Charge agm trailer with lifpo4

[Joe Sr]

In a case where there is too little sunshine during a week of mountain boondocking, I would like to be able to charge my agm trailer battery using my separate lifpo4 battery-in-a-crate system built a'la Will's videos. Is there any reason I can't do that, say, by using an anderson connector that is wired into the trailer system through a fused circuit in the main trailer dc panel? It's a Casita and there is no room in it to consider the usual alternatives.

 

[Bobert]

In a case where there is too little sunshine during a week of mountain boondocking, I would like to be able to charge my agm trailer battery using my separate lifpo4 battery-in-a-crate system built a'la Will's videos. Is there any reason I can't do that, say, by using an anderson connector that is wired into the trailer system through a fused circuit in the main trailer dc panel? It's a Casita and there is no room in it to consider the usual alternatives.

If it works it would take forever and you will have at least 20% losses in the process

 

[WYtreasure]

In a case where there is too little sunshine during a week of mountain boondocking, I would like to be able to charge my agm trailer battery using my separate lifpo4 battery-in-a-crate system built a'la Will's videos. Is there any reason I can't do that, say, by using an anderson connector that is wired into the trailer system through a fused circuit in the main trailer dc panel? It's a Casita and there is no room in it to consider the usual alternatives.

I would opt to disconnect the AGM and plug in the crate, while there is no load on the system.

My thoughts don't charge the AGM, but would keep you going in your Casita.

 

[Joe Sr]

WYTreasure: I was originally thinking in those terms, then began to wonder why I really need to disconnect the agm. It's still not clear to me why it should matter and why, at 14 volts, the lifepo wouldn't just share the load and also charge the agm (my solar successfully charges the agm at 13.5 to 14.5 volts). All the power would still be there with very little loss.

 

[12VoltInstalls]

why, at 14 volts, the lifepo wouldn't just share the load and also charge the agm (my solar successfully charges the agm at 13.5 to 14.5 volts).

Because the AGMs do not accept 100% of the charge; they will not keep all the amps
Plus once the LiFePo drops a bit of voltage the charging will become less effective and you’ll then have two partially discharged batteries.
It’s not like pouring a two gallon jug into a one gallon jug. With electrons there is always going to be “spillage” where you wind up with less than you started with.

A) switch from one battery to the other
B) a small horizontal shaft HF gasoline motor with an 80A GM one-wire alternator driven by the little motor

 

[WYtreasure]

WYTreasure: I was originally thinking in those terms, then began to wonder why I really need to disconnect the agm. It's still not clear to me why it should matter and why, at 14 volts, the lifepo wouldn't just share the load and also charge the agm (my solar successfully charges the agm at 13.5 to 14.5 volts). All the power would still be there with very little loss.

Someone smarter than me will have to explain why the AGM & LiFePO4 don't do well together. 12VoltInstalls reply is good enough for me.
Mixing batteries of different composition just seems wrong in my head.

 

[12VoltInstalls]

have to explain why the AGM & LiFePO4 don't do well together

That wasn’t a factor in the question nor in my answer.

 

[timselectric]

Actually mixing AGM and LiFePo4 batteries, is the exception to the rule of not mixing battery types.
Because, they have similar charging profiles.

My suggestion would be to parallel the two batteries from the beginning. And you will have the total capacity to work with.

 

[Joe Sr]

Paralleling the batteries is not an option because of space. I'd hoped I made that clear.

 

[timselectric]

Paralleling the batteries is not an option because of space. I'd hoped I made that clear.

How did you plan to charge batteries, then?
I didn't see any mention of a DC to DC charger.
Maybe I mistakenly assumed that the Anderson connector was going to be making a parallel connection?

 

[acdoctor]

Leave the AGM’s at home.

 

[Joe Sr]

tims: I charge them with separate (and usually separated) panels and controllers, and yes, the anderson will connect in parallel. I'll bring the crate into the trailer when I need it and temporarily hook it up.

 

[timselectric]

Ok, that was my understanding.
My suggestion was to bring in the crate battery, when you expect to be needing it. And then use both as needed. On a temporary basis. Whenever you think you will need the extra capacity.

 

[timselectric]

If you set up the Anderson connector, on the outside, you could hide the crate battery underneath the RV. And if the SCC and panels are portable, use them also at the same time.

 

[Joe Sr]

Part of the reason for the Casita is the integrity of the fiberglass boat-like hull and I don't want to put anymore holes in it to create potential leaks (important when you travel on gravel and less roads -- if they can leak, they will). Also; if I were to make a hole, I'd use a waterproof sae like the one installed by the factory for the on-board solar connection.

Thanks for your help.