Originally Posted by b_rodwell
I have a Lagoon 400
S2 with 2 x 40 HP Yanmar motors. My cruising buddy has a Fountaine Pajot Lipari
41 with 2 x (I think) 40 HP Volvo motors. When using the motors
to recharge the house batteries, he seems to do it a lot faster. This is probably partly because I have 600 AH of house storage
and he has around 400 Ah. However that does not seem to explain all the difference.
Is there any reason for this charging time difference? Is there anything I could do to make my recharging faster?
Reading comprehension 101, it's your alternator(s).
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.. 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:
and these, too: