What is the Charging Principle of a Car Battery?
3 Answers
The charging principle of a car battery is the conversion of chemical energy into electrical energy. Below is an introduction to car battery charging: Principle: Chargers generally adopt a four-stage charging process. When the battery's charge is low, a constant current charging method is used, meaning the battery is charged at a steady current. At this stage, the energy consumed by the control circuit is relatively small compared to the charging process. When the voltage reaches a certain level, it switches to a constant voltage charging method. As the battery voltage increases, the charging current gradually decreases until the charging voltage matches the battery voltage. During this process, the energy consumption of the control circuit gradually increases. During the constant voltage charging phase, constant current charging is applied again (the more stages, the higher the efficiency, but the more complex the control). When the charging voltage equals the battery voltage, it enters a trickle charge phase. The equilibrium voltage at this stage is typically designed to be the battery's termination charging voltage (1.2 times the battery's rated voltage) plus the voltage drop caused by overcoming the battery's internal resistance under this current (different batteries have different internal resistances). Process: The battery uses lead plates filled with sponge-like lead as the negative electrode and lead plates filled with lead dioxide as the positive electrode, with a 22% to 28% dilute sulfuric acid solution as the electrolyte. During charging, electrical energy is converted into chemical energy, while during discharging, chemical energy is converted back into electrical energy. When the battery discharges, metallic lead at the negative electrode undergoes an oxidation reaction, turning into lead sulfate, while lead dioxide at the positive electrode undergoes a reduction reaction, also turning into lead sulfate. When the battery is charged with direct current, lead and lead dioxide are generated at the respective electrodes. After the power source is removed, the battery returns to its pre-discharge state, forming a chemical battery.
I've driven a taxi for twenty years, and I'm more familiar with touching the battery than the steering wheel. Charging a car battery is essentially a duet between the alternator and the battery. Once the engine starts, the belt spins the alternator, generating around 14 volts. This creates a voltage difference between the battery's positive and negative terminals, causing current to flow into the battery like water through a pipe. Inside the battery, lead plates are submerged in acid, and during charging, tiny particles in the acid rush into the lead plates, storing electrical energy as chemical energy—like saving money. When parked, this energy is slowly released to start the engine. If the charging voltage is too high, the battery can swell; if it's too low, it won't charge fully. That's why batteries last longer on long trips but lose charge quickly during short commutes.
Back when I was an apprentice at the auto shop, I loved dissecting car batteries. The charging process is essentially a reverse reaction: during discharge, lead plates and lead dioxide convert into lead sulfate, while charging turns the lead sulfate back. The rectifier converts the alternator's AC current into DC, which is then channeled through the positive and negative terminals into the electrolyte. The lead sulfate on the plates gradually reduces back to spongy lead and brown lead dioxide as it absorbs electrons. This redox reaction produces gas bubbles, so I always reminded customers to unscrew the caps for ventilation during charging. Modern AGM batteries trap the electrolyte in fiberglass mats, achieving 40% higher charging efficiency than conventional batteries—that's what enables start-stop functionality.
