100A 12V Cheap (everywhere but the wallet... ok so 20 bucks... lol) auto parts stores disconnect switches...
Started getting hot and developing between 300 and 400mV drop in the 30 and 40A range. Decided to see what the problem was, expected to find oxidized contacts or evidence of sizzling... Nope, just cheap!
The bridge bar is about as thick as a US nickel... couple mm or so. Didn't measure it exactly. Anyhow, it's slightly curved back away from the target contact plane and as you can see, just rubbing really small spots toward the plunger. A simple extruded bar of copper.
... and a closeup of each side...
Then there's the target contacts... They look to me like they were extruded as well, but along the stud axis, with no milling, doming, or possibly even just looked at for a half second with wishful thinking in mind... Absolutely nothing done other than whatever was involved in creating the threaded studs on the other side.
Couple of close ups of those...
I've got 2 more of these things in the mix, just "heavier duty"... supposedly good for 300A. I shiver at the possibilities with just one early system stress test where I was in the ~150A mark for a less than trivial amount of time (again, not thru this particular one, but the others aren't THAT much different).
Moral of the story... save the headache that 20 bucks buys at your local auto parts store (or possibly worse, online), and cough up a few bucks for a real switch... at the very least, one with wiping action in some form... All exercising these things does is make them worse.
Steve