With that in mind I thought I would try again to find a schematic of the Kingpan chargers that I am using. I found a thread on Endless-sphere that (somewhat indirectly - I can't figure out now how I found it) pointed to a site in Europe where a guy (thanks Albert) had reversed engineered some other brand of charger based on a TL494 chip (my favourite PWM controller).
I grabbed the circuit, pulled the lid off one of my spare chargers and - guess what - yes they are practically identical. There are a few resistor values that are different but just about everything is the same. It was relatively easy to devise a small daughter board that used the Op-amp that was driving the transition of a bi-colour LED on the charger to trigger the changer to cut it's current from 3A down to 180mA. The challenge was to be able to do the modifications without having to remove the main PCB from the case - with all the complications of re-seating power devices on heatsinks. I found that the best was was to remove one resistor and solder on four wires to a daughter board. The daughter board is circled in red. The heatshrink gets cut down, shrunk, then glued to the nearest strong component. I'll improve that toroid's mounting too - while I have the Sikaflex out.
I don't have to do all the chargers at once, just as I get around to them.
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