Monitoring bus voltage vs. alternator voltage (?)

[Brian Vickers]

I like warning lights and alarms that tell me when something is malfunctioning. My Plane Power alternator installation diagram shows a simple alternator out light alternative. Aeroelectric Figure Z-11 shows the use of a low voltage monitor module. I purchased the unit and it actually has an over voltage alarm limit as well. My understanding is that the Plane Power system monitors only the alternator. The B&C unit is connected to the bus and therefore monitors bus voltage. Does this mean when the alternator voltage drops, the B&C unit will not be activated until the battery is depleted below the monitor's preset limit? In other words, the warning light will not trip while the battery is fully charged. I want to know the moment the alternator goes above or below normal operating limits.

[vic syracuse]

Brian, I have the B&C regulator with the built-in low voltage warning, and it is just that---- it comes on when bus voltage is below about 12.3-12.5 volts, which usually means the alternator has failed. That usually happens within a couple of seconds of an alternator failure with a typical load. In flight I usually show a steady state current of 18-25 amps in the daytime, so the battery will quickly drop to 12.5 or less rather quickly once the alternator is offline.

Vic