The alternator is self regulating. On a smaller boat with a setup like this I usually recommend a cigarette lighter plug
. You can get these at auto parts
stores, target, walmart etc.
The voltage while motoring should read around 13.5-14v and with motor
off around 12.5v.
What is bad for the batteries include high charge rates - >14v or so, draining them to dead and sometimes mixing of battery
What will kill your alternator is shutting of the battery
switch while motoring. This is something new boaters sometimes don't understand.
The regulator receives a sense or feedback, from the system voltage. If the voltage is below the regulated voltage (~14v) the alternator cranks up the output. If the battery switch is turned off the alternator sense zero and goes into an over-output mode which can and will fry the alternator.
The other reason the alternator can go in overvoltage mode is if the sense line breaks or is corroded. Monitoring a voltmeter as mentioned above can alert you to something going wrong. Periodic inspection
(annually?) of the sense line and cleaning
the connection is also good preventive maintenance
During haul out
every year I remove and clean all the battery terminals, I disassemble and clean all the connections on the main switch and I remove and clean the connections on the alternator. The sea is a harsh environment