Is my alternator going bad?

[paul40269]

I have a 2008 Optimax motor with 70 hours on it.

Took boat out yesterday, hadn't charged batteries in two weeks and forgot to juice up before my trip. (dumb, I know, but I have lithium trollers and a lead acid on the same charger and had it unhooked due to cold weather).


Boat started fine in the morning, ran 5 miles to a spot. Fished an hour, boat started ok again, then halfway to another spot, about 4 miles away, voltage on dash meter was dropping. It was reading 10volts on the dash and an alarm was going off. This happened to me last summer but at that time the battery was old and tested bad.


Got home, tested battery. Wingnuts on battery were a little loose and battery tested around 12.06 volts.

I then put battery on charger, fully charged and then tested the battery and alternator.



Results:

Fully charged battery read 13.23 volts

Multimeter on the alternator with boat idling in the driveway, and in gear is between 12.42-12.94v.

I did not rev up the RPMS high.

I'm pretty sure I need a new alternator. If so, should I have it rebuilt or buy a new one? 2008 Optimax.

[JOE54]

fuse link tested ??? all fuses checked on engine ???? need to replace wing nuts with stainless nuts and lock washers

[paul40269]

fuse link tested ??? all fuses checked on engine ???? need to replace wing nuts with stainless nuts and lock washers

Fuses not checked yet.

[EuropeanAM]

Also WHICH Optimax motor do you have (preferably with serial number)?

[paul40269]

Also WHICH Optimax motor do you have (preferably with serial number)?

2008 Optimax
Model: 1090D73HY
Serial # 1B533084

Latest test ran today:

Battery with boat idling: 12.34v
Alternator voltage idling 10.83v

In gear with some throttle, around 1500-1800rpm (on muffs in driveway)

Battery voltage 12.75
Alternator 10.34v

Small plug going into alternator

Key off:
Purple wire: .06
Red wire 11.37

Key ON
Red wire 11.32
Purple 10.91

I tried testing the 100 amp fuse coming out of alternator for continuity but multimeter will not take a reading through the plastic sheathing.

Thank you.

[JOE54]

very low batt voltages

[paul40269]

very low batt voltages

The battery was bought last August, not that that means anything. I will probably buy a new battery to test it again to see if anything changes before committing to changing alternator, but the alternator should be creating a reading of 14v according the service manual I found online last night. I'm not even close here.

Hopefully European AM can add some more insight!

[paul40269]

Update. Brought alternator to rebuild shop. They verified it was bad. Having it rebuilt.