Originally Posted by Gringo
really? I am confused on this. I had tried a couple times in the past to turn the Use/Store switch to off, and the light would never go out no matter what I did. so I have no easy clue whether it was in Store or Use mode.
I read in the manual that the batteries would always charge if plugged into the tow vehicle. Is this not the case?
The light can be confusing. When plugged into shore power the light will be on whether the switch is in Use or Store. The switch does operate the relay and in Store, the batteries are disconnected from the converter regardless of the state of the light. Without shore power, the light is is off in Store and on in Use.
I've not explored what happens with the light if connected to the TV and its alternator is providing power to the trailer.
As to your question about charging from the TV, my short answer is Yes, No and Maybe... If this is the factory harness provided as part of the towing package, it is typically fused with a 30A fuse or better and hopefully it is at least 10 gauge. There is often a relay on the line that provides the charge current only when the engine is running, this is to prevent accidental drain of the starting battery when parked should the trailer continue to put a load on the TV electrical system. The fuse and relay are possible failure points that can go unnoticed. In some cases, the relay isn't installed on the assembly line and the user doesn't understand why the batteries are not taking a charge going down the road. Since your truck was giving you power to run the furnace, you're good there.
Primarily due to the wire gauge and length, the charge current available to the batteries from the TV is limited. The bottom line is that if you ran your house batteries down then headed down the road for a few hours, there would be some charge on the batteries, but I wouldn't expect them to be fully charged.
In my case I discovered after I bought my trailer used, the charge line from the the trailer plug was not connected to the batteries! The trailer came from JC with the ActiBrake actuator. It was replaced with a Dexter actuator under warranty when the PO owned it. I have to assume there was a change in the wiring at that time and the needed wire was omitted. The schematic for the Dexter unit showed a connection to the umbilical that wasn't there. After I put one in, everything worked as advertised.
The best way to verify that your TV is charging the house batteries is to connect a voltmeter to them then start the TV and the voltage should go up.
A fully charged Group 24 battery in excellent condition can provide about 70 Amps of power (double that for a pair). My furnace draws 7.6 Amps while running. The circuit boards for the fridge and water heater also draw from the batteries, and there are the lights, water pump... All the little things add up. In cold weather the furnace runs a lot.