controlling a mains-powered oven

[Jim Nagel]

Has anybody used a Pi to control a mains-powered device? I'm looking for some tips.

The electronic controller of our electric double oven is no longer reliable -- temperature varies far too much, according to the independent external thermometer I bought. Rather than spend £200 to replace the controller, I fancy using a Pi instead. It could live inside a nearby cupboard door, with a nice big screen at eye level instead of the present little thing for which I have to don specs.

Seems to me the Pi's job would basically be to read a temperature sensor in each oven (smaller upper one and larger lower one) and trigger relays (or nowadays maybe thyristors?) to switch various heating elements on and off accordingly. (That's top and bottom element in each oven plus a fan element in bottom oven.)

Would this be feasible? Anybody done it already?

[David]

Thought this would be very appropriate to uk.d-i-y

[The Natural Philosopher]

It was, 6 months ago...

[spuorgelgoog]

Are the Usenet tapes being sent by tramp steamer these days?

Owain

[David]

The thread has been updated more recently with further comments and a success story.

Which is why I saw it near the top of current (umm...no pun intended..) posts.

Fettling ovens for fine temperature control seemed very appropriate to a DIY NG.

[tabbypurr]

A bimetal stat surely makes more sense

NT

[newshound]

A bit crude. I would just use one or two of these

[Chris Hogg]

That's extraordinarily cheap for a PID controller (assuming it works reliably!). The problem with temperature control in any closed container (oven, pottery kiln, whatever) below several hundred °C is that heat transfer is largely convective, and the temperature control achieved is very dependent on where the sensor is placed. A more even heat distribution is achieved in a fan oven, which of course is why they're made.

[Theo]

I've got one of those. For 11 quid including controller, thermocouple, solid state relay and (clumsy) heatsink it's pretty good value and works reasonably well. The UI is a bit odd: there are lots of variations and mine doesn't quite operate in the same modes as others - even in the supplied instructions (entirely in Chinese) are wrong.

The thermocouple is a bit off cal but I think that can be adjusted. I haven't hooked it up to the oven, but a brief test with a soldering iron seems to work fine. I can calibrate it with another controller when I've packaged it up.

Indeed. The trick is to have a lightweight thermocouple (ie just the welded wires, not a big metal lump like the one they supplied) and insert it wherever you need the temperature applying to. Then you have the accurate temperature of the thing you want, and it doesn't matter what the temperature is elsewhere. Unless you have some object with strongly differing thermal properties, that is: you might cook the middle of the cake but burn the outside.

You can still apply the same technique to a fan oven, of course, just the heating curve will be different.

Theo