Proa

Hitachi 55 amp alternator

So where does the voltage sense wire from the alternator connect to the system. After 10 years, there is probably some corrosion on the connections and terminals which could effect the voltage both at the sense connection and on the high amp wiring.

Also, what was the SOC of the batteries. Alternator output is based on SOC of the batteries. If the batteries were mostly charged then I would expect about 35 amps out of the alternator. The Amp output of the alternator is not constant and is reduced as SOC and internal battery resistance rises. The alternator will only put out what the batteries and system will accept.

In the 80's and 90's, the thought was to install a 100 amp or larger alternator. Mainly to reduce engine run times while charging at anchor. Now a days with solar and wind being the primary means of charging, I really don't see why people are still spending big money on high output alternators.

Really its a bit outdated to put a 100-200 amp alternator on a boat when at anchor the power is coming from solar and wind (or a honda generator). I find that when I motor its for hours at a time, so the 55 amp hatachi works very well without excess side loading on the water pump bearings or larger belts.