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Proper Output for Alternator

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Hey everyone,

I was out last week barefooting and went to start the boat and it was dead. We ended up having to drift to shore and get help for some city workers. Anyway my battery was a couple years old but I thought I would charge it good before heading on on Labor day with the family. I did and everything was fine in the morning when we were footing but i noticed the cranking was getting weaker. We left the boat running and ran some checks on it, we got 14.4 volts off of the alternator and about the same on the battery. We ran it to the dock and shut it off and it was dead as I thought it might be. We threw it on the trailer and ran to Wally world and got a new battery and continued our day. We didn't have any further trouble, but is seem to be cranking slower toward the end of the day.

Do you think I have other issues?

What is the proper output for an alternator?

Any other ideas?


Brad ;)

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That is the proper voltage output for an alternator. It also is putting out

"amps". It would be interesting to see the amp output. You would need

a tester like a shop would use for that. Lets say your alternator puts out

60 amps max & you were running a stereo with amps & the heater,etc. and

it was using 80 amps. Your alternator could be putting out the 14.4 volts,

but your battery would still be slowly going dead.

If you were not using any electrical equipment out of ordinary on this day,

that would not be the case. Your battery could have went bad - sometimes a plate

inside of it will shake loose & "short out" inside the battery. The only

thing unexplained is if the new battery is actually discharged at the end of

the day. Hopefully you were just listening "too hard" because of the problem

earlier in the day.

It is possible to have an alternator putting out good voltage - but not amperage,

if one of the "diodes" fail. The alternator has a diode trio & if one of the three

fail, you lose 1/3 of the charging amps, 2 & you lose 2/3, etc.

Testing the alternator would be best - either take the alternator off & to a

good parts store that can test alternators, or take a "shop style" alternator tester to the boat.

Edited by Hman442
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