Definition
The voltage level at which an energized electromagnetic device, such as a relay or solenoid, releases and returns to its de-energized position. As voltage applied to the coil decreases, drop-out voltage is the specific value at which the magnetic field becomes too weak to hold the armature, and spring tension pulls the contacts open.
Plain English
It is the voltage at which a relay or solenoid lets go and switches off. Above that voltage, the magnet inside is strong enough to hold it closed. Below it, the spring wins and it pops back open.
Context Anchor
Seen in aircraft electrical system descriptions, component specifications, and troubleshooting for relays, solenoids, contactors, and voltage-controlled devices.
Derivation
"Drop-out" comes from the physical action of the relay's armature dropping away from the electromagnet when the coil no longer has enough voltage to hold it. The name describes exactly what happens inside the device.
Why Pilots Care
Low battery voltage can cause relays to drop out, disabling starter circuits, avionics, or other essential systems during flight or ground operations.
Intuition Check
Drop-out voltage does not mean zero voltage. It means the voltage has fallen low enough that the device can no longer stay held on.
Example Sentence 1
The technician measured the relay's drop-out voltage to confirm it was still within the manufacturer's specification.
Example Sentence 2
Technicians checked the drop-out voltage of the master relay during the preflight electrical inspection.