Have you actually experienced your UMC heating up much? I charge at 40 amps, 240 V with my UMC and it gets only slightly warm on the cable itself, but not anywhere near hot to the touch. The warmest point I found was on the metal plate of the UMC near the green LED. I felt no noticeable warmth from the car plug or the NEMA plug end of the cable.
People’s descriptions of relative hotness are always going to be really subjective and hard to relate to other people in text. Mine is apparently not as hot as
@jerry33 is describing. It would not burn my hand or feel uncomfortable to hold for a while, but from working with and building computer stuff for many years, I know that heat and temperature cycling is the main thing that hurts electronics, and that box in the charge cable and the cord was feeling kind of warm.
I keep hearing people say, “It’s kind of warm, but not REALLY hot, so it’s fine.” But I look at the pros and cons of the situation. What do I gain by running it at 40A? Not a single thing at all. There is zero benefit to me in doing that. I’m going to be sleeping, so it doesn’t matter if it takes 2 hours or 3 hours during the night to recharge. But by turning down the current a little bit, it takes away that slight warmness.
Also, people forget that it’s not just how the temperature is while it is running. Materials stress (like the solder points on circuit boards or metal/metal junctions that expand and contract) are affected by cycles in how far the temperature MOVES and how many times. When the cable isn’t being used, it’s garage room temperature. When you use it, it heats up 20 or 30 degrees or whatever, and then goes back down that same 20-30 degree difference when it cools off. It’s doing that low/high/low cycle every single day. If I can make that cycle several degrees smaller, that is a bit less stress on the materials. It may be a very small benefit, but it’s something.
So I compare a small benefit to the materials with absolutely no difference to my charging convenience, and putting the current down by several amps is a net positive.
