Battery & electrical questions

SJ-Chris wrote:

coolmom42 wrote:

*Does the chassis alternator charge the house battery? If so, how well?

Almost every RV is set up to allow the chassis alternator to charge the house battery. (it's a beautiful thing that comes almost for free).

I have a 2015 Thor Majestic 28a...In my experience, the chassis alternator does a great job charging the house batteries. I have a battery monitor on my house battery bank. When the house batteries are at ~50%, I have seen my chassis alternator pumping 50+ amps into my house batteries when the engine is running (even just idling).

-Chris

Chris ... the same here.

Our Class C's Ford alternator boost charges our coach batteries very well. I often just idle the V10 engine for awhile at a campsite to partially charge the house batteries. It idles very quietly and with no vibration felt inside the coach - unlike V8 powered trucks I've owned in the past. Other nearby campers should not be able to hear it running when I top up the batteries this way because we can hardly hear the engine idling when we're in camp right beside it.

I have a digital ammeter mounted on the dash that shows current flow into and out of the coach batteries, and I've seen up to 70-75 amps from the alternator going into the large AGM coach batteries with the engine idling. A complete charge of the coach battery bank by the alternator takes about three hours when driving. When the ammeter on the dash shows the coach batteries accepting only around 1 or 2 amps with the engine running, I know that the coach batteries are fully charged.

Our first motorhome (a 1969 model built on a GMC chassis) was bought from my father-in-law and for years that was his only way of charging it's coach batteries when drycamping. He thought nothing of just idling it's gas V8 engine for awhile each morning.

Now ... what has happened twice in 15 years regarding our current motorhome's batteries getting charged by the Ford alternator ... is this: The 12V solenoid that connects the engine alternator to the coach batteries whenever the ignition key is turned on has failed, such that we arrived at our destination with coach batteries that did not get charged by the alternator.

This above situation was probably due to corroded contacts of the solenoid - because I could still hear the failed solenoid engaging when I would turn on the ignition key. I now have an after-market heavy duty 12V solenoid with silver plated contacts inter-connecting the engine alternator and coach battery bank.

I also have digital voltmeters on the dash for showing both the terminal voltage of the coach battery bank and the voltage on the chassis 12V system. If these meters ever DO NOT show nearly the same voltage on both systems (i.e. 12.XX volts on the coach batteries, but 13-14.XX volts on the chassis system) with the engine running ... then I know that either the inter-connect solenoid has failed to engage, or has highly corroded contacts -> and that I'm going to arrive at my destination with coach batteries that haven't been charged while traveling.