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LiFePO4 in new travel trailer

rlmesq

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Oct 24, 2021
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I'm planning to buy a new Gulf Stream Vista Cruiser 19ERD travel trailer in the next few months. My long range plan is to install solar panels with an all in one inverter/charger/controller sometime in 2022, but I'd like to start off with a 100 amp LiFePO4 battery.

What's the best way to handle this? I'd like to avoid buying a bunch of stuff I'll discard in less than a year. Would I have to buy a different charger to replace the shore power charger built into the trailer? Can the LiFePO4 battery still charge through the 7 flat trailer connector, or do I need a DC to DC charger? Or would it be best just to buy the all-in-one now and add the panels later?

Many thanks. Once read so many articles and watched so many videos that my brain hurts. I think I would be better equipped to install the full-blown system instead of just changing the battery.
 
Ok. So this is a complex topic involving voltage drop through the vehicle, wire ratings, fuses, alternators, etc....


In my experience you'll probably see enough voltage drop over the 7 pin that you won't need the DC charger to limit current.

It will charge the battery this way, but very slowly.

Also in my experience, if you have a smart alternator the tow vehicle will draw *from* the trailer battery when the alternator shuts off.
This can be resolved by turning on your headlights or using "tow mode" if your vehicle has one that keeps the alt on when towing is enabled, like my 1500 silverado.


Further to my experience, if your tow vehicle voltage exceeds 14.6v at any point (at the trailer plug, not under the hood) you risk the lithium battery triggering its over voltage cutoff, which shouldn't be an issue unless while driving and should reset when the tow vehicle is shut off. It won't damage it, but can be annoying if the reset delay is long.


The last two points make it clear that a DC to DC charger is the best solution but you need to absolutely ensure you don't exceed the tow vehicle's *wire* current rating, which may actually be less than the fuse.

For example my truck has a 40a fuse and a 14awg wire.

The way to be absolutely sure is to figure out what size wire you have in the vehicle, change its fuse to exactly its current rating (if it's too big a fuse, like mine), then hook up with a nearly empty battery.

Mine did not blow the fuse as it only pulls about 11a, so it's fine, but this must be checked with a low battery as the increased voltage difference may draw a lot of power.

If so, a dc to dc charger will serve to limit current as well, and may be an OK solution using the tow power wire itself, but installation gets a bit complex when putting it in the trailer itself in that you need to separate the incoming positive power from the rest of the trailer. Usually in a junction box somewhere.

You can resolve all of this by installing your own cable for the DC to DC unit, then you just need to be sure you don't exceed your idle output of the alternator unless the vehicle is smart enough to automatically increase engine rpm with increased alternator load.

Lots of if/then questions to resolve when using lithium.
 
I would just simply pull the fuse to the 7 pin and charge the LiFePo4 battery independently of the tow vehicle. The money for a DC-DC charger can go towards a solar system that will adequately charge your battery while you tow anyway.
 
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