The series regulator MOSFET in our Solar Panel Controller overheated on our trip to Cape York after I had doubled the capacity of our panels from 100 to 200 watts. Its solder joint melted, it slid down from its pad on the printed circuit board and no longer worked.
I strung together a temporary alternative using a couple of transistors and an automotive relay which worked fine for the rest of the trip, although Janet did complain about the clicking of the relay every time the controller turned on and off. There’s just no pleasing some people.
When we got home, I took the transistor off the PCB and fitted 2 of them in parallel (to spread the load) on a separate copper heat sink and reconnected them back into the circuit. Due to the high thermal conductivity of the copper sheet, to solder the tabs of the transistors I used a heat shunt (pair of pliers) to hold the transistors on the copper sheet and a small gas torch to apply heat.
A small PC processor heat sink was bolted to the rear of the copper panel to provide additional cooling
The assembly was reinserted alongside the original controller PCB.
This modification should allow the controller to managed at least 300W of panels should we ad any more in the future.