Aircraft Electrical Systems Flashcards

What is the primary hazard associated with a nickel-cadmium battery that is charged with excessive current at high temperature?

Answer: Thermal runaway

Rising temperature lowers internal resistance in a NiCd cell, so it draws more current and heats further until thermal runaway occurs.

How is the state of charge of a nickel-cadmium battery determined?

Answer: It cannot be determined accurately by specific gravity; a measured discharge or charge is required

NiCd electrolyte specific gravity does not change appreciably with charge, so a hydrometer cannot indicate state of charge.

Why should tools and equipment used to service lead-acid batteries never be used on nickel-cadmium batteries?

Answer: The sulfuric acid can contaminate and damage the alkaline NiCd electrolyte

Acid residue will neutralize and contaminate the potassium hydroxide electrolyte and ruin NiCd cells.

When the voltage of a fully charged 24-volt lead-acid aircraft battery is measured, approximately how many cells does it contain?

Answer: 12

Each lead-acid cell produces about 2.1 volts, so a 24-volt battery has 12 cells.

What is the purpose of a battery vent system with a sump jar containing a bicarbonate of soda pad on a lead-acid installation?

Answer: To neutralize acid fumes before they are discharged overboard

The sump jar neutralizes corrosive acid vapors so they do not damage the aircraft structure.

A constant-current battery charger is used on an aircraft battery. Which statement is correct?

Answer: Charging current must be monitored and the charge stopped to prevent overcharging

A constant-current charger does not taper, so the charge must be monitored and terminated to avoid gassing and overcharge.

What is the most likely result of installing a battery with its cell vent caps not properly secured?

Answer: Spilled electrolyte causing corrosion of surrounding structure

Loose vent caps allow electrolyte spillage, which corrodes the battery box and nearby structure.