One difference between car and aircraft alternators is the presence of circuit breakers. I had repeated electrical failures, each one followed up by changing something (alternator, regulator, overvoltage detector, all the wiring) and still the failures happened. Until one day, failure in flight, I flicked, (not pushed) the field breaker. Bingo! the breaker operated normally until it decided to go open circuit and being of the push only variety could not be cycled. Of course after landing it worked perfectly. I even diverted over the Baltic because of this £0.20 piece of aviation rubbish and worse persuaded a colleague to hand carry an alternator to Helsinki! (interesting x-ray discussion).
GA CBs are a really crap implementation. They are thermal and since the heat dissipation in a resistor is I^2 * R, it’s obvious that the thing is going to run hot at any significant % of the rated trip current. Then you have to make the thing work over some plausible ambient temp range, bearing in mind that it will be mounted close to other CBs which also run, ahem, hot! It’s a stupid design. They also gradually wear out from the constant heat cycling and eventually they fail. The only salvation is in the form of modern aircraft usually drawing far less current than they might have drawn 30 years ago.
I had no end of alternator & regulator issues some time back on one of my C152’s, at the end of the day the resolution of the issues was to replace all the electrical cables forward of the firewall.
Thirty years of living in a hot engine bay being exposed to heat, engine oil, exhaust fumes and rain is not an enviroment that is conducive to reliable performance from electrical cables.
One issue I frequently see is that people start to exchange components without measurements. There are MANY single point failures which will result in low voltage. Relative inexpensive parts are often overlooked, such as switches, circuit breakers, over voltage protection.
GOOD measurements are very important. That means measuring voltages at different points when the system is ON / under load:
Also check all wiring and be sure to measure ground leads with a bonding tester. Do not replace parts before the above measurements are carried out. The testing above should not take to long and will give you a good indication of what is wrong.
