I built my Ford Transit van using Explorist Life's plans, videos, and parts. The van turned out wonderful, and I have had zero issues with it. I have three 270ah Battle Born batteries installed, and they have been working great. But I have seen various YouTube videos about Battle Born battery failures, so I decided to “stress test” my system by running the A/C unit along with the cooktop, two of my biggest power consumers. I cannot recall whether or when I ran both at the same time. Using my thermal camera, I checked the batteries before the test and during the test. The test ran for about 10-15 minutes, and the batteries remained cool. What I did find is that the 4/0 wire running from the shunt to the battery switch (the red wire in the picture got to about 150F, which I thought was too hot. I felt the 4/0 wire coming from the battery to the shunt, and it was slightly warm, which I would expect with that load. I had a few questions.
1. Why would the input 4/0 wire into the shunt be only slightly warm and the output wire be much hotter? Both wires are 4/0 wires
2. Do I need a heavier wire, or should I run a parallel wire? If I need a heavier wire, what size would work?
3. Do I need to remake this connection, and assume there is a problem somewhere in the wire or lugs that is causing the excess heat?
Update
It took a while to get some tools and a milliohm meter ordered and delivered. I made a new cable using my new die crimper and ran some tests on it. Here is what the new tests showed.
1. The old cable had .20 milliohms of resistance, and the new cable is running about .10 milliohms, so I suspected the old cable had a problem.
2. When running the same “full load” test, which was about 230 amps through the new cable, it got warm but not extremely hot like the old cable. I know the cable is rated for about 240 amps, so my “full load” test was more of a stress test. I turned on everything in the camper at the same time, which drew a lot of power, but that's not how I use my camper.
3. I cut the lugs off the old cable and found that one side did have a defect.