What provides electricity to the electrical system of a Cessna 172? Is the alternator connected to the electrical components directly and battery is only used in the event of an alternator failure? If the battery is only used as a backup solution, why does it require a continuous charge to it? Thanks


1 Answer 1


The alternator is the primary electric source on the 172. However, the main battery does supply the power to the rest of the system (Alternator supplies battery, battery supplies to the system). Neither are directly connected to the electrical systems, but they are connected to the various electric busses that then connect to the rest of the system. The batteries are not continuously charged but have a voltage regulator that senses if the voltage in the batteries gets too low and sends power from the alternator to the battery.

Page 7-48 from the PIM for the 172S NAV III GFC 700 AFCS has a good digram for how everything is connected. Page may vary depending on what model you have a PIM for. enter image description here

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    $\begingroup$ The voltage regulator on most Cessnas (including the 172) just adjusts the field voltage to provide a constant output, specifically 14 volts. Under all realistic conditions, the battery voltage will be less than 14 volts and so the batteries will not be supplying power because the regulator will be pushing the voltage higher than the battery can. $\endgroup$ Commented Jul 15, 2023 at 10:22

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