Ground system problems
As we noted in the April 2001 AMT "Radio Noise" sidebar, the ground system can present some of the most serious troubleshooting challenges. Many technicians change alternators, regulators, wiring and other charging system components only to find that the aircraft has a bad ground system. If you have more than 0.2 ohms resistance in the ground system from either of the alternators to battery ground, it is time to start cleaning connections. Recall that other "usual suspects" of a bad ground can be the field circuit breakers or alternator switches. To troubleshoot this, measure the voltage at the bus bar with the system turned on and the engines not running, then check the voltage going into the regulator. If any breaker or switch has more than a 1/2-volt difference from the input side to the output side, then it is probably defective, and should be replaced. To determine which one, you will have to go directly to the switches or circuit breakers.
Anomalies associated with temperature variations
Another consideration in setting up the alternators is temperature. Alternator current is inversely proportional to temperature; that is, output decreases as alternator temperature increases. You might have two alternators perfectly paralleled when cold, but after they warm up they become unacceptably out of balance. Have the pilot verify the balance on the first flight after an alternator is replaced or reinstalled; you may have to adjust the system when the plane returns.
Some regulator models are also more heat-sensitive than others. The installation location of the regulators might also increase (or decrease) this effect. Some regulators even require a heat sink to dissipate the heat that they generate, so (once again pointing out the obvious) be sure to read the manufacturers' instructions. If you don’t have sufficient information, don’t hesitate to call the manufacturer for technical assistance.
When aircraft charging systems go wrong, it can be tempting to look at the situation from the bad side and get frustrated. But bad perspectives can result in bad outcomes. Hopefully these articles on charging system troubleshooting have provided information that can help keep your perspective optimistic. Here's to your successful outcomes.
Mike McCluskey is a Technical Service Representative and Winston Greer is Vice President of Quality for Electrosystems, Inc. in Fort Deposit, AL.
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