FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsMedium
A technician connects two 12-volt, 20 ampere-hour batteries in series to supply a 24-volt DC bus. What is the resulting voltage and capacity of the combined battery pack?
- A24 volts and 40 ampere-hours
- B24 volts and 20 ampere-hours
- C12 volts and 40 ampere-hours
- D12 volts and 20 ampere-hours
Show answer & explanationAnswer & explanation
Correct answer: B. 24 volts and 20 ampere-hours
Connecting batteries in series adds their voltages (12V + 12V = 24V) while the ampere-hour capacity remains the same as a single battery (20 Ah), since the same current flows through both batteries in a series path.
Why the other options are wrong
- A. Capacity does not double in a series connection; only voltage adds.
- C. This describes a parallel connection's voltage combined with a doubled capacity, which doesn't apply here.
- D. Voltage doubles in series, so 12 volts is incorrect for this configuration.
Series vs Parallel Battery Wiring
Wiring batteries in series adds voltage while capacity stays the same; wiring in parallel keeps voltage the same while capacity adds.
- Series: voltages add, capacity (Ah) unchanged
- Parallel: voltage unchanged, capacity (Ah) adds
- Same current flows through series-connected batteries
Memory trick: Series stacks Volts; Parallel pools Amps.