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2 Answers

C-172 Electrical system

Asked by: 5343 views Aircraft Systems

What keeps the electrical system from overcharging the battery?  I thought the voltage regulator provided this protection but during a recent discussion with an assigned CFI at my flight school, there was doubt raised.  What is the answer?

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2 Answers

  1. Wesley Beard on Dec 27, 2010

    It is the combination of the alternator and the regulator that keeps the battery from overcharging.  The alternator voltage is regulated by the voltage regulator.  The amperage is controlled by the output of the alternator and the regulated voltage.
    When the battery is charged it is said to have a certain amount of electromotive force (EMF).  This force pushes back against the electromotive force of the alternator current.  When the battery needs charging, the battery EMF cannot withstand the EMF of the alternator and thus the battery accepts the current and charges itself.  When the forces are equal, charging stops.
    With this method, it is impossible, without a failure of the alternator, to overcharge the battery.  It’s a pretty slick method.

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  2. Jim Foley on Dec 27, 2010

    In addition to Wesley’s post, As you know, the batteries in small aircraft are generally 12 or 24 volt systems.  The alternators are generally a few volts higher, such as 14 and 26.  The volatege needs to be higher to counter act the EMF mentioned above, but is not a large enough difference to couse damage, unless it malfunctions.  Due to the physical properties of the alternators, such malfunctions are virtually impossible.

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