IMPORTANT - this only applies to standard deep cycle lead acid batteries (sealed or vented) other batt technologies need different charging
setups if they have higher charge acceptance rates. (such as lithium or NiCad and some 'high tech' lead acids like cyclone cells)
Absolutely not, would not even consider one on most boats. The alternator
output should be no more than 1/5 the battery
capacity and 1/10 is fine so 10-20a for each 100a/hrs in the bank. Anything bigger gives little advantage and will rarely be used. The alternator output is governed buy the charge acceptance of the batteries not the alternator output. The most efficient charge is at the 10hr rate which will get you to 90% at about 14.8v. Up that to the 5hr rate with a higher output alternator and you are only at 80% when you get to 14.8v. The charge rate then drops dramatically so the time gained on the bulk charge is lost
. There are time it can be worth it of course but not as often as you might think.
You can 'marinize' and alternator by opening it up a spraying with a high temp conformable coating and replacing steel
bits with stainless, this is what high end ones do. But a standard auto is designed to run under the hood
of a car with loads of salt
spray from the wheels, they are pretty tough and personally never had one fail through corrosion
is potentially an issue. It is said that standard auto alternators are not rated for the continuous high output you get from charging
. This is tue but in prctice not usually a problem, here is why. On a car the rev limit is between 6-10,000 rpm
so the alternator pulley is size for that speed, on a boat it is more likely 3-4,000. Most alternators don't develop full output until they are doing about 90% of there max speed so when you put a 100a alternator on a boat engine
it is going to give about 60a max unless you do some major work on the belt pulleys. Effectively you have just de-rated it to an output it can continuously maintain without overheating!
So unless you run a batt bank above 750a/hr a standard 85-120a auto alternator is fine. Save the money
and install a decent 3step regulator
instead, will give you far more effective charging. I like the Sterling power ones but there are others.