Oven Temperature Controller

[GlenG]

I had an old toaster oven that I used when I needed to heat small parts prior to painting, shrink fits etc. It was OK but I was always nervous about temperature control and accuracy, so I recently completed this build. It consists of a PID controller, SSR, thermocouple and various sundry parts. I also stripped out the original oven controls and added 1” ceramic wool insulation to the sides and top as well as reflective foil to the door. The control box is a separate unit so that I can swap out the oven for an other one or for something else that needs thermal control. I’m quite pleased with the finished product.

 

[YYCHM]

PIDs work well for temperature control. I have one for my lead pot.

 

[Doggggboy]

I had an old toaster oven that I used when I needed to heat small parts prior to painting, shrink fits etc. It was OK but I was always nervous about temperature control and accuracy, so I recently completed this build. It consists of a PID controller, SSR, thermocouple and various sundry parts. I also stripped out the original oven controls and added 1” ceramic wool insulation to the sides and top as well as reflective foil to the door. The control box is a separate unit so that I can swap out the oven for an other one or for something else that needs thermal control. I’m quite pleased with the finished product.

View attachment 21141

Excellent.
I have a toaster oven in the shop, (got kicked out of the kitchen by the air fryer) waiting for just such a repurpose.
If I can control the temp well enough it will be used as a rod oven and a filament dryer too.
Care to share the details?

 

[DPittman]

Looks interesting. Should be good.

I think that sort of stuff is what I'd need to add further heat and control to my electric smoker...I need to research if that would be within my limited electrical skills and knowledge.

 

[YYCHM]

Looks interesting. Should be good.

I think that sort of stuff is what I'd need to add further heat and control to my electric smoker...I need to research if that would be within my limited electrical skills and knowledge.

Dead simple once you figure out what the SSR is for.

 

[DPittman]

Dead simple once you figure out what the SSR is for.

Ya but so am I.

 

[GlenG]

Not too much to add in terms of details, almost everything was from Amazon or Wish. There are any number of PID kits that include the PID controller, SSR, thermocouple and the heat sink (make sure you get a heat sink in the kit, I made a mistake and had to but one separately). I picked a PID with a 1300 Degree Range ( a REX-C100), it came with a K Type Probe Sensor and an 40A SSR. I used a combination toggle switch / outlet from Home Depot as my power switch and PID controlled outlet. You see that I used two boxes, but not by choice. I bought one and it as too small, so I bought another it was too small as well (doh). My advice get bigger than you think and then a bit larger again LOL. Wiring is pretty straight forward, run 110v through the toggle, split it to power the PID and the through the SSR to the outlet. Thermocouple to the PID and the low voltage side of the PID to the low voltage side of the SSR. On the oven side, I just took out all the controls and direct wired the elements to the cord. I also installed the thermocouple on the side (you can see it on the right side of the inside of the oven). The insulation was laid in between the oven box and the outer case.

Seems to hold the temperature well, sometimes it will over shoot a bit more then I expected but comes back.

 

[GlenG]

Dead simple once you figure out what the SSR is for.

View attachment 21146

^^This. Dead simple as you can see from the PID connection diagram in the top corner of Craig’s image.

 

[YYCHM]

Not too much to add in terms of details, almost everything was from Amazon or Wish. There are any number of PID kits that include the PID controller, SSR, thermocouple and the heat sink (make sure you get a heat sink in the kit, I made a mistake and had to but one separately). I picked a PID with a 1300 Degree Range ( a REX-C100), it came with a K Type Probe Sensor and an 40A SSR. I used a combination toggle switch / outlet from Home Depot as my power switch and PID controlled outlet. You see that I used two boxes, but not by choice. I bought one and it as too small, so I bought another it was too small as well (doh). My advice get bigger than you think and then a bit larger again LOL. Wiring is pretty straight forward, run 110v through the toggle, split it to power the PID and the through the SSR to the outlet. Thermocouple to the PID and the low voltage side of the PID to the low voltage side of the SSR. On the oven side, I just took out all the controls and direct wired the elements to the cord. I also installed the thermocouple on the side (you can see it on the right side of the inside of the oven). The insulation was laid in between the oven box and the outer case.

Seems to hold the temperature well, sometimes it will over shoot a bit more then I expected but comes back.

Mine has a self calibration/tuning mode that really helps smooth out the temp overshoots. Unfortunately it isn't a saved parameter so I have to reset it every time I use it.

 

[GlenG]

how hot are you able to run this?

Before modified I ran it up to 400, haven’t had a chance to run it up that high since i modified it.

 

[Tom O]

Ya but so am I.

It’s not bad at all and if you get stuck you can always go to this brewing site that shows many ways of making/using them 120 or 220 versions. Another thing is some controls are strictly in Celsius and other are programable.

 

[CalgaryPT]

I had an old toaster oven that I used when I needed to heat small parts prior to painting, shrink fits etc. It was OK but I was always nervous about temperature control and accuracy, so I recently completed this build. It consists of a PID controller, SSR, thermocouple and various sundry parts. I also stripped out the original oven controls and added 1” ceramic wool insulation to the sides and top as well as reflective foil to the door. The control box is a separate unit so that I can swap out the oven for an other one or for something else that needs thermal control. I’m quite pleased with the finished product.

View attachment 21141

Really nice. Pics of the of the control box you built would be nice . I recall learning the math behind PIDs in university and the ahh ha moment around deadbands. Useful stuff to know—most of which I have forgotten now. Good work Glen.

 

[GlenG]

Here are some more pictures of the controller inside and out:

Top Box has PID and input for the Thermocouple:

Bottom box has power in, fuse, SSR, power out and switch (one unit):

 

[Janger]

The SSR is 40A? The toaster oven would draw 15A. Do you need bigger SSR’s? Was there a reason for the bigger ones or 40A was just what was available?

 

[YYCHM]

The SSR is 40A? The toaster oven would draw 15A. Do you need bigger SSR’s? Was there a reason for the bigger ones or 40A was just what was available?

I think 40A is just an industry standard. My kit came with a 40A as well.

 

[Janger]

Good info thank you. What kind of SSR etc would be needed for a 30A 240V kiln? Would the same 40A type work for this much heavier load? Supposing you wanted to turn a regular kiln into a heat treat oven? Used kilns can be pretty cheap.

 

[YYCHM]

Good info thank you. What kind of SSR etc would be needed for a 30A 240V kiln? Would the same 40A type work for this much heavier load? Supposing you wanted to turn a regular kiln into a heat treat oven? Used kilns can be pretty cheap.

Seems to me @Johnwa developed a home grown (Arduino?) temperature controller for the same application or something similar. An off the shelf PID didn't cut it.

 

[GlenG]

The SSR is 40A? The toaster oven would draw 15A. Do you need bigger SSR’s? Was there a reason for the bigger ones or 40A was just what was available?

As others have said they generally come in two flavours the 25 and the 40. I just picked the 40 for over kill and future growth.

 

[CalgaryPT]

An Arduino is sure less expensive than some of the ramping PID controllers. If you can find good code to copy.

There are some good sketches around for the DS18B20 digital temperature probe as well as the older TMP36 analog sensor and an Arduino. Both max out at 125C, but a kludge I've used is to place a piece of aluminium or steel flat bar in a strategic location inside the oven, then attach the temperature probe to the outside of the oven on top of it. Attach a heat shield around the sensor and calibrate it using an accurate temperature gun such as a Fluke. By adjusting the surface area of the flat bar and the material from which it is made of you can dial in the correlation between inside and outside temp, as well as the rate at which it dissipates (which is related to deadband). There is a technical name for this type of system in thermodynamics, but of course I can't think of it now. It's an indirect feedback loop of some type.

The code lets you scale the response according to your needs, so if you are comfortable with writing sketches there is tons of flexibility you can build in, including ramping functions. Adding the LiquidCrystal library to the include code in the sketch gives you a pretty cool display for a really useful project. There is another technique of placing the sensor at the end of an insulated tube and using a small fan running through the oven to push the hot air through the tube to the sensor at the end. This is more accurate, but difficult to retrofit. However, both techniques allow you to utilize the accuracy of the DS18B20 in an environment that would otherwise melt it. It's not perfect, but beats the cost of more expensive sensors specifically designed for higher heat. I read that NASA uses this same technique in some cases, but ups the game by measuring multiple points outside the engine/oven/chamber and using some fancy math modelling to come up with an accurate temperature. So it can't be that kludgy I guess.

If anyone in the Calgary area wants to play with these sensors, I have a couple of the waterproof versions of the DS18B20's laying around.

I actually made an overly complicated version of one of these for a PTZ CCTV camera once that turned on a heater when the camera's case got too cold. It was overkill by a factor of 1000, and had no practical application on the scale I built it. But it was a challenge and learning experience for me that mixed metal fabrication, electronics, CCTV, programming and math.

(It probably goes without saying that I had no girlfriend in high school though.)