Engine voltage reading

[dennis41]

Boat: 2016 C 30 CB. My engine voltage reading has dropped to 11.2 to 11.9, and the little red battery symbol on the Garmin is on. I know this is bad, but I don't know what all this is really telling me. House batteries (Universal) going on 3rd season, thruster battery is new (Universal), start battery (Northstar) going on 4th season. Could it be a bad alternator?

 

[BB marine]

I'm not sure what is going on based on the information given. The Volvo EVC panel will give a readout of engine battery voltage. With the engine running the voltage should be @ 13Volts and climbing as the engine runs turning the alternator for charging. The alternator should advance the charge to as high as 14.7 volts. The batteries are fully charged. The Garmin is normally powered by the house battery bank. Meaning the voltage shown is the house bank. When the engine battery reaches 13+ Volts the ACR closes and parallels the house and thruster banks, charging theses banks too. All battery voltage readings with the engine running should be above 13Volts. With the engine not running all banks should be separated and should read 12.7 Volts when charged and when discharged around 12.3V. Any voltage reading below that would indicate the battery capacity is close to 50%. If there are several users, refrigerator, lights, water pump running it is not uncommon to see a voltage reading of 12.4 or 12.2 but then as the users turn off the voltage will rise. The best way to monitor a battery bank in a boat is by using a battery monitor instead of battery voltmeter.

If you engine battery is at 11.2 to 11.9 Volts it probably does not have enough capacity to start the engine. My advise before jumping to replacing an alternator is to charge all the battery banks fully. Take the charger off and let them sit for 1/2 hour then load test. If all batteries test to 80+% then start troubleshooting the charging system. Confirm that the engine battery is getting a charge from the alternator.

 

[Ralf H]

Hi Dennis,

Brian pretty much said it all. You'll need to do just a bit more diagnosis as Brian has described. If you follow his instructions you should have the answers you need. Remember, the most important thing is to know if the batteries can all be charged. If so, then the issue might be with the charging system (if there is no draw down like Brian articulated) and if not, then you should be able to isolate any bad battery. Hope this helps get you started.

Cheers,

Ralf

 

[dennis41]

Brian & Ralf - Thanks so much for the electrical advice & encouragement. I will disconnect & load test each & every battery. I still believe the Northstar start battery & the new UPG thruster batteries are good. I can't believe the alternator is bad either. I do intend to get to the bottom of this frustrating electrical mystery.