GROL Power Sources and Distribution 3 — Questions and Answers
Question 1: What is the nominal voltage of a single cell in a fully charged lead-acid battery?
- 1.2 volts per cell
- 1.5 volts per cell
- 2.0 volts per cell (Correct answer)
- 3.7 volts per cell
Correct answer: 2.0 volts per cell
Each cell of a fully charged lead-acid battery has a nominal voltage of approximately 2.0 volts, so a 12V battery contains six cells in series.
Question 2: What is the primary operational advantage of lithium-ion batteries over lead-acid batteries in marine applications?
- Higher energy density and significantly lighter weight for the same capacity (Correct answer)
- Lower initial purchase and replacement cost
- Superior performance in subfreezing temperatures
- Complete elimination of fire and thermal runaway risk
Correct answer: Higher energy density and significantly lighter weight for the same capacity
Lithium-ion batteries store significantly more energy per pound than lead-acid, making them ideal for weight-sensitive marine installations.
Question 3: Which charging method is specifically recommended for nickel-cadmium (NiCd) batteries to prevent overcharging damage?
- Constant voltage charging with a high cutoff threshold
- Trickle charging at C/100 rate indefinitely
- Pulse-width modulation with periodic rest intervals
- Constant current charging with a reliable termination method (Correct answer)
Correct answer: Constant current charging with a reliable termination method
NiCd batteries require constant current (CC) charging because their relatively flat discharge curve makes voltage-based termination unreliable.
Question 4: When using a hydrometer to check a lead-acid battery, what specific gravity reading indicates a fully charged cell?
- 1.000 to 1.050 (near pure water, fully discharged)
- 1.100 to 1.150 (lightly charged)
- 1.265 to 1.285 (fully charged) (Correct answer)
- 1.350 to 1.400 (would indicate overcharge)
Correct answer: 1.265 to 1.285 (fully charged)
A fully charged lead-acid battery cell has electrolyte with a specific gravity of approximately 1.265 to 1.285.
Question 5: What is the primary purpose of applying a periodic equalization charge to a flooded lead-acid battery bank?
- Balancing cell voltages and dissolving early-stage lead sulfate crystal buildup (Correct answer)
- Rapidly restoring the battery bank to full charge after heavy discharge
- Determining the true remaining capacity of the battery bank
- Eliminating hydrogen gas produced during normal charging cycles
Correct answer: Balancing cell voltages and dissolving early-stage lead sulfate crystal buildup
Equalization applies a controlled overcharge that balances individual cell voltages and reverses early sulfation, extending overall battery life.
Question 6: In a marine system with two battery banks, what device allows both banks to be charged simultaneously from one alternator while preventing the discharged bank from draining the charged one?
- A bidirectional DC-DC converter
- A high-current solenoid relay switch
- A battery isolator using diodes or MOSFETs (Correct answer)
- A master battery disconnect switch
Correct answer: A battery isolator using diodes or MOSFETs
A battery isolator uses diodes or MOSFETs to allow only unidirectional current flow, enabling simultaneous charging while preventing inter-bank discharge.
Question 7: What storage condition is the primary cause of sulfation (hardening of lead sulfate crystals) in lead-acid batteries?
- Storing a fully charged battery at temperatures above 80°F
- Repeatedly overcharging the battery at excessive voltage
- Using distilled water for electrolyte top-up instead of battery acid
- Leaving the battery in a discharged or partially discharged state for extended periods (Correct answer)
Correct answer: Leaving the battery in a discharged or partially discharged state for extended periods
When a lead-acid battery remains discharged, lead sulfate on the plates gradually crystallizes into a hard form that resists normal recharging.
GROL Power Sources and Distribution 3
What is the nominal voltage of a single cell in a fully charged lead-acid battery?