Alternator issues

[Helmsman]

My port alternator showed 11 volts on the gauge yesterday on a sixty mile trip. It showed 12 on the gauge with the generator running today on a 40 mile trip. I put a multimeter on it this evening and it is producing 13.7 volts. The starboard is producing 14.7. The battery charger was pumping amps last night indicating that it had some real charging to do.

Time to replace? Anything else I should check? The belt is fine and the alternator is spinning normally, just producing less voltage than the other.

Any thoughts would be appreciated!

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[tomschauer]

Do you have any other 12v load on the battery that is connected to that voltmeter such as an inverter? Maybe it is more than the alternator can keep up with?

Also, not sure how your batteroes are configured, but most likley that meter reads bank one or two, not the alternator. So if you have the engines running on bank one and the house on bank two the alternator are not charging bank two. Again, depending on your configuration.

[mjk1040]

Port Alt.is bad or has a bad regulator in it. Alt's should produce 14.5 volts.

[bud37]

If your boat is like mine, those dash gage readings depend on the position of your battery switch.....one engine feeds #1 bank and the other feeds #2....put your switch on both and you should see both gages operating properly. If the blower is running, it will pull it down etc.

When you test, check at the battery banks with only one engine at a time running and no accessories on, then add things and watch the dvm meter at the batteries etc....

[Helmsman]

Qr Bbpost Do you have any other 12v load on the battery that is connected to that voltmeter such as an inverter? Maybe it is more than the alternator can keep up with?

Also, not sure how your batteroes are configured, but most likley that meter reads bank one or two, not the alternator. So if you have the engines running on bank one and the house on bank two the alternator are not charging bank two. Again, depending on your configuration.

I have an inverter. I have had it since last summer. No problems until now. The alternators are 70 amp alternator. The feed goes to a ProIsocharge 130A x 4x Output isolator. The outputs feed the two engine batteries, a house battery, the generator, and the inverter bank of 4 6 volt batteries. I tested the alternator with that engine alone running. At the alternator it was 13.7 amps. At the isolator input it was 13.7 amps. The other alternator tested 14.7.

[Helmsman]

Qr Bbpost If your boat is like mine, those dash gage readings depend on the position of your battery switch.....one engine feeds #1 bank and the other feeds #2....put your switch on both and you should see both gages operating properly. If the blower is running, it will pull it down etc.

When you test, check at the battery banks with only one engine at a time running and no accessories on, then add things and watch the dvm meter at the batteries etc....

Good suggestion. Each of the four battery banks has a battery switch, so either on or off.

[darrenlife]

Did you have your blowers running at the time? Reason I ask the blowers have a high load and may bring your volts down

[Helmsman]

Qr Bbpost Did you have your blowers running at the time? Reason I ask the blowers have a high load and may bring your volts down

Yes, I had the blowers running. I will detach the cable from the alternator and test it. That way I will get a non-load voltage reading. I will also turn the battery feeds off to see whether one of the banks pull the voltage down.

[tomschauer]

if the alternator is putting out between 13.5 and 14.5 vdc, its ok. If you have your inverter running under load it may be taxing the alternators. Also, one bad cell on one battery could drag everything down. You may want to isolate and check each battery. I don't believe that is the factory configuration for that boat. If the isolator was improperly sized for the system or inverter, or not properly wired that could be your problem. If so be careful, they can tend to go up in smoke when they fail.

[Helmsman]

Qr Bbpost if the alternator is putting out between 13.5 and 14.5 vdc, its ok. If you have your inverter running under load it may be taxing the alternators. Also, one bad cell on one battery could drag everything down. You may want to isolate and check each battery. I don't believe that is the factory configuration for that boat. If the isolator was improperly sized for the system or inverter, or not properly wired that could be your problem. If so be careful, they can tend to go up in smoke when they fail.

Thanks, Tom. The isolator ( http://www.promariner.com/en/23127 ) and the inverter are both Promariner new units. I intend to check the voltage from the 70 amp alternator tomorrow all the way through to the inverter. I think that the problem lies somewhere there. When I get back to the dock and hooked up the shore power, the battery charger was pulling 16 amps based on the gauge on the panel. That seems high to me though the inverter battery bank was discharged to 11.7 volts. I suspect the batteries (4 6 volt batteries that are 8 months old) could also be the culprit. Will be crawling around checking everything tomorrow.

The isolator is 2 alternator 4 bank isolator. One alternator (port-the problem one) charges it’s engine (dedicated) and the 2000 watt inverter bank. The starboard charges its engine (dedicated) and the house battery. The generator charges it’s own through a separate charger and is not charged through the alternators. So, I will take the load off the port engine and check the alternator output, then hook it back up, check it, check the isolator in and out, the charge at the battery switch, and at the battery’s. I will also switch off the inverter batteries and check for a dead cell.