Convert kiln/oven to digital control

[dbb-the-bruce]

I have a smallish (bench top) muffle oven that runs on an analog duty cycle control. I'd very much like to convert it to a modern digital controller with temp feed back etc. Not looking for anything overly complicated. Seems like it should be a pretty easy conversion IF I can find the right drop in control and sensor. Just need to make sure it handles the current draw of the heating elements installed.

I did some searching but didn't really find anything that made me feel confident I could just buy and wire up. Probably I'm not looking for the right thing. Any experiences / suggestions or pointers would be greatly appreciated.

Thanks.

 

[markba633csi]

All you need is a solid state relay (SSR), a temperature controller and a thermocouple sensor. There are several types of thermocouple for different temperature ranges, the most common is K type, it measures to over 2400 deg. F
The SSR should be rated for the voltage and current of your kiln
Look on Ebay, Amazon or Aliexpress you'll find complete packages
-Mark
PS Here is an example of a long-reach thermocouple for kiln use:

6.84US $ 43% OFF|High Temperature K Type S Type Thermocouple Sensor For Ceramic Kiln Furnace 2372 Fahrenheit 1300 Degree Wrp-100 Thermocouple - Thermometer Hygrometer - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

 

[Gaffer]

I bought a large old kiln on the cheap a while back to convert to a heat treating, etc. oven. I recently bought the following and other goodies for the project, like switches and an electrical box to install the components into. I wanted ramp and soak, but there are cheaper PID's if you don't need those features.

Amazon.com

Amazon.com

Amazon.com

 

[benmychree]

Current load won't matter if you use a relay contactor to carry the main load. Ramp up is not necessary for anything that we are likely to do.

 

[B2]

SSR-30DA or SSR-40DA, a thermal couple and some electronics. The on off cycle on an oven is long times so speed is not an issue. Yes, you could use some big mechanical relays/contactors as well, but will require a little more in the way of the control power/electronics. There are lots of simple control modules on the market that take a thermal couple as an input. Google search with terms like: Digital+PID+Temperature+Controller+with+SSR+and+High+Temperature+Probe
If you do not have High in there you are going to get a lot of room temperature controllers.

Here is a google example but you can probably do something similar on Amazon etc.

Digital PID Temperature Controller with SSR and High Temperature Probe (2280 , 2 Alarms) - Google Shopping

www.google.com

I do not know what the current draw is for your unit, but I have used these Fotek SSR devices to switch 220V. There is a 30Amp and a 40Amp version. I used the 30Amp version. I used these SSR to power several things... and they are cheap (~$15). Some even come with a heat sink, but you can usually just attach it to a case, but if you are going to push the amperage then you may want a good heat sink. Also, use some thermal paste. They switch off and on via DC at a few milliamps (3-28VDC). I got turned on to these when I remodeled the kitchen and I put them in to control the garbage disposals. I installed a magnetic sensor below the counter top and moving a vase on the countertop, which contains a magnet, over the sensor causes the disposal to run. (no holes in the counter top or sink for a vacuum line. The simple control electronics run off 4 AA batteries and the magnetic switch to turn on the 220VAC. No battery power is drawn except when activated by the magnetic field. That was ten years ago. I just recently had to change a battery as one of them corroded. The other 3 were still good at 1.5 volts. So it did not consume the battery power, the battery just leaked! The electronics are in the cabinet under the sink and there I put a redundant traditional three position switch to either turn the disposal on mechanically, turn everything off mechanically, or to turn on the magnetic sensor system.

It worked so well I built three of these things.

Good luck.

 

[homebrewed]

I'm curious if any of those upgrades required tuning of the controller (the P, I, and D values) to get stable & accurate temperature control. Decent controllers have the option of changing them to suit a particular application. Really fancy ones have auto-tuning.

Out of the box, the controllers _probably_ are set up to produce decent results for a wide variety of situations, but the performance may not be all that great -- it may take longer than necessary to get to the set point, the temperature swings may be pretty wide, etc. But maybe not an issue for a hobbyist.

 

[B2]

Yes, better controllers do all sorts of fancy things such as different temperatures for different periods of multiple times, temperature ramp rates, dwell times at one temperature prior to going on up or down (i.e. temperature profiles), anticipate temperature so as to not over shoot on either heating or cooling, etc. I used to have expensive controllers for my labs, which would do these things, but today you can do almost any of these "features" with simple microcomputers ... so why should the cheaper ones not have these sorts of features today. But yes, sometimes, "features" make things harder to understand ... or to get them to work ... or in some cases more likely to fail. All depends upon on what you want to achieve and how fast you want to get it to working.

 

[dbb-the-bruce]

Lost of good comments. This discussion has clarified a few things.

First and foremost I'm looking to hit and maintain a given set point. Anything else is gravy and not likely to be used much, however any decent modern controller should be able to ramp and I can conceive of using that for cooling down sometimes rather than just shutting the oven off and letting it cool naturally.

I've been using the oven to enamel in addition to heat treating and I'd really like a control that can quickly accommodate and recover temperature drops when the door is opened.

I checked the power plate and it claims 10 amps @ 110 V, so not particularly big or scary to try to control. Should be something readily available.

There were a couple of comments about having to tweak or tune the PID to get good response. I've done plenty of that in past for mechanical systems and would really prefer something that's either smart enough to figure it out or already pretty well tuned.

I'm not looking to spend a fortune on a top of the line do-it-all controller, but I'm also at a point in my life where I'd rather spend a few bucks than spend a lot of time. Something that's basically plug and play.

I'll check out the links.
Thanks.

 

[Karl_T]

I just want to follow your progress. My very old heat treat oven needs this upgrade. Thanks for paving the way.

 

[dbb-the-bruce]

I'm probably going with this controller and will get the rest of the stuff from the same company.

Controler

I just spent about an hour looking at what they offer - nice to have a one stop shop for controller, thermocouple, box and switches. I don't need (and most of us probably don't either) the ramp/soak capability but the controller has a built in SSR (solid state relay) that can handle my small 110V / 10A oven.

Could possibly save a few bucks splitting the order up or going with a simple controller, but would then need to also buy a relay and mount / wire more stuff.

I'll post follow on when I pull the trigger.