# 5.7 alternator not charging battery



## Rockstar (Jun 4, 2010)

Replaced the alternator, still isn't charging batteries. Thinking maybe the voltage regulator? Anyone have a similar problem?


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## DontForgetTheDrainPlug (Mar 3, 2010)

Could be wrong but I thought voltage regulators have been integral in the alternators for many years.

What year is your motor?

Otherwise, obvious answer is bad batteries, but maybe you had them checked???


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## Rockstar (Jun 4, 2010)

its a 1989 merc and they brand new batteries


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## little d (Dec 10, 2008)

I would start by taken alt off and take it to a good place to have it checked! also did you replace it with a marine alternater? autozone,advanced can check em but dont thing they sell them.


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## Misdirection (Jul 16, 2012)

Buy a volt meter and start tracing from your alternator to your battery. I suspect your voltage regulator is bad, bit a volt meter is cheap ($20) and has many uses...

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## Rockstar (Jun 4, 2010)

we were suspecting the voltage regulator but I'm not sure where it would be located in the boat.


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## hearttxp (Dec 21, 2004)

No such thing as a regulator on that motor ! Either have Bad connections some where or got another Bad alt ? Have it checked out by a place that can check it. Just don't quess. replacing it isn't always the fix. Might even be a dead cell in a battery ?


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## Misdirection (Jul 16, 2012)

As stated above, yours may be internal to your alternator, so pulling it and having it tested may be a good option.

With a volt meter you can check your wiring. You should read 12.6 volts with your engine off. If you disconnect the purple wire from your alternator (the excitation wire) and check the orange wire output you should still show 12.6. If you get 0, that indicates a problem in a wire, possibly a break somewhere along the line.

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## Rockstar (Jun 4, 2010)

ok thanks for the info will get checking some more thanks


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## DontForgetTheDrainPlug (Mar 3, 2010)

According to info I found... IT DOES have a voltage regulator and IT IS built in to the alternator.(internal). At least on car engines. Been that way since 1980's.

Take the alt. out, or take the boat to AutoZone etc.and have it tested.


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## hearttxp (Dec 21, 2004)

Thus saying if you replace alt with new or rebuilt it will also have a new or checked out regulator ? 

Yes what did you replace alt with ? New -Used - or rebuilt ? and YES by all means make sure it is a MARINE ONE !


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## Workdog (Jan 10, 2007)

I don't know that motor, but a couple questions first, then a couple more things to check... How did you determine the batteries weren't charging? By a dashboard gauge, or with a multimeter at the battery posts while the motor was running? Measure volts at the battery with the motor off. Like Misdirection says, a fully charged battery should read 12.6 volts or so. Then, when you start the motor, does the volts increase (14.3-14.6 or so would indicate the battery is charging...sometimes at idle power setting you may only be getting 13.5 or so). 

Have the alternator and battery(s) been load tested good (they will check this for you at Advance or Auto Zone for free)? With a multimeter set to resistance (ohms) setting is there continuity between the case of the alternator and the block? Your alternator may be getting its ground by metal to metal contact between the case of the alt and the mounting point. If there is no continuity you would need to clean the contact surfaces. With the multimeter in the resistance setting, check the positive wires at the alternator and the other end attach points/battery. Here you would be checking for a break in the lines. By the way, is there a fuse that controls the charging circuit? Finally, there is a connector on the motor that connects the wiring harness to the motor. If you pull that apart, you should see a lot of pins an inch or so long on one connector. Each pin will be round and split down the middle. You could widen the gap on each pin so there would be good contact with its mating female side. I had a problem there once on an earlier model 5.0L motor (when I tilted the lower unit it would cause the engine to misfire...widened those pins and problem went away).


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## Rockstar (Jun 4, 2010)

Just tried autozone and advance auto neither one could test it for some reason but found a guy in the area that can but isn't home till after 5. its a used marine alternator and the guy said it was good, but will know more after testing it. Workdog I had the boat out and had to have a buddy bring me a battery to get started after it running for a half hour or so and it started fine at the dock with no hesitation, so brought the boat home charged the batteries took it out again this time only ran one battery after fishing for awhile tried to start the motor had to switch to the other battery to get it running again the dash was saying 12 volts and turned the low voltage alarm on the fish finder and it would go off at 11.5.


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## DontForgetTheDrainPlug (Mar 3, 2010)

hearttxp said:


> Thus saying if you replace alt with new or rebuilt it will also have a new or checked out regulator ?
> 
> .....Good question...but whether its new, rebuilt, or untouched, there's a voltage regulator inside. If there isn't, that would explain the problem


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## Workdog (Jan 10, 2007)

Rockstar said:


> *Just tried autozone and advance auto neither one could test it for some reason *but found a guy in the area that can but isn't home till after 5. its a used marine alternator and the guy said it was good, but will know more after testing it. Workdog I had the boat out and had to have a buddy bring me a battery to get started after it running for a half hour or so and it started fine at the dock with no hesitation, so brought the boat home charged the batteries took it out again this time only ran one battery after fishing for awhile tried to start the motor had to switch to the other battery to get it running again the dash was saying 12 volts and turned the low voltage alarm on the fish finder and it would go off at 11.5.


Makes sense. Advance or Auto Zone could load check the batteries, but the engine would probably need to be running for them to check the alternator. 

From your last sentence it sounds like you might have one hell of a drain on the battery there, to die in a half hour. Let's see what the alternator checks out as then go from there. You should still run thru the other items I mentioned.


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## Rockstar (Jun 4, 2010)

Got it checked and its junk gonna check the other things out and just buy a new alternator


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## bountyhunter (Apr 28, 2004)

alternators can be rebuilt to like new condition, for half the price of a new one.


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## KaGee (Sep 8, 2006)

bountyhunter said:


> alternators can be rebuilt to like new condition, for half the price of a new one.


If you can find a shop qualified to rebuild a marine alternator.


If one plans on doing his own service, a factory shop manual is a very wise investment.


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## sherman51 (Apr 12, 2011)

you can get all kinds of mercruiser alternators off ebay for less than 75 bucks. they even have a chrome one for like 95.00. or you can get an arco oem for around 175.00 or overtons has the mando,s for about the same price.
sherman


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