I may be re-inventing the wheel so please humour me if this has been done before.
OK here it is... the big secret, a 400g baked bean can
Basically it's a micro incinerator that converts wood chips to charcoal and then smoulders the charcoal. Getting the air flow right was the tricky bit! Take the top off and enjoy the contents. In the base drill twelve 8mm holes, I did 3 in the midddle and a ring of 9 around the outside. On the sides just above the base drill eight 8mm holes. 2cm higher drill eight more 8ml holes, staggered to the first set. 2cm higher drill ten 6mm holes. 2cm higher drill twelve 4mm holes and finally 2cm higher drill fifteen 3 mm holes. fill loosely with wood chips and ignite with a cooks blow torch. There is an initial burn that converts all the chips to charcoal and would be more suited to hotsmoking than cold. Once all the chips turn to charcoal the flames go out and it starts smouldering, once it has burnt down to an inch or so just top up with wood chips again, these will convert to charcoal without flames so it is now self sustaining, just keep topping it up. Ash and the occasional bit of hot charcoal falls out of the bottom so you need to stand it on a rack, it worked fine in a kettle bbq when I tried it last night, but the bigger the box and the better the air flow the less danger of heat build up.
Good luck, I'm sure it can be improved on but I thought I'd share the Mk 1 with you
Dave