers
• Insulate high-voltage sections properly
12. Testing and Calibration
Test using different battery levels and simulate overload using variable loads. Check for proper voltage regulation and timely disconnection during overload.
13. Applications
• Battery charging stations
• Uninterruptible power supplies (UPS)
• Solar-powered battery banks
• Electric vehicle (EV) battery chargers
14. Advantages and Limitations
Advantages:
• Safe charging
• Overload protection
• Automation possible
Limitations:
• Requires calibration
• Slightly increased complexity
• Sensor cost
15. Cost Estimation
• Transformer and rectifier: $15–$25
• Voltage regulator and control: $10–$20
• Sensors and protection: $10–$15
• Total: $35–$60
16. Future Enhancements
• Add LCD or mobile interface for real-time monitoring
• Use MPPT for solar-based systems
• Add temperature-based protection
• Wireless alert on fault
17. Conclusion
This project ensures safe and efficient battery charging. Overload protection adds reliability and prolongs the battery's lifespan. It’s useful for home and industrial power applications.