outboards charging agm batteries

aweigh again

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Joined
Sep 8, 2011
Posts
290
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Location
meriden,ct
Boat Make
22 foot 1983 bass boat
I am thinking it might be exactly what you just mentioned, battery size. The amperage from the engine might be enough to pump those volts up too high on smaller batteries. I am no physicist or engineer, but my observations of marine DC systems are that getting your volt meter out and actually checking the performance of anything what you install in the system is very important. The reason I have the 31’s is I use an electradyne hauler heavily seasonally to haul dredges for scallops. That is a idle speed - 1400 rpm game mostly so charging is minimal but I always see 14.2 volts while fishing that way. Coincidentally, I was charging the batteries to continue my season prep yesterday and I noticed the 10 amp setting on my cheap 17 year old black and decker battery charger was pumping the batteries with 15.2 volts!!! So, I switched to 2 amp setting and it came down. I sometimes have had to bump to 10 amp for a short time to get the ACR to close (reach 13.8 volts plus on start battery) and allow current to flow to my house battery, charging it simultaneously. I use 2 amp charge when using this charger the few to four times each year I use it to maintain the banks.
Once I get the voltage situation under control I might install a battery monitor gauge to see what my typical usage is, and then decide what I need to supplement the alternator .
 
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