Definition
A cockpit instrument that shows the flow of electrical current, in amperes, between the alternator (or generator) and the battery. A positive reading means the alternator is charging the battery; a negative reading means the battery is discharging because it is supplying the electrical load on its own.
Plain English
A small gauge that tells you whether your aircraft's electrical system is charging the battery or draining it.
Context Anchor
Seen during engine starting and after-start checks, when the pilot confirms that the airplane’s electrical system is working normally.
Derivation
From 'ampere' (the unit of electrical current, named after French physicist André-Marie Ampère) plus '-meter' (a device that measures). Literally, a meter that measures amperes.
Why Pilots Care
Confirms the alternator or generator is recharging the battery after engine start and prevents in-flight battery failure.
Intuition Check
An ammeter is not the same as a voltmeter. A voltmeter shows electrical pressure; an ammeter shows electrical flow.
Example Sentence 1
After starting the engine, the pilot checked the ammeter and saw a positive reading, confirming the alternator was charging the battery.
Example Sentence 2
In cruise the ammeter read zero, showing the electrical load was balanced and the battery was neither charging nor discharging.