Alternator Charging of Lithium Iron phosphate on a travel trailer

[12VoltInstalls]

Since the distance from alternator to trailer connector to battery, voltage/amps at the trailer battery will be less than at the truck battery. However, the lifepo battery does have different ‘expectations’ than a lead acid battery for charging. You can use the existing truck feed and drop a DC2DC charger in line right at the trailer battery.

In your case you mentioned you don’t need the truck recharge anyways. So pulling the fuse is an option. A lifepo-compatible charger is a fraction of the cost of the lifepo battery though.

I don’t see why you couldn’t just depend on solar as you stated. But the ‘cost’ of vehicle charging to the trailer is basically nothing after you by the DC2DC so why not? Fully charged is ready. Drive it use it for a while with the fuse pulled. If you wind up needing vehicle charging you know what to do.

 

[Scycle]

I have a '21 F350 6.7 diesel and soon changing my one FLA with two lithium and been researching the same issue and have gotten mixed responses and since I am new at this, leaves me undecided about what to do. I don't plan on relying on the truck to charge the batteries but would be a nice backup, but don't want to spend a bunch of $$ and do wiring on that right now. I want to get the 5th wheel setup with new batteries, battery monitor, and a way to charge those batteries keeping on mind that I would like an inverter and some solar to start.

 

[HRTKD]

I have a '21 F350 6.7 diesel and soon changing my one FLA with two lithium and been researching the same issue and have gotten mixed responses and since I am new at this, leaves me undecided about what to do. I don't plan on relying on the truck to charge the batteries but would be a nice backup, but don't want to spend a bunch of $$ and do wiring on that right now. I want to get the 5th wheel setup with new batteries, battery monitor, and a way to charge those batteries keeping on mind that I would like an inverter and some solar to start.

The critical piece of the trailer/truck circuit is the breakaway brake system. If you disconnect the new LiFePO4 battery bank from charge circuit coming from the truck you won't have any power going to the those brakes. However, it depends on where you disconnect the circuit. If you follow the 7-pin cable into the initial distribution panel (usually toward the front of the trailer - this is not the main distribution panel with AC and DC) and disconnect the 12 volt charge coming from the 7-pin cable to the main distribution panel then the breakaway system should still have power.

A DC-DC charger is a one way circuit. If you put the DC-DC charger between the initial distribution panel and the LiFePO4 battery bank then the breakaway system does not have power.

My RV trailer's LiFePO4 battery bank does not need a charge from my truck. I disconnected the charge from the 7-pin at the main distribution panel. I chose to leave a small lead acid battery on the tongue that does get charged from the 7-pin. The breakaway system gets power from that battery. The on-board generator also uses the lead acid battery for starting. My Multiplus inverter/charger will provide a low amp trickle charge to the tongue battery which also has it's own solar panel. It's like I have two separate systems.

The simple solution is to install the LiFePO4 batteries as if they were a set of lead acid batteries and don't worry about the issues that may bring about. Ignorance is bliss and it's initially less expensive. Long term, it could be expensive if you trash your LiFePO4 batteries. I wasn't comfortable with the charge profile that would be coming from the tow vehicle, so I had to do something.

 

[grizzzman]

I have a '21 F350 6.7 diesel and soon changing my one FLA with two lithium and been researching the same issue and have gotten mixed responses and since I am new at this, leaves me undecided about what to do. I don't plan on relying on the truck to charge the batteries but would be a nice backup, but don't want to spend a bunch of $$ and do wiring on that right now. I want to get the 5th wheel setup with new batteries, battery monitor, and a way to charge those batteries keeping on mind that I would like an inverter and some solar to start.

Your truck likely has a “smart alternator system” with that said if it does your LFP will trickle charge the trucks AGM battery (like mine does). I suggest testing the voltage on a trip to test this. (In my case I found a way to defeat the charge control)