Yesterday was along, hard day of working on the RV.
I'm upgrading the RV to have Lithium "house" batteries instead of the original lead acid batteries. Our RV has two types of batteries, the "house" batteries, which run out lights, fridge, TVs, etc., when we're not plugged into an exterior power source. The other battery we have is the "chassis" battery - identical (but larger) to your car's battery. The chassis battery starts the engine and runs the headlights, etc., when we drive.
The house batteries the RV came with were pretty much toast, so after some thought, we decided to move toward the lithium batteries and make preparations for adding solar panels.
Installing lithium batteries means making many changes to the RV. First, it means building a new battery bay, because the old battery bay isn't big enough for the new batteries. Additionally, the lithium batteries won't work in freezing temperatures. Unlike lead acid batteries, the lithium batteries can be installed in an enclosed space, so that helps in keeping them warmer than freezing.
I started by cleaning out a storage bay. Finding new, permanent homes for most of that stuff shouldn't be too hard. The next part was to build a frame to support the weight of the batteries. The floor in the original battery bay was made with steel. The storage bays have plastic floors, so the wood base will do well to spread out the weight of the two batteries, and help to keep them corralled.
The next step was to install the DC/DC charger. This is something unique to using lithium house batteries. When the engine is running, and we're driving, the house batteries get linked into the same circuit as the chassis battery, and the alternator for the engine charges ALL of the batteries. Lithium batteries, however, can take a much higher charge than the alternator can provide. This reportedly would kill our alternator! So, the answer is to install a DC to DC charger between the chassis battery and the house batteries, and eliminate the old circuit for charging the house batteries.
With the DC/DC charger installed in the new battery bay, the next step was to install fuses into the circuit to provide protection for the system.
The next step was to climb under the RV and run conduit for where the new battery cables will go. One run will go between the new battery bay and the old one, to link the circuits so that the RV can still have power. The other cable will go to the chassis battery. I spent a while on my back, crab crawling under the RV running conduit and securing it under the RV.
The next part was to run the cable through the conduit. I call it cable, but it's 2/0 wire. The wire itself is about the thickness of a finger! This think wire is necessary to help.make sure that the wire doesn't overheat, and also to limit voltage drop in the line. DC current doesn't transmit as well as AC current (used in your home) so as much as possible I want to limit the amount of high amperage DC wire runs to limit the potential voltage drop.
After all of that was done, I started losing daylight. The batteries are in the bay with the DC/DC charger, but nothing is wired up yet. The next time I work on this project will be to finish securing all of the conduit inside the left front wheel well, and the engine compartment. I'll also start wiring in the new house batteries (and disconnecting the old ones). The last part will be to install the new charger/inverter, which will help to charge the house batteries when we're plugged in, and will convert the 12 volt DC power in the batteries to 110 volt AC current (like in your house), and remove the old charger and inverter.
I'll probably need another full day to finish the whole project. I need to have everything at least buttoned up enough to drive before we leave Wompatuck on Friday.