For many pilots and mechanics, troubleshooting an alternator system is typically done by using the shotgun method. For example, if a new battery doesn’t fix the problem, let’s try a new regulator! Still not fixed? How about a new alternator? Nope, still not working? Well let’s replace every other part until the problem is fixed. Well, with the way the world works, nine times out of ten, it’s the last part replaced that will fix the issue.
If you understand how easy and simple the design of an alternator is, troubleshooting can be a piece of cake for anyone that has limited electrical knowledge. If you don’t have to replace parts that actually work, then it’s easier, faster, and cheaper to get back where every pilot really wants to be, in the air.
What is an Alternator?
Like I said, if you understand the design of the alternator and what it does, troubleshooting is much easier. So, what exactly is the alternator?
Alternators are a widely used invention that can output alternating current (AC) at levels of 100 volts or more. When used in a 12-volt charging system, the alternator output is converted to direct current (DC) using diodes.
The basic function of your battery is to start the engine. Once this occurs, your alternator has the job of continuously supplying electrical power to all of the equipment on the aircraft and recharging the battery as well.
Although alternators are a great, powerful invention, they are quite sensitive. Alternators are able to produce full rated output at low engine RPM. This means that GA aircraft are full of avionics which require more power from the very beginning of each flight. Light aircraft alternator systems weren’t always so dependable.
A crucial piece of your aircraft is the voltage regulator. The voltage regulator varies the strength of the magnetic field generated in alternators and generators. A generator produces electrical power when the aircraft battery is completely discharged, as opposed to the alternator which cannot produce power when the battery is completely discharged due to the lack of permanent magnets.
Learn about Load Shedding
Without a backup charging system, you need to understand load shedding. AOPA gives a good example on their website:
“A fully charged battery is a bank with limited assets. Each electrical circuit is a drain on those assets. The point of load shedding is to turn off all unnecessary drains (circuits) in order to preserve, and best use, the battery’s limited assets.”
If you lose your communication and navigation capabilities your issues can begin to snowball quickly. Load shedding will, if properly performed, increase the time until this could possibly happen.
By locating the switches and turning off items requiring power that are not essential for flying you can alleviate some power issues. For example, no one is going to fault your decision of turning off the position lights in an emergency situation.
Always be sure to know your circuit breakers as well as your aircraft service manual before attempting any load shedding.
Alternator On/Off Switch
A little corrosion or wear in the inexpensive alternator on/off switch can lead to some major problems.
Often overlooked, this switch could be another cause of your alternator system issues. Make sure this switch is resistance-free, and it isn’t throwing off the system voltage sensing function of the voltage regulator or AC.
Alternator Ripple Tester
A great tool for troubleshooting rectifier problems is an alternator ripple tester.
If your engine electronics seem to be performing erratically, one or more marginal diodes in the alternator may be leaking. These diodes will generate alternating current ripples along your electrical system.
Test by taking a digital meter and setting it to AC mode. Then select a voltage range to read approximately 2 volts, and start your engine. You should have less than 0.1 volt AC, the lower the better. You could also use an oscilloscope.
If All Else Fails
It may sound funny, but reading the directions can actually help quite a bit. Manufacturers frequently include installation instructions, but occasionally this information gets removed.
If you read the manufacturer’s bench test report and see that the unit came off their production line operating properly, then it is most likely something other than the unit.
Of course, this is the real world and nothing is ideal, so things are not always kept simple or compatible. Piper’s systems can be different from Cessna’s. Some of the newer alternators have the voltage regulator inside of it, and many aircraft have 24-volt systems as well. All of these components can cause it to be more difficult or confusing for the mechanics that work with all the different manufacturers and models of aircraft.
All of the systems can’t be discussed in detail, but these are just the basics. Once a charging system is understood, it becomes a lot easier to understand how your specific design really works. If things go wrong with your charging system, avoid the shotgun method by knowing your system.
Alternators are one of the best inventions for electrical systems in history, but they can be touchy at times. If you have any further questions about your charging system or parts, please contact our very knowledgeable sales team at 800.362.3044.
Do you have any other tips you have come across when dealing with your electrical systems? Comment below and let us know.
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