Size of Alternator
I have a class B with 1 engine battery and 2 house batteries. I also have a 120-12volt Norcold fridge. My engine alternator is 75 Amps. It says that the fridge on 12v draws 4.0 amps. My house batter...
Forum Discussion
I've had the same situation twice (years apart) in our Class C ... of the coach batteries hardly getting charged when driving ... and we have a 130 amp alternator.
Both times it was caused by the automatic solenoid that connects the coach batteries to the alternator. This solenoid is closed when the ignition key is turned on to run the engine. The contacts in the solenoid over time get corroded contacts such that they still allow some current to flow but with a voltage drop across the contacts due to the corrsion. This voltage drop across the contacts means that the coach batteries are not seeing the high voltage that the alternator is putting out and that the engine starting battery sees.
I now have two digital voltmeters on the cab dash. When traveling, one shows the voltage on the engine starting battery and the other shows the voltage on the coach batteries. Whenever the coach batteries have a lower voltage on them than the engine starting battery, I know that the solenoid that connects the coach batteries to the alternator has contacts that are beginning to corrode. This means it's time to replace the solenoid so that the coach batteries get charged like they should whenever the engine is running.
Both times it was caused by the automatic solenoid that connects the coach batteries to the alternator. This solenoid is closed when the ignition key is turned on to run the engine. The contacts in the solenoid over time get corroded contacts such that they still allow some current to flow but with a voltage drop across the contacts due to the corrsion. This voltage drop across the contacts means that the coach batteries are not seeing the high voltage that the alternator is putting out and that the engine starting battery sees.
I now have two digital voltmeters on the cab dash. When traveling, one shows the voltage on the engine starting battery and the other shows the voltage on the coach batteries. Whenever the coach batteries have a lower voltage on them than the engine starting battery, I know that the solenoid that connects the coach batteries to the alternator has contacts that are beginning to corrode. This means it's time to replace the solenoid so that the coach batteries get charged like they should whenever the engine is running.
