Update - it worked nicely last night on a 12V supply, then I transferred over to a 12V battery. I'm sure everything was right (polarity etc) but it didn't work, then all the smoke escaped!
Yet to pull the lid off, but I don't have a good feeling since all the smoke got clean away! It won't work without the smoke contained, surely.
Might rebuild it using a circult I understand better. I think the kit I have will fit the box.