Alternator problem???

[txarmydude]

I just bought a new deep cycle battery and charger. I slow charged the battery to 13.1 Volts and hooked it up in my 1977 Cobalt (5.7L 260 Mercruiser I/O). Starting the boat was not an issue. She started right up and ran just fine for a good 15 minutes. I kept checking and re-checking the voltage on the battery terminals with my voltmeter and it read either 12.5V or 12.6V every time. I even had the motor up at 4000 RPMs and the voltage was still the same.

Now, if I am working on a car and I see that the voltage when it is running is below 14.4V, I will be looking for a new alternator. Is the same thing true on an I/O boat?

 

[Bt Doctur]

Re: Alternator problem???

there is also wiring and maybe a "lawer fuse" in the circuit for the output to get back to the battery.Check Alt. output directly at the orange wire, if its a 3 wire check both small leads for power. Head up to the Adults Only section for your manual. it has all the wiring diagrams you need.

 

[NHGuy]

Re: Alternator problem???

And yes, it should run around 13.8 volts while running. The voltage you reported was battery voltage.

 

[txarmydude]

Re: Alternator problem???

What about old battery terminals? Could these be the culprit?

 

[NHGuy]

Re: Alternator problem???

Not likely, new fully charged lead acid batteries rest at 12.7 volts. Diagnose the non functional charge system/alternator. BT Doctor is very knowledgeable.

 

[txarmydude]

Re: Alternator problem???

Ok, I checked the voltage coming off the alternator. I used the screw that holds on the orange wire so I couldn't get any closer to the alternator and the neg battery terminal as a ground. Result: 12.4 Volts, no increase in voltage @ higher RPMs either. So, bad alternator???

 

[BajabossJD]

Re: Alternator problem???

Sounds like a bad alternator. Possibly voltage regulator ( which is in the Alternator)

 

[txarmydude]

Re: Alternator problem???

I kinda figured.... That sucks, these things are like 200 bucks new.

Has anybody ever had one of these things re-built? If so, where should I go to get one rebuilt?

Is it really that hard to do it yourself???

Last question, can you buy a Chevy 350 alternator, take the guts out, and use the old sealed marine case???

 

[Bt Doctur]

Re: Alternator problem???

http://www.iboats.com/Mercruiser-Al...6810911--**********.628668557--view_id.269735
If yours is GM you can go that route, but a good shop can rebuild it for a lot less.
new brushes are around 3 bucks,Unless its been wet, overloaded from a dead battery, or had the battery cables reversed, its rebuildable.

 

[txarmydude]

Re: Alternator problem???

Thanks for everyone's help! I'm going to take it off tomorrow and bring it down to the auto parts store. I might be able to get one of the employees to do it cheap!

 

[BajabossJD]

Re: Alternator problem???

I'll let you know. I'm about to open mine up in an hour. My voltage regulator is shot.. Over charging the battery.. I have heard you can buy the entire rebuild kit for $30 and reman it yourself... ??

 

[txarmydude]

Re: Alternator problem???

OK, so I removed the old alternator, looked at it and decided that it was not really a marine alternator to begin with. So like a dummy, I went and bought one for a 5.7L chevy. Anyway, I hooked it up, it worked fine, and when I went to shut the key off, THE BOAT KEPT RUNNING!!! I couldn't get it to turn off!!! I finally pulled the purple wire off the alternator and it shut off. But not without first getting a hand-full of voltage straight from the coil... OUCH!!! Sooooooooo...

Now what??? Is the problem with the boat not shutting off a result of the incorrect alternator, or what???

 

[txarmydude]

Re: Alternator problem???

I got the old alternator back this morning, so back to the drawing board!

 

[txarmydude]

Re: Alternator problem???

I replaced the alternator with a brand new Mando marine alternator. Everything works just fine now, and the battery is charging perfectly! Thanks to all you experienced boaters for the advice and ideas. I'm sorta figuring this stuff out as I go along!