After much stumbling around and a couple of phone conversations with John at RV Custom Products, as well as downloading and reading Ed Felker's excellent Thor Axis/Vegas manual I decided to skip the DC2DC charge controller in favor of upgrading the alternator. I installed a shunt and amp/volt/charge meter and will be able to see how many amps the alternator is trying to put into the lithium battery. If it looks like the alternator is working too hard, which it will be if it is the 120 AMP one, I'll go to the 225 Amp alternator - problem solved (I hope). Ford's price for the OEM part is very competitive.
Look in the compartment under the drvs seat. If there is a black box with a lot of fuses and battery cables going to it, you have an RV Custom Products BCC
Here is the Battery Control Center Schematic we have in our older Axis/Vegas:
https://rvcustomproducts.com/th-1020
The "troubleshooting guide" gives a lot of information
Ford make three different alternators for the E350 chassis with the 6.8L engine, a 120 Amp, 155 Amp, 195 Amp, and a 225 amp
https://www.varsityfordparts.com/v-2...al--alternator
Without being able to look at the tag on the alternator (long mirror and a flashlight after taking the air cleaner assy out?) out Thor's could have any one of the three fitted, depending on what Thor spec'ed.
Thor Forums
