Battery over charging

Don O'Gorman

Member
May 28, 2020
46
Boat Info
1985 Sea Ray Seville w/ a 1992 Mercruiser 140 3.0 engine. Alpha 1
Engines
Mercruiser 140 3.0 Alpha One out drive
Hi, Brand new to here so I hope I am doing all this correctly. I have a 1985 Sea Ray Cuddy Cabin with a 1990 Mercruiser 3.0 Alpha 1.
I am noticing that my voltage at my fishfinder while running is between 15.4 and 15.6 volts. I know that is over charging but the battery doesn't feel hot nor is it swelling. So my question is: Is the alternator charging at a dangerously high voltage?
Thanks Don
 
What does your dash volt meter read? I would get a good digital multi meter and verify battery voltage at full charge and charging voltage first to see whats really going on. How old is the battery and when when was it last serviced?

If its charging at 15.x V its too high and could be a bad voltage regulator. It could also be several other things. Get those voltages and report back, that will help diagnose.
 
What does your dash volt meter read? I would get a good digital multi meter and verify battery voltage at full charge and charging voltage first to see whats really going on. How old is the battery and when when was it last serviced?

If its charging at 15.x V its too high and could be a bad voltage regulator. It could also be several other things. Get those voltages and report back, that will help diagnose.

Thanks for replying. I should have told you all that. Volt meter at dash is unreliable...original I think. Battery is brand new. Multi meter reads 12.9 - 13.1 with nothing attached. While running the reading matches what the fishfinder say which is about 15.5. My theory was the regulator also but was hoping to not have to get a new alternator if you felt that the charge wasn't at a dangerous level. Just an after thought....could my belt be on too tight and if so how do I know what the correct tension should be?
 
Definitely not the belt. That sounds like a bad voltage regulator, so a new/rebuilt alternator is needed. I would NOT run the boat until you get that fixed, or you will kill the battery as well.

Not a bad job and a local autoparts store can test to confirm on a bench. Another thread had some places to get marine rated alternator for a good price. DBelectric.com,

What kind of battery? If standard lead acid, make sure you check the electrolyte level and replentish if necessary. That high of a voltage can cause gassing and a drop in the cell levels. Replace with distiller water.
 
So it's a Sears die hard deep cycle battery. It looks like it's a maintenance free battery but will double check to see if the cells can be accessed.
Thanks for the link and I'll have to spring for a new alternator.
Since this an older boat I will probably be posting a lot more questions
Thanks again
 

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