Thanks everyone for the suggestions. Today it reached 38°C in the shade, maybe that had something to do with the overheating.

We may try and bash some old heatsinks we have around the place into circles and make our own. Thanks for the link, though.

Dave, thought so! Sadly we'd need 2, putting the 'extra' at a £52, some £52 over budget!

I'll be contacting the guy(s) behind BotBitz as to whether they think their 25a models would be happy working around their limit. We have blown a 15a fuse with a single normal 12v drill in the past, so on paper they'd be right on their limit. If they say they'll be fine, then we'll probably go for them.

Thanks.