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As the Wrench Turns

AS THE WRENCH TURNS

David Vital, Director of Maintenance davidvital@wvfc.org


AIRCRAFT CHARGING SYSTEMS

 

Happy Autumn West Valley Flying Club!! I hope everybody had a wonderful summer and made all of their flying hopes, dreams, and desires come true. This month we will give a basic description of how the aircraft charging system works. Troubleshooting an alternator-system problem usually involves the shotgun approach. If a new battery doesn't cure the ailment, perhaps a new regulator, alternator or other component will. Murphy's Law always prevailing, nine times out of ten, success arrives only after the last component in the system has been replaced.

By understanding the simplicity of the alternator design, troubleshooting can be a cakewalk for anyone who can at least figure out how to replace a burned-out light bulb. The modern alternator used on aircraft charging systems today ranks as one of the most important inventions in all of technological history. Few devices have been produced and used in greater number than the alternator.  It is a marvelous little standalone dynamo that can output alternating current (AC) at levels to 100 volts and more. When used in a 24-volt charging system, for example, the alternator output is rectified (converted) to direct current (DC) using diodes, then clamped at approximately 28.4 volts with the aid of a voltage regulator.

Engine starting is the basic function of the battery, after which the alternator supplies continuous electrical power not only to all essential equipment on the airplane, but to recharge the battery as well.

The regulated voltage (28.4) to the system bus is somewhat higher than the battery voltage (24 volts) so that alternator current flows to the battery to charge it. If the regulated output were, say, only 23 volts, battery current would flow to the bus instead, eventually discharging it. So to keep a full charge, the regulator must clamp at something greater than 24 volts, but not so high as to boil the battery or damage onboard electrical equipment. Thus, 28.4 volts (+/- .4 volts) is the industry standard for charging systems using 24-volt batteries.

As we move into fall and the winter months the maintenance department would like to remind you that the spring-summer end of month BBQ’s will be turning into autumn-winter MX Q&A pizza parties starting in the month of November!! We will have a couple of airplanes in the hanger opened up for viewing and questions for you the members. The first MX Q&A Pizza Party will be held on Friday November 22, at 12:00 p.m. So save the date and come join the fun, we hope to see you there!!

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