Nope, alternators get hot. But...
Hitachi/Yanmar Alternators: (by
Maine Sail)
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 absorbtion voltage, then we also reduce the
current the alternator is supplying.. The
battery 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:
Musings Regarding External Regulation - SailboatOwners.com
and this, too:
http://www.cruisersforum.com/forums/...on-125843.html