Low alternator voltage

[Radhearn]

I have a 480 Sedan Bridge with Cat 3196's. I just got the boat and the port alt was reading a little less than 12. I replaced it, but it did not help. Now the Starboard alt is doing the same. When in gear the voltage drops to 11-11.5 and is causing false alarms on the monitoring system.

Has anyone else ever experienced anything like this?

[Four Suns]

Have you checked your batteries? How old are they? They have water in them?

You only need to post your question in one spot BTW.

[Radhearn]

Thanks. I'm a new member. Yes, the Bats are all good.

They all load tested and electronically tested as good.

Someone here said it could be the isolator. What exactly is that and does anyone know how to test it?

[fc3]

First put a known good voltmeter on the batteries and check the engine running charging voltage. The other stuff is just too inaccurate to trust.

Best regards,
Frank C

[Nehalennia]

Thanks. I'm a new member. Yes, the Bats are all good.

They all load tested and electronically tested as good.

Someone here said it could be the isolator. What exactly is that and does anyone know how to test it?

Hey Rad,
Also, stick your boat's info in your Signature. It helps us know what you have and can help us help you.

Welcome aboard.

On My old boat I had thought my Alternator had gone south, but it turned out it was the batteries. So double check them as Frank stated.

Best of luck

[JVM225]

Isolater is inside the Alternator.
I agree with checking the batteries with the engine running. Dash gauge could be off.
You may also want to spray a little contact cleaner on the terminal on the back of the Alternator.

[fc3]

Isolator is external to the alternator. It's on the bulkhead somewhere, if the boat is so equipped. Might look like this one (http://www.onlinemarine.com/online_superstore/electrical/guest+2430+battery+isolator.jpg), but probably with 4 terminals. Could be any color. Mine is anodized gold.

Best regards,
Frank C