It's a home made 'charger', basically just a chunky transformer, 25A bridge rectifier and capacitor capable of supplying 10A and more. The ammeter is a 10A moving coil type.
Noted re fan, it still sounds as loud as it always has done so I think is's OK. It cooled the box down to -1 yesterday while I was testing it, that's 15 deg below ambient.
The wire is still contained in the glass fuse, but for sanity's sake I'll see how quickly a single strand melts in a short circuit situation.