Showing 11.6v while running... bad alternator or something else?

[gregtay]

Hi all, over the winter I had my dealer upgrade alternator on my M6 with the Malibu kit.  Sounds like they tested it and the boat was showing 14.2v when they were done (but I wasn't there, didn't see the result.)  Put the boat away for the winter.  Today I pulled the boat out and started it up on the hose.  When the boat was off I was seeing 12.1v (ish) on the dash.  Started the motor and the voltage dropped to 11.6v. I let the boat run, rev'ed it a few times... 11.6v.  hmmmm.  After 15mins I turned the motor off and the voltage jumped back up to 12v.  So.... the obvious answer seems to be "the new alternator wasn't installed correctly or it is not the correct alternator."  Before I drag the boat back down to the shop I figured I would check i with TMC if there is anything obvious I should be checking.  Batteries are only 2 years old (boat is only 2 years old and I have had the battery tender plugged in periodically throughout the winter (But not the entire 8 months.)  Just looking for anything obvious I should check.   I will note that when I picked up the boat the tech said the wiring for the new alt was a PIA.  I thought the Malibu upgrade kit was a pretty easy plug and play swap, so it has me wondering if Malibu didn't send the right Alt kit.

[Bozboat]

You said obvious, so are the battery cables tight at all ends?

[calilsv]

Sounds like a bad alternator if the wires are hooked up correctly.  It's being pulled down to 11.x because the electronics are putting a load on the battery and the alternator is not charging, and pops back up to 12.x once the load is stopped.

Biggest things to check would be the ground to battery's, but I doubt that's it since that shouldn't have been touched, and positive lugs in the engine compartment if they are located there.  Not sure how the 19 is wired, but it 17 they came from alternator to positive junction lug in engine compartment and then to batteries.

 

 

[gregtay]

14 hours ago, Bozboat said:

You said obvious, so are the battery cables tight at all ends?

I went out and pulled the battery connections off the battery side and reconnected them... just to make sure.  I will try the other ends today.

[gregtay]

14 hours ago, calilsv said:

Sounds like a bad alternator if the wires are hooked up correctly.  It's being pulled down to 11.x because the electronics are putting a load on the battery and the alternator is not charging, and pops back up to 12.x once the load is stopped.

Biggest things to check would be the ground to battery's, but I doubt that's it since that shouldn't have been touched, and positive lugs in the engine compartment if they are located there.  Not sure how the 19 is wired, but it 17 they came from alternator to positive junction lug in engine compartment and then to batteries.

 

 

There is a positive junction lug just in front of the motor on the port side.  The ground is also in that area.  I will go out today and check all the connections.

And yes "if the alternator is wired correctly"  From what I can see there are three wires on the positive post and one ground wire on the ground.  working to trace the wires (which is difficult since they are tucked between the exhaust riser and the motor.