Originally Posted by Canadian Eh
I am in the process of switching over to Lithium batteries. I have the charge controller and need to add a DC to DC converter to the alternator. Considering the size of the E450 I was surprised at how little firewall or fender space there is to mount one.
I see one extra #4 wire going into the battery box but I'm not clear on how the charging system works. How can I tell which lead is coming off the alternator to charge the house batteries.
When you install a DC-DC charger you don't want to connect to the alternator but rather to the Pos and Neg terminals of the Starting Battery.
The DC-DC charger will draw it's power directly from the starting battery and the alternator will provide current to both battery and charger.
Depending on the manufacturer of the DC-DC charger their install manual will show proper connection as well as fuse locations and sizes for both wires from the Starting battery and to the house batteries.
The DC-DC charger does not need to be mounted under the hood and can be mounted near the house batteries (mine is mounted inside my TT right next to my Battleborn batteries) as long as the wire from starting battery to DC-DC charger is large enough (again, it's in the manual).
Don't worry about fan noise if you mount the DC-DC charger in or close to living space. Fan only runs while driving (or engine running).
By connecting directly to the battery (Negative cable, not using chassis ground) any current sensor used to monitor charge of starting battery will still function properly and house batteries won't be starved of charging current once starting battery is full. Connecting both Pos and Neg to the battery lets the current sensor and house batteries as one and will keep current flowing until both are fully charged.