Originally Posted by Espiritu Buho
Doing some routine maintenance
on my Tayana 48 CC, I noticed a slight crack in my Hitachi 12V-55A alternator. ...............................
Don't know if the Maine
Sail links include this.
Some alternators though, such as those made by Hitachi and found on Yanmar
diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?
Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage
based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking
itself. Remember voltage is the pressure that allows more current
to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. Any battery at any state of charge simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?
The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....
If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.
If you have a temp compensated alternator or a Hitachi alternator on a Yanmar
you really are in dire need of external regulation if deep cycling a larger battery bank.
This is from:
and these, too: