--- title: "Battery charger circuit and charging methods" subject: "Industrial Power Distribution and Illumination" chapter: 9 key: "semester_6/industrial_power_distribution_and_illumination:battery-charger-two-methods" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/battery-charger-two-methods site: BCT Engineering --- # Battery charger circuit and charging methods Industrial Power Distribution and Illumination · Chapter 9: Emergency and Backup Supply Systems - Asked in: 2078 Chaitra, 4+4 marks - Video: [Battery Charger (Basics, Circuit, Working, Applications, Block Diagram, Pros & Cons) Explained](https://www.youtube.com/watch?v=6v0p8gEi3MQ) — Engineering Funda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/battery-charger-two-methods - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-9 ## Question Explain battery Charger with neat sketch circuit diagram. Explain any two methods for battery charging system. ## Short answer A battery charger converts AC to controlled DC via transformer, rectifier, filter, and regulator to restore battery energy. Constant-current charging holds current steady (≈1/10 Ah rating) while voltage rises; constant-voltage charging applies fixed voltage (2.3-2.4 V/cell) with current tapering as battery charges. ## Answer #### Battery charger A **battery charger** converts AC mains into controlled DC and drives current into a secondary battery in the direction opposite to discharge, restoring its chemical energy. A typical single-phase charger has: 1. **Step-down transformer** – reduces 230 V to a suitable level and isolates the battery from mains. 2. **Rectifier** – bridge of diodes or thyristors (SCRs) to convert AC to DC. 3. **Filter/choke** – smooths the DC current. 4. **Regulator/control** – series resistance, SCR phase control or switch-mode regulator to set constant current or constant voltage. 5. **Protection and metering** – fuse/MCB, reverse-polarity diode, ammeter, voltmeter, overcharge cut-off. ```text 230 V ─►[Fuse]─►[Step-down ]─►[Bridge ]─►[Choke/ ]─┐ AC [transformer] [rectifier] [regul. ] │ (A) │ ┌──(V)──┐ │ └─+Batt−┘◄────────┘ ``` The SCR-controlled version measures battery voltage and current and adjusts the firing angle to give the required charging profile. #### Method 1: Constant-current charging - The charging current is held constant (about 1/10 of the Ah rating, e.g. 10 A for 100 Ah) by adjusting a series resistance or the rectifier output while battery voltage rises from about 2.0 to 2.6 V/cell. - Charging time ≈ Ah to be restored / current, plus about 10–20% for losses. - **Two-rate** variant: high current until gassing begins (~2.4 V/cell), then a lower finishing rate. - Advantages: simple, accurate control of charge given. Disadvantage: slow; overcharge and gassing if not stopped. #### Method 2: Constant-voltage charging - A constant voltage of about 2.3–2.4 V per cell is applied. At first the current is high because the battery EMF is low; it falls automatically as the EMF rises, approaching a small value at full charge. - A current-limit resistor or electronic limit protects against the initial surge. - Advantages: faster charging (about 80% in a few hours), less risk of overcharging, no supervision. - Used in automobiles and modern CC–CV chargers. ```text Const. current Const. voltage I │──────┐ I │\ │ │ │ \__ │ └─ t │ ‾‾───── t ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the role of the step-down transformer in a charger? A. Reduces 230 V to a suitable level and isolates the battery from mains B. Smooths the DC current C. Converts AC to DC D. Cuts off at overcharge Answer: A. The rectifier converts, the filter smooths, and the transformer steps down and isolates. (Key point: Charger parts) 2. How does an SCR-controlled charger set the charging profile? A. It switches resistors manually B. It senses battery voltage and current and adjusts the firing angle C. It changes the mains frequency D. It fixes the firing angle at 0 Answer: B. Phase control varies rectifier output as required. (Key point: SCR charger) 3. What are the features of constant-current charging? A. Voltage fixed, current falls; fast B. Tiny current for idle battery C. Current is held at about C/10 while voltage rises; simple but slow and risks overcharge D. Current doubles near the end Answer: C. The two-rate variant reduces current once gassing starts at ~2.4 V/cell. (Key point: Constant-current charging) 4. What happens in constant-voltage charging at 2.3-2.4 V/cell? A. Current stays constant B. Current rises with time C. It is slower and needs supervision D. Current is high at first and falls as EMF rises, so it needs little supervision Answer: D. A current limit protects against the initial surge. (Key point: Constant-voltage charging) ## Related in Industrial Power Distribution and Illumination - [Types of battery charging system](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Abattery-charging-system-types) — Industrial Power Distribution and Illumination, chapter 9, asked 3× - [Charging lead acid battery from AC source](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Alead-acid-ac-charger) — Industrial Power Distribution and Illumination, chapter 9 - [Battery charging schemes and most effective](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Abattery-charging-schemes-effective) — Industrial Power Distribution and Illumination, chapter 9 - [Trickle charging and Ah/Wh efficiency (4 A, 12 h, 1.2 V)](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Atrickle-charging-4a-1-2v) — Industrial Power Distribution and Illumination, chapter 9, asked 3× - [Trickle charging and Ah/Wh efficiency (2.2 V, 2.44 V)](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Atrickle-charging-2-2v) — Industrial Power Distribution and Illumination, chapter 9, asked 3× - [Trickle charging and Ah/Wh efficiency (30 A, 6 h)](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Atrickle-charging-30a-6h) — Industrial Power Distribution and Illumination, chapter 9, asked 2× ## Related in other subjects - [Battery charger bridge 15 V: currents, power, efficiency](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Abattery-bridge-15v-efficiency) — Power Electronics, chapter 2, asked 3× - [Battery charger bridge: average current, efficiency](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Abattery-bridge-30v-avg-efficiency) — Power Electronics, chapter 2 - [Battery charger bridge 30 V: conduction period](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Abattery-bridge-30v-conduction) — Power Electronics, chapter 2, asked 4× - [Battery charger bridge 30 V: conduction, power](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Abattery-bridge-30v-conduction-power) — Power Electronics, chapter 2, asked 2×