I was charging a car battery in situ using my bog-standard B&Q
extension reel on Saturday and its thermal cutout tripped. The
charger was giving about 4 amps, which makes it about 50W. I had
always presumed that the thermal cutout would trip because of high
current passing through it, but am I missing the point? It was quite
warm and it may have got a bit warmer than you would expect in the
car, but I was a bit surprised. It reset OK and worked later on with
a drill. I just wondered whether some of the experts in these things
would know whether it's something trivial (too warm in the car, faulty
trip etc) or whether I'm just misunderstanding how these things work.