Alternator Issue??

[Kimber]

Had the boat on Lake LBJ all week, and noticed right away something wasn't right. After launching, I noticed that the volt gauge was only reading 11. Ran the boat all day, then battery 1 died and would not start the boat - switched to batt 2 and started no problem. Charged batt 1 all night, and it was dead by lunch the next day. It was 4 years old, so I figured this might be part of the problem. Bought a new Interstate and installed as batt1. Boat ran well that next day until late afternoon, then had to switch to batt 2.

Tested the batt after full charge woth volt meter - 12.55 volts.
Start engine, volts drop to 12.4 on batt 1.

Clearly the alternator is not charging - but could there be another solution - blown fuse or something, or can we assume the alternator is shot? My dealer installed this alternator in April of last year - shouldn't they last more than a year????

[chpthril]

It certainly sounds like the alternator is not charging. Here is what I would do next: With the ground lead of your DVOM connected to a battery ground, take the meters positive lead to the main post of the alternator and see if you are reading battery voltage. Should be the same voltage as your read when the lead is directly on the battery post. This will tell you if the entire electrical circuit is complete. A loose or poor connection on either a ground or the main B+ and you would see less voltage then at the battery. Next, start the engine and give it just a little throttle and see what the voltage is again off the back of the alternator. If the alternator is charging, voltage should be above the batteries static voltage level noted previously.

[Kimber]

Thanks Mike, I will try this today.

[OldeBoy]

To add to Mike's comments, you may want to check your connections for corrosion. I have had voltage/charging problems and did a lot of voltage drop testing with my voltmeter. It turns out I had significant corrosion on the alternator output connection that was dropping my voltage by 1.4volts. The output of the alternator was 14V at the alternator terminal. When I checked the connection between alternator and starter there was the 1.4volt drop. Since I fixed this issue it has made a huge difference for my second battery.

[25cents]

Just had a similar problem last week and it turned out to be one of the connections from the isolator. Couldn't tell it was bad until I cut back the red vinyl tape covering the crimped end. Anyway $7 part and everything is good again. Good luck and hope its not the alternator

[Kimber]

I haven't been able to look at it yet. Should be back from a fishing trip late tomorrow night, plan to look at it Sunday.