Ammeter to Voltmeter...who does it?
From everything you posted earlier, it sound like it works like this.
When parked, the coach batteries supply the motorhome. There's no connection to the engine and cab electric.
Correct.
When the engine is running, the alternator recharges the battery. The alternator is wired the main charging circuit at the battery. That's probably why the ammeter showed 25 amps charging.
Yes, the alternator charges the chassis cab battery and a wire runs from the chassis cab battery to the 12v switched battery isolator solenoid, which allows the coach/house batteries to be charged, but only when the engine is running.
So the question is what equipment attached to the coach batteries would be running while the engine is running? Additionally, is that equipment regulated to 12.5 volts or will it see the system voltage from the alternator.
Everything in the coach uses 12V, water pump, lights, heater fan and stove exhaust fan. The fridge is 3-way; 110V/12V/Propane. Ideally, you want the fridge running on 12V, when you're traveling. There have been reported instances of people running their fridges on propane, pulling into gas stations, and the flame heating the ammonia fridge ignites gasoline vapors around the pump. The only thing I can really see running on 12V, while we're traveling, would be the fridge and maybe the LED ceiling lights, if the wife needs to use the bathroom or make us a sandwich.
Your existing wiring looks like 8 ga or heavier.
I had to refer to my Service Manual, to refresh my memory. The red positive battery wire to the starter relay is 6ga.; the red positive battery wire to the fusible link is 10ga.; the black negative wire to the engine ground is 4ga.; the black negative wire to the firewall body ground is 10ga.; the black alternator wire to the bulkhead connector is 10ga.; the red fusible link to the bulkhead connector is 14ga.
Routing it more directly as you illustrated maks it less likely to damage the connectors and ammeter, but still could cook the batteries. An alternator that produces more power at idle will keep the batteries from getting drained if the engine is running. But it will also be able to send more current to a completely drained battery.
And sending more current to completely drained batteries is what will cook them, correct? If this is the case, what I would need is some way to shut the flow of the current to the coach/house batteries off, when they are charged, and then open the flow of current, when the batteries fall below a certain voltage.
As far as monitoring the charge to the coach batteries, Aircraft Spruce, Jamestown Supply and other places have remote shunt ammeters.
The Power Distribution Center has an ammeter, allowing me to monitor the charging of the coach/house batteries.
