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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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As compared to constant-current system, the constant-voltage system of charging a lead acid cell has the advantage of
reducing time of charging
increasing cell capacity
both (a) and (b)
avoiding excessive gassing
both (a) and (b)
Quick Summary: The constant-voltage charging method maintains a fixed potential across the lead-acid battery terminals throughout the process. As the battery internal EMF increases towards the charger voltage, the charging current naturally tapers off, which allows for faster initial charging while effectively utilizing the chemical capacity of the plates.
The constant-voltage charging method maintains a fixed potential across the lead-acid battery terminals throughout the process. As the battery internal EMF increases towards the charger voltage, the charging current naturally tapers off, which allows for faster initial charging while effectively utilizing the chemical capacity of the plates.
I=RV−E — Current flow relation where V is charger voltage, E is battery EMF, and R is internal resistance.
In a constant-voltage system, the charging current I is governed by the equation I=RinternalVcharger−Ebattery. Initially, when the battery voltage Ebattery is low, the current is high, allowing rapid energy storage. As the battery approaches full charge, Ebattery rises, causing I to decrease automatically, which helps in deep plate saturation (increasing effective capacity) and prevents excessive electrode deterioration.
Constant-voltage charging provides a high initial charging rate.
The current tapers down as the battery reaches full state-of-charge.
This method is widely used in automotive charging systems and stationary power backups.
Reduces the risk of thermal runaway compared to poorly managed constant-current sources.
Significantly faster charging time during the initial phase.
Better utilization of plate material leading to higher effective capacity.
Requires less supervision as the current decreases automatically.
High initial current can damage a completely flat/sulfated battery.
Requires stable voltage regulation to avoid overcharging at the end of the cycle.
Automotive vehicle alternators.
UPS and emergency lighting power supplies.
Telecommunication battery banks.
| Feature | Constant-Voltage | Constant-Current |
|---|---|---|
Current behavior | Decreases over time | Remains constant |
Constant-current charging is primarily used for formation of plates during manufacturing or specific equalization charges.
Option D is incorrect because while constant-voltage helps, it is not the primary advantage compared to time/capacity gains; excessive gassing is actually a risk if the constant voltage is set too high.
C is correct — The constant-voltage method reduces charging time due to high initial current and improves capacity utilization by allowing deeper saturation of the active material as current tapers.
Always remember that in electrical machines and batteries, 'Constant Voltage' usually implies a self-regulating or tapering mechanism, whereas 'Constant Current' requires active feedback control.