Class 4 (4th Engineer) MET 📅 Feb 2023

Exam Question

(a) Compare constant current method and constant voltage method of charging batteries (6)

(b) A 24V emergency battery is to be charged from the 110V ship' mains when the e.m.f per cell has fallen to a minimum value of 1.8V. The battery consists of 12 cells in series, has a capacity of 100Ahr at a 10 hr rate and the internal resistance is 0.03Ω/cell. If charging continues until the voltage per cell rises to 2.2V, find the values of the variable resistor needed to control the charging. The charging current can be assumed to be equal to the maximum allowable discharge current (10)

Reference Answer

### (a) Comparison of Constant Current and Constant Voltage Charging Methods
A detailed comparison between the Constant Current (CC) and Constant Voltage (CV) methods for charging lead-acid batteries is as follows:
#### Constant Current (CC) Method
* **Principle:** The charging current is maintained at a constant, predetermined level throughout the charging process. As the battery's state of charge increases, its back EMF rises, requiring the external charging voltage to be progressively increased to maintain the constant current.

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