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Bypassing the overvoltage protection --
What can you break if you do, in fact, have an overvoltage condition?
1) Certainly the radios. Don't turn the radios on and you'll be fine.
2) Maybe the electronic ignition system, if you have one. Tough to run the engine without it. However, if you have a magneto on one side, just run the engine with the magneto only and you shouldn't have a problem. Yes, it may run a little rough, but that shouldn't affect your overvoltage system investigation.
3) Relays and contactors -- I doubt you can hurt them with a short burst of 20-30V.
4) Engine monitoring system. Yes, you could fry this. But if the engine runs okay (good oil pressure, mostly) then I think you'd be safe in disabling it for your test. Probably need to pull a breaker or a power wire to make that happen.
5) Clock. Maybe you can fry this. Unplug it.
6) Light bulbs. Leave them off.
7) You probably have a controller for dimming instrument lights. It may be possible to fry that. Best if you disconnect the power to it for your test.
Beyond that, just don't turn things on and they won't get hurt. You probably will need to use a handheld voltmeter and maybe a handheld ammeter. I don't know what you're trying to measure. If you want to know if your alternator is putting out power, the voltage reading will tell you that all by itself. If your bus voltage is 12V or less, you're alternator isn't putting out (or the voltage regulator is busted). If the bus voltage is between 13 and 14 volts, then your alternator is working.
Of course, if your bus voltage is 18 V, then your voltage regulator isn't working but your alternator is -- I think. I don't know if there are alternator failure modes that have a high voltage output if the voltage regulator is working. I doubt that the alternator could fail that way.
I know a bunch of very good aircraft electrical engineers. If you give me some details, I'll talk to them and we can help you put together a troubleshooting plan. (Yes, for free...but you have to do the work!)
- Rob Wolf
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