Larry wrote:
Snip

In figure 4-3 on pdf page 61, notice how the 3-stage charging is measured
in HOURS, not running the diesel for 30 minutes like boaters dream of.
Notice how the current drops very rapidly near the start of the charge,
not when the charge is near complete. My assertion of why it's stupid to
put a 140 amp alternator on a little sailboat diesel is obvious.

Snip

In fairness, typical automotive chargers are not rated for use with the
aggressive, constant-current charging cycles used in popular marine
"smart chargers". Replacing the stock alternator with a higher-rated
one when switching to a smart charger is not a bad idea, providing
engine, pulleys, and belts are also willing.

I agree that 30 minutes is not going to restore 50% of capacity on 200
Ah deep-cycle lead acid batteries. With a 140 amp alternator, gasses,
venting, etc., permitting, it would take more than an hour. Hard to
generalize, but with an adequate alternator, belt, engine speed and
charger, it is heat and gassing that ultimately limit the rate at which
you can jam amp-hours into a storage battery, and the better smart
chargers monitor terminal temperature and fold back current to try to
keep things intact. Haven't heard many horror stories of smart chargers
destroying batteries.

Remember too, even though you recover most of the lost charge quickly
through constant-current charging, that last 10-15% is what will take
hours to accomplish under typical voltage-limited charging, even with
smart chargers. So the author quoted is perhaps overconcise in his
statements.

Don't sell the smart chargers too short, Larry! ;-)

Chuck

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