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Old 28-05-2019, 19:11   #1
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Overcharging - Why?

I recently installed a new battery charger - Pronautic 1250 and went to the Bahamas for 6 weeks. I suspected that my two 4D house bank was sulfated so I did an equalization.

During the trip, they quickly ran down, so I charged often. The house bank also starts the stbd engine. There is another 4D for just starting the port engine and another 4D for the windlass and bow thruster.

Just before leaving to come back (14 hrs running), I noticed that the port non-house bank battery was very hot. I refilled it with distilled water.

On the run home, I smelled gassing. On getting back to my home slip, the smell was very bad and the three 4 Ds were hot. The port one was wet.

The battery charger was off for the 14 hr run. Why did the alternators overcharge when they never did before with the old (20 yr old) charger.

Did the new charger somehow kill the alternator diode packs?
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Old 28-05-2019, 19:24   #2
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Re: Overcharging - Why?

Depending on how they are interconnected, a bad cell could also be the cause of other problems such as you describe.
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Old 28-05-2019, 19:42   #3
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Re: Overcharging - Why?

We just had a very similar issue, we'd installed a new battery monitor, and shortly after the batteries started overcharging like mad.

Double check your alternator connections, in our case I believe the grounding wire was loose, so the alternator wasn't getting proper feedback. If you've made changes recently, it could be something simple like that.
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Old 29-05-2019, 21:15   #4
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Re: Overcharging - Why?

the alternator and charger have nothing to do with each other. sounds like a bad battery.

did they have water before and after you equalized them?
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Old 30-05-2019, 10:17   #5
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Re: Overcharging - Why?

Quote:
Originally Posted by smac999 View Post
the alternator and charger have nothing to do with each other. sounds like a bad battery.

did they have water before and after you equalized them?
Thanks all - got new batteries and the battery charger is doing great. I think the port starting battery had a loose black (-) connection that may have become fouled when the electrolyte boiled. Would that do it?

Yes, I kept up with adding distilled water. It was the 14 hr run that destroyed the port battery. Above, it was suggested that a bad ground could do it. I'm going to watch that from now on! I also plan to test the voltage at that alternator with the engine running up to speed.
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Old 30-05-2019, 14:34   #6
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Re: Overcharging - Why?

Gene-
It also pays to check the alternator sense lead. With multiple batteries you may have a "one wire" system where the sense lead is simply tied to the charging output and the alternator is always thinking the batteries are always at whatever voltage it is putting out. With a more effective "three wire" system the voltage sense lead (from the alternator or from the external regulator) goes to one battery, or is switched with the banks, to tell the alternator/regulator what the actual voltage is.
Either way, if that sense lead comes loose or is corroded, the alternator will try to put out higher power to compensate--which can cook batteries.
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