Hacking an induction burner

I’ve been homebrewing beer for 20+ years, all on my stovetop. I’d like to be more precise about it, so I was thinking of hacking an induction burner to use for a mash tun - this requires holding the temperature at a steady point for fixed periods of time, and depending on how complex you want to get, ramping the temps up and down at fixed intervals. Seems like an ideal project for an arduino, and there are even a handful of arduino and pi based setups out there that address certain aspects of this.

What I’d like to do is replace the control circuitry on a cheap 1800W induction burner. Looking at how these work, it seems like a fairly simple process: remove the existing circuit and replace it with relays as necessary to turn on and off the induction element. A thermocouple would be used to monitor temps, and the arduino would fire up and turn off the heat as necessary.

My question is: is there an induction burner anyone can recommend that’s easy to hack? That is, something that’s physically easy to work with, and that has enough room inside to fit an Arduino Uno (though I could go smaller if necessary), and the necessary relay(s)? I’d like to keep it neat, so that everything is self contained inside the burner’s existing enclosure.

One other possibility is putting everything in an external enclosure. The induction burner gets hardwired to go on any time the power is plugged in (bypassing its control circuits), and my external box just turns the power on/off. It would have an outlet built in, and the induction burner would be plugged into that.

Thanks!

-perry

Do you really just want to turn the burner off and on? Wouldn't it be better to be able to control the voltage/current to the heater?

I fear that you are on your own with the heater selection. In detail the EM field of the inductive heater will disallow to put any other circuitry below or into the same enclosure, IMO, so that an detached controller will be the most practical solution.

PaulS: Do you really just want to turn the burner off and on? Wouldn't it be better to be able to control the voltage/current to the heater?

I don't know much about how induction heaters work - would it make a diference, if I'm just pulsing the voltage on and off in a pattern that brings it up to temp? We're talking about a couple gallons of liquid in the pot, so quick bursts of higher temp shouldn't scorch anything.

If the way to do it is to control the voltage, then I suppose I could look at how the burner I get is doing it, and try to just replace the controller in it with my Arduino to do the same thing. Then I wouldn't be replacing any relays or anything.

DrDiettrich: I fear that you are on your own with the heater selection. In detail the EM field of the inductive heater will disallow to put any other circuitry below or into the same enclosure, IMO, so that an detached controller will be the most practical solution.

Looking at images of the inside of these things, it seems like most have a simple microcrontroller on a single board inside the enclosure. Why would replacing that with an Arduino be any different?

I've attempted something similar. If you don't have a lot of experience with hacking high-power circuits, I suggest what you do is this - instead of hacking the power board, open up the board which controls the display. Locate the buttons which, when pressed, determine whether power should go high or low.

Then, use optocouplers (4N35 works nicely, though any other cheap model should work equally well) to pulse-open the switches to raise the power supplied, or lower the power supplied. Connect these to your Uno, or whatever you choose to use, and keep a track of your power output at any moment in the Arduino code.

Most cheap induction cooktops are Chinese-make models with circuitry whose datasheets are not very easy to find (I've spent weeks on this!). So this optocoupler business is a good, cheap workaround, and you don't have to bother with the exotic ICs they put in there.

This post might be of some help: http://www.instructables.com/community/Is-it-possible-to-link-Arduino-modules-with-a-port/

And this post would also be helpful : http://openschemes.com/2011/04/28/manual-control-of-the-1-8kw-induction-cooktop/

All the best!

Also, replacing the display board completely with an Arduino is ideal, but I suspect it becomes a project on its own. If you can figure out the I2C communication protocol between the display board IC and the power board IC, then you’re golden. I tried a bit, couldn’t figure it out, so satisfied myself with :

Uno → Display board IC → Power board IC

And as DrDiettrich points out, if you’re a beginner, best to start with the Uno in a separate housing, and attempt replacing the display board/merging the housing in subsequent iterations.

Thanks. I'll look into the optocoupler route. I bought a cheap one on Amazon yesterday so we'll see what happens when it arrives. From what I've read, only the commercial models can be relied upon for precise temperature settings, but the plan is to first test the unit I get and see how accurate it is. If I can make it work without modification, it may be good enough. But if I do need to tweak it, I think your suggestion makes sense. I've done a bunch with relay control of AC line voltage in my film scanner, and I did a lot of the AC wiring in my house (under the supervision of an electrician, who double checked everything - saved me a bundle), so I'm reasonably comfortable and very cautious around it. I'm not worried about that at all. I'm mostly not interested in this becoming a massive undertaking, because I've got a lot of other stuff going on, so replacing those switches may be all I need to do.

Thanks!

Heaters rarely use voltage control. They use a "simmerstat" or very coarse "PWM" or "duty cycle" control as they take seconds to change temperature significantly.

Induction heaters may have less thermal mass, so may need to operate faster, but generally you arrange the SSR to switch on for a number of full cycles of power and off for a number of full cycles, either over several seconds or perhaps a 2 second cycle time.

Don't forget that you need to use magnetic stainless steel (or iron, or copper) with an induction cooktop.