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mfshook62

Well Known Member
Alternator Warning Light - Under and Over Voltage Protection

I built and installed a solid state alternator warning light system that runs off the +12v buss and is driven by a couple of op-amps. My new 60 amp auto? alternator from Vans does not have an output that will alert the pilot to an under or over voltage condition. An over voltage condition could cook the battery and possibly burn out some expensive electronics. I built this circuit, because I don't have an engine monitor or any other type of charging system alarm. The only evidence that there is a charging problem is if I happen to notice a low or high dc voltage on the voltmeter. So, I built a circuit that would warn me if there was a problem with the alternator charging system. The circuit is activated by the master switch and drives a single bright red LED mounted on the panel to indicate a voltage less than 12.40v or greater than 14.70vdc. It could also trigger an audible alarm. I bench tested the circuit using a power supply, and then installed it in my RV9a. It warns me if the alternator is not charging or if it is overcharging the battery. It has been installed for the last 6 years, and Im very satisfied with its performance. Let me know if you have an interest in this circuit.

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I have a warning light

I would have to go back into my schematic to verify it but as I recall it is driven by the B&C voltage regulator. It is very helpful and enabled me to avoid a trip ending landing and preserve the battery for use at the final destination on one trip. It is a good idea.

Bob Axsom
 
Most engine monitors can be programmed for alarms on overvoltage, undervoltage and undercurrent. This might be enough to detect a faulty alternator.

Vern
 
I think that the fewer the lights the better. A Red one for the alternator not working is a good idea. I have one which is driven from the alternator controller, but I'd drop the other lights. Too many lights that are on all the time (like Green) just get ignored eventually. Just my $ .02.
 
When the alternator and voltage regulator are working properly, the field wire is powered, and the engine is running the bus will be at about 14.2 volts. When the alternator/VR fails, the bus will drop to the battery voltage which is about 12.4 volts, and decay from there depending on the load.

So all you need is circuit that turns on a light when the voltage is below about 13.0 volts. The Vertical Power system and many EFISs have alarms for this condition. You can also buy a stand-alone low-voltage alarm module from B&C and others.
 
Dark cockpit theory

f1rocket said:
I think that the fewer the lights the better. A Red one for the alternator not working is a good idea. I have one which is driven from the alternator controller, but I'd drop the other lights. Too many lights that are on all the time (like Green) just get ignored eventually. Just my $ .02.
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Most modern airliners are designed using the "dark" theory, that is, when everything is normal there are no lights or warnings showing. Randy is correct, anything that is on all the time becomes invisible after a while.

John Clark
RV8 N18U "Sunshine"
KSBA
 
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