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How to transform your old electric oven into a modern digital thermostat controlled one (aka: the meringues solution!)

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Picture of how to transform your old electric oven into a modern digital thermostat controlled one (aka: the meringues solution!)
If you ever tried to cook meringues you knot that it's almost impossible if your oven can't keep a constant temperature over the time. Modern electric ovens have a digital integrated thermostat so to achieve that goal with no efforts, but if you like meringues and you have an old oven you could probably feel in troubles.. old thermostats only have a graduated scale, and the only way to maintain the exact temperature is to put a thermometer into the oven, then set the knob consequentially.
A better solution is to buy a digital temperature controller with a thermocouple, and connect it so it will regulate the oven in place of you.

NB: this PID controller support 250V at 3A, it means 750 watt. For any oven more powerful than that value an external 5A relay is needed.
 
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Step 2: The connections

thermo07.jpg
Here you can see the diagram of the connections to the back side of the controller. This model works with AC 100-240V, but you can find controllers powered with different voltages. You have to screw the power cables to pins 1 and 2. One of these same cables has to be connected with one of the relay pins (I used the number 3). One of the remain relay pins has to be connected with the female socket. The pin 5 is NC (normally closed) and the 4 is NO (normally open), connect to pin 4 so you'll need to change no parameters in regulator settings.
Connect the K type thermocouple to the 9 and 10 pins, paying attention to the positive and ground wires.
We don't use the "alarm" funtion in this project.
verence9 months ago
Cool. An industrial controller on a household appliance - I like that.
andrea biffi (author)  verence9 months ago
thanks verence, this could indeed easily adapted to other appliances, as a fan or an air conditioning system (although it probably already has something similar), and of course the little ovens to warm up the bread in the morning, which usually lack of the thermostat
I didn't know that you can get PID controllers that cheap. The ones I used for work (years ago) did cost hundreds of dollars. My oven has a working thermostat but just with a knob to set the temperature and without any display. For this cheap price, I'm tempted to do it just for the nerd factor.
andrea biffi (author)  verence5 months ago
Container is done! I'll publish the instructable tomorrow
andrea biffi (author)  verence9 months ago
I believe you, that's the reason which pushed me to modify my oven (more than the love for meringues!). Now I'm working on the container for the controller and the socket.
JasonInBoston9 months ago
This would be a great solution to using the oven to raise dough!
I never understood why my oven manufacturer would have the lowest setting of a high-end digital oven be 160F. I've always wished I could set it someplace between 80F and 110F to let bread dough rise at a controlled temp.

Thanks!
andrea biffi (author)  JasonInBoston5 months ago
Yes, it works great, and it's also a very cheap solution. I'm writing a new instructable about the new plexiglas case.
waldy9 months ago
No work, like my meringues, must try this soon
weburn29 months ago
Great idea, but I don't know what a "grate" is that you have the thermocouple attached to. Should it be in the oven somewhere?
andrea biffi (author)  weburn29 months ago
I mean the metal grill inside the oven, as in the last photo..
Monty^9 months ago
I've been wanting a controller for my thermoelectric cooler and it's nice to learn there is a low cost alternative.
flobster9 months ago
I could not download the instruction manual from the link provided, but I am quite sure that the build in relay in the PID is only rated to switch a couple of amps. That is not enough for an oven. I would use a separate relay and let the build in relay switch that.
andrea biffi (author)  flobster9 months ago
you're right, I should had specified it in the ible, this PID controller support 250V at 3A, it means 750 watt. For any oven more powerful than that value an external 5A relay is needed. I'll update the instructable, thanks!
altecom9 months ago
A step further could include the controller to switch on and off only tehe resistors , some ovens have a small fan that can be kept working to uniform temperature inside the oven.
We ourselves use brands as Fuji PXR3 , a 1/32DIN controller , half the size that can eve perform temperature patterns as heat to 50º in 3 mins, hold the temperature and rise again to another value and even to "cool" down in a precise program.Try it , you'll be amazed the way these gadgets work.
altecom9 months ago
Very interesting, years ago ,we did something like that , but for our truck's a/c , worked beautiful , mantained the temperature in the cabin plus-minus 1ºC.
lindarose929 months ago
You must take pictures of the meringues YOU made using this thermostat to prove that it works... :P
andrea biffi (author)  lindarose929 months ago
mmm for now I'm on diet ;-)
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