enblethen wrote:
Engine on, the solenoid clicks, and the alternator charges the house batteries
Just because the solenoid clicks when the engine is running does not mean that the coach batteries are getting charged very well from the alternator.
In 10 years, I am now on our 3rd battery boost/charge solenoid in our Class C motorhome.
The solenoid can click into engagement alright, but with lower than normal alternator output voltage being applied to the coach batteries' terminals. Lower charging voltages seen by the coach batteries means that they may be charging slower than they should be - if much at all while traveling down the road.
With current flow over time the solenoid contacts oxidize/corrode over time such that the contacts present high resistance to current flow. During current flow, this high resistance reduces the voltage that gets applied to the coach batteries' terminals.
You can check the condition of the solenoid's contacts by measuring alternator output voltage with the engine idling and then also measuring the voltage on the coach batteries with the engine running. If these two voltage readings differ by much, then the solenoid's contacts are compromised and you will find that between camping sites the coach batteries aren't getting brought back to a full or near-full charge.
I have permanent voltmeters mounted on the dash in our Class C, so that I can see alternator output voltage and voltage on the coach battery terminals both at the same time whenever the engine is running. If these two voltmeters always read very close to each other than I know that the coach batteries are getting charged the best that they can be by the alternator and that hence, the boost/charge solenoid is both .... engaged .... and has contacts that are still in good condition.
