Wire size from converter to battery

[Bub]

I have a 2022 Cougar 26RBS travel trailer. It came with Keystones basic solar package which includes 200w solar panel on the roof with a Victron charge controller. It has a WFCO 9855 converter and I have two 6v 210ah batteries wired in parallel. i am thinking about swapping to Lithium batteries and have looked at the pd9160alv converter from progressive industries. My concern is the wiring from the converter which is in the back of the trailer to the batteries in the front. It is about 25 feet and is wired with 6awg wire. Based on the charts I have looked at it is undersized. Is this a safety issue Or will it just cause a slower charge. I started looking at this based on research about lithium charging profiles and also what many refer to as a Simple remove and replace. Now I’m not so sure?:

 

[HRTKD]

As long as you size the converter to fit the wire gauge, it should be OK. Figure out the wire length and gauge and plug it into a wire gauge calculator to determine the voltage drop. Ideally, we want to see less than 3% voltage drop.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

A 25' length (50' roundtrip) @ 12 volts with 40 amps would have a voltage drop of 6.78%. That's more than we want to see. Use a converter with smaller amps or replace the wiring with 2 gauge to be under 3%. An alternative is to relocate the converter. 120Vac will have a lower voltage drop over that distance than 12 volt DC will.

 

[Bub]

Thank you Jim. Appreciate the quick response. And to be sure lead acid vs lithium really has no bearing here. I should fix it one way or the other. This was how the RV was delivered!

 

[HRTKD]

They don't make RV's like they used to. Cutting corners seems to be the norm. On my RV, the cable from the battery on the tongue to the main distribution panel was only 8 gauge. But they didn't expect there to be an inverter and higher capacity converter, so 8 gauge was reasonable.

If there is any chance that you're going to put in an inverter, consider ditching the converter and installing an inverter/charger instead of just an inverter. That cuts out the converter altogether and makes for a less complex system.

 

[Bub]

Thank you for the info. I actually had an inverter installed when I purchased so spent a lot of money on it already. I see where you’re coming from though. I think maybe looking at the location of that inverter might make the most sense.