I see a couple things in your pics:
First is the temp controller that it looks like you are using as a cutoff contractor to (from?) your 36V-12V converter.
I don't think these are meant to handle that many amps. I was using one for a couple years to run sead tray heaters and it stopped working on a 5A load yesterday. I added a 100A digital contractor and it works great (surprisingly).
Try taking the temp controller out of the equation (take the 2 left wires and twist them together) to identify or rule this out.
Probably not related to this issue but if this breaker gets warm or trips before it should, replace it with a quality breaker immediately. Otherwise replace it soon, its going to be trouble with a 1500W inverter (sooner than later).
What brand is this? $15 Chinese knockoff?
