Taking Charge of Alternator Problems Part II
Multi-engine alternator charging system troubleshooting
By Winston Greer and Mike McCluskey
Multi-engine electrical systems are nothing more than single-engine systems coupled together to make them work as a unit. Continuing the treatment of alternator troubleshooting from our initial article on this subject in the April 2001 issue of AMT, for this installment we will be discussing twin-engine applications.
If you are an optimist, then you might consider twins an "opportunity" for:
1. Performance improvement
2. Increased safety through engine redundancy
3. Revenue-enhancement of your operation
If you are a pessimist, then you might think of twins as just a way of doubling your "problems." Somewhere between these two extremes lies reality. With more knowledge about troubleshooting twin-engine charging systems, you are more likely to adopt a more optimistic perspective.
Let’s review the basics. An alternator is an electro-mechanical device that converts mechanical energy to electrical energy. A regulator is an electronic device that controls both the voltage and the field current of an alternator. Fundamentally, all of this sounds quite simple — and it is, but interesting outcomes can occur if everything is not "just right." Many of the topics covered in this article are expansions on the fundamentals discussed in the April 2001 installment, Taking Charge of Alternator Problems. The fundamentals of troubleshooting single-engine charging systems are the same as those for troubleshooting multi-engine applications. However, significant differences do exist between single and multi-engine applications. This expanded
treatment of the subject should help to resolve some of the more perplexing problems associated with multi-engine alternator systems.
High Frequency Regulators
Recently, the major reason for changing regulator equipment is to upgrade to newer designs that operate at a higher frequency than earlier designs. Higher frequency (faster) regulators tend to eliminate the "wagging needle" on ammeters that earlier-designed regulators were prone to cause. These older regulators generally operate at a frequency close to the alternator frequency. As a result, the regulator tries to "follow" the alternator and vice versa, causing the pulsing or wagging of the ammeter indicator. Another major reason for changing to newer-design regulator equipment is the advantage of built-in ground-fault protection. From a cost-to-benefit ratio standpoint, this is one of the great newer developments in regulator design. With earlier-designed regulators, a short in the alternator field would "blow" the regulator. With ground-fault protected regulators, the regulator is not damaged, and an LED comes on to alert of the ground-fault condition. This is also a great diagnostic tool. If an alternator keeps dropping off-line and the LED comes on, then you know the failure mode is the field circuit. This feature saves a lot of time (and money) when a ground-fault problem occurs. Some technicians keep this type of regulator in their toolbox and utilize it as a diagnostic instrument when the airplane they are working on doesn’t have the newer-design type of regulator. Paralleling ramins the most challenging aspects of installing alternators or regulators i twin-engine applications.
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