I have seen a few version of how others have made these, and went for the one which looked the easiest and cheapest to build,
I started with a 12 volt PID controller, which can be purchased from a certain auction website. All I needed then was a 12 volt computer cooling fan and a box to put it all in. The box is connected to the UDS with a short piece of 28mm copper pipe, and attached to the UDS with 28mm-3/4" male iron connectors and back nuts.
The PID is set to run at a certain temperature, and trained to maintain and smooth out the up and down temperature effect. It does this with clever calculus, that is able to predict when the heat is needed, and when to stop the fan to maintain an even temperature.
So, having put all this together, it was time to try it out. On advice from another member, I ran the UDS up to temperature, and then "trained" the controller, using a function called auto-tune. This is where it monitors the variations in temperature, and begins to predict the need for heat, switching on the fan as needed.
And it works fantastically, keeping the temp to within five degree's either side of the set temp. It's been running since 3 O'clock and it's now nearly half past eight.
I'll post pics tomorrow, so you can see what I have been prattling on about.
Iam going to put a piece of Gammon in as well, to see how it fairs with food in it.
Edited by Baz Senior - 11/24/13 at 6:41am