A DC-DC/MPPT is NOT just a SCC (Solar Charge Controller) It has the combined functions of a DC to DC battery charger and a Solar Charge Controller in one device. It is not an Apple to Apple comparison.
???????????
Do you have a vehicle with a Positive ground?
In my case, if I had to buy all the parts new, I would do this. But I would use Anderson SB series connectors for it. I'm using 120A Powerpoles for my big connections to my charger, because I got them for a steal. All my small 12V connections will be Anderson PP of the 15-30-45A variety, like most of Ham Radio has switched to. My main system will be in/on my pickup, including my fridge. When/if I get a trailer, I may put a separate solar system on it and build another LFP battery, too.
Well, you have to choose a safe route that will not subject the wire to physical damage or excessive heat. Check out routes used by other wires between the engine compartment and inside of vehicle. In the end you have to make a hole and route the wire thru it, protect the wire from abrasion at the vehicle penn point. Seal the hole with the wire in it for water and fire/smoke/exhaust fumes. This is where a friend (mechanic, vehicle audio guy) can help you learn something in exchange for a beer. Make sure the wire you install is large enough for the amps you need to flow thru it. Check out wire gauge tables for max 2-3% voltage drop for the length of your circuit (round trip length) or when you learn more, you will be replacing the wire.
They make PPs for the larger size, too. I have them in the 120A size for my starting and house battery connections to my DC-DC/MPPT and 75A ones for the Solar to it. I bought a bunch of pairs of the different colors for the small ones. Like, I'm using Blue/Black for my fridge. I would use Red/Black/Green in the small ones, for a circuit that used that pattern. I think I may use the Green ones with 10AWG for the "case" ground from my charger. It has 3 Negative terminals and a separate "Case" ground point. I'm making my whole setup "Modular" so I can pull the House battery and the charger out and leave plugs for all the main connections. The whole Negative/Ground side is going to be connected to one big bus bar, unless I find a good reason not to.
Just a SWAG, I can set my BMS to cut off charging at 14V/3.5V, but if I had a load on the system, I think the charger would send voltage for that load. At least that sounds logical to me. But I'm not an expert on this charger.
I have had the same experience. Charges at 14.37 volts continuously. I don't think this is good for the LiFePO4 battery. So I just turn the solar off once the battery is at 100 % SOC, manually.
If your engine is running, you'd have the same problem.
Engine not running, starting battery isolated from Renogy device.
The device should perform this control routine.
