The alternator I'm using on the Tailwind is internally regulated and provides no protection to the aircraft circuits if it fails. The risk is that the alternator output voltage increases and damages the avionics and even the battery. The way round this is a crowbar overvoltage protection circuit - sounds crude and it is. Basically the circuit monitors the voltage on the supply wires and if it exceeds 16.2V shorts them out through the onboard thyristor. This trips the alternator field/alternator relay circuit breaker which disconnects the alternator from the battery and shuts off power to the alternator field. Many automotive style alternators will continue to generate even after the field supply is removed hence the need for a relay on the output. This is an emergency device which hopefully will not be needed as disconnecting an alternator when it is generating can result in further damage to it
. A high power transient voltage suppressor will be wired across the alternator output to protect it if the crowbar operates.
The alternator I'm using on the Tailwind is internally regulated and provides no protection to the aircraft circuits if it fails. The risk is that the alternator output voltage increases and damages the avionics and even the battery. The way round this is a crowbar overvoltage protection circuit - sounds crude and it is. Basically the circuit monitors the voltage on the supply wires and if it exceeds 16.2V shorts them out through the onboard thyristor. This trips the alternator field/alternator relay circuit breaker which disconnects the alternator from the battery and shuts off power to the alternator field. Many automotive style alternators will continue to generate even after the field supply is removed hence the need for a relay on the output. This is an emergency device which hopefully will not be needed as disconnecting an alternator when it is generating can result in further damage to it
. A high power transient voltage suppressor will be wired across the alternator output to protect it if the crowbar operates.
