Welcome back, folks.
You may have read our first two articles on investigating and analyzing a low-cost induction cooker, but if not – check ‘em out!
1800W Induction Cooktop Teardown and
Circuit Analysis of the 1.8kW Induction Hotplate
And you’ll see that we’ve left it kind of open. Promising more, but never delivering – oh, snap! Well it took some ego-boosting and a genuine request from Mark in the comments of the last article, but we are now sufficiently shamed to go ahead and spill the beans.
This device is remarkably easy to control manually.
As we were testing different methods, we did a dumb thing and left a wire connected to the comparator right next to the power switches. Needless to say, the wire drooped over accidentally and touched the heatsink (which is also electrically “hot”, BTW) and 1200V blew out the majority of the important silicon on the power board. Doh! So while we wait for our replacement device we’d be glad to share what we know. We believe that it’s enough to get you up and running with manual control, but since the “striking” technique has only been tested in sim and not on the bench, please consider it beta and subject to change.
You need three things to get this board running under manual control.
- To apply +5V to the “K” line in order to enable the device.
- To apply an adjustable voltage (about 0-3V) to the PWM line to control the power output.
- To strike the device into oscillation using the PAN line.
So let’s take a step back and show you this dangerous piece of pwnership from start to finish. All the control can be achieved through the ribbon cable – no splicing into the circuitry is needed! In our case, we just chopped the ribbon cable off at the controller board, and threw the controller board away. You may want to build a nice professional board, so consider this before chopping anything up. Let’s investigate the ribbon cable and it’s functions, starting at the pinout. Here’s a pic of the discarded control board to help us define the pinout. Pin #1 will be “I-AD”, the pin closest to the 7-segment LED display. Pin 12 will be the one closest to the edge of the board.
Fig 1 – Control Board with Ribbon Cable Removed
The pinout, and functional description is as follows:
- I-AD. Voltage output (for an ADC) corresponding to the average current from the AC line
- V-AD. Voltage output corresponding to the AC input voltage
- GND. The Low-voltage ground to run the control circuitry. WE USE THIS.
- +5V. 5 Volt supply for the control circuitry. WE USE THIS.
- INT. Square wave output of the first comparator. Tells the micro the duty cycle. We don’t use it
- PWM. Power control line. Usually takes a PWM from the micro, but we will drive with a DC voltage. WE USE THIS.
- PAN. Used to strike the switching. WE USE THIS.
- K. ON/OFF control. WE USE THIS.
- FAN. Fan control. Probably should use it, but don’t right now.
- BUZ. Buzzer? Not used.
- T_IGBT. A thermistor tied to the IGBT’s for overtemp monitoring. Currently unused.
- T_PAN. Another (optional) thermistor near the pan for overtemp monitoring. Currently unused.
Now here’s your 2-minute overview of manual control for this device.
- Tie K to +5V to enable the device, or to a switch for on/off control.
- Apply an analog voltage (about 0-3V) to the PWM line to adjust the power. We use a potentiometer.
- Strike the device by pulling the PAN line high momentarily.
Simple, eh? So what’s all this “striking” business we keep talking about? Well basically, since the system is self-oscillating, it uses the ringing on SW to decide when to start a new cycle. If SW is not oscillating, it’s happy to just stay still. In order to get the system running, we must disturb it using the PAN line and force it to start a cycle. After that first cycle, the resonant ringing on SW will allow it to self oscillate and Bob’s your uncle – you’ve got an induction heater!
So let’s do it. Please double, and triple check that the AC cord is disconnected and the capacitors have had time to drain before playing around in the circuitry. We’re assuming that you’ve already cut the ribbon cable and identified the 5 lines you’ll need (GND, +5V, PWM, PAN, K).
For simplicity, let’s just tie K to +5V for now. That will enable the device any time the AC line is plugged in. Good enough for our needs.
To adjust the power level, you can use a 10k potentiometer between +5V and GND whose center tap (the adjustable node) is tied to PWM. The working range on PWM is about 0.5V minimum to 3v maximum. If you go too low, the device will lose self-oscillation and you’ll have to restrike. If you go too high, then the cycles will self-terminate at about the level they would at 3v. You may also lose oscillation. So keep it around 1/3 to 2/3 and you should be able to sweep the power level from a few hundred watts to the full 1.8kW. We’ve gotten away with pots as high as 100k, but internally there is a 200k resistor to GND which will end up acting as a voltage divider to limit your maximum V(PWM). That might be a feature to prevent over-revving, actually!
The strike requires a momentary pushbutton switch, connected from +5V to the PAN line. When you tap this switch, it whacks the TOPREF and SWREF nodes in such a way as to force the first comparator ON, which tricks the device into starting a cycle. There is already a 22k pulldown resistor from PAN to GND, so it doesn’t matter if you push and hold the strike button or just tap it, it will decay back to 0V pretty quick so all that is needed is a pullup. It’s the sharp rising edge of PAN that does the deed, so a momentary pushbutton switch is the perfect thing to do this.
The timing is not critical – that ugly startup noise we described in the first article is the micro banging this line tens of thousands of times in a row. So for you – it’s probably OK to tap it a couple of times, but you don’t want to sit there whacking on it for too long – you are forcing a cycle every time you tap the switch and the switches don’t want to be forced on when the SW node is at it’s 1200V resonant peak. We’ve never killed any switches with our manual striking, but we can tell you that repeating striking while the device is running is simply not a nice thing to do to your induction heater.
So there you have it: Enable, set power level, and strike. Easy as pie.
It’s certainly possible to unwind the pancake coil and rewind it around a piece of PVC or something in order to get a cylindrical coil for heating rods, etc. Keep in mind that the lacquer used may chip off and give some risk of breaking the insulation. Exposed coil wiring is something you definitely would not want to touch with either your hand, or the piece of metal you are heating.
More details are just around the corner when the new unit arrives – stay tuned, and good luck!
By zdw April 29, 2011 - 7:30 am
Any idea if this thing could be modified to degauss a hard disk?
I’m wondering as the degaussing plates made for hard disks are quite expensive, and superficially appear to be similar in functionality to an induction cooktop.
By openschemes April 29, 2011 - 4:27 pm
Probably not, but you could try it. Perhaps at low power levels it could erase a disk, but at high power it would probably just cook it. You would also have issues with the outer plates (or even the shell of the drive) acting as a magnetic shield and sucking up all the flux. The outside would cook, but the inside may not be affected at all.
By Asmodyne June 8, 2011 - 6:48 pm
Great bit of hacking you did there lads !
May I ask if you tried different coils configurations on this baby ?
Because as I see it, this hotplate design isn’t fit for metal tampering/melting under a frequency this low (Foucault currents would dominate over the skin effect at such a low frequency, am I right ?).
So I wondered if the coil intensity feedback signal was used in some kind of protection mechanism in the original design. Cuz having too small a work inductor (say 5 to 10µH) would cause higher intensity spikes, wouldn’t it ?
Messy question made simple : What is the highest frequency you obtained out of this nice setup ?
By openschemes June 9, 2011 - 4:39 pm
We have used a 45uH cylindrical coil to heat rods. In the original application, the micro probably checks the frequency and shuts it down if it’s too high. As you may recall, the cooktop won’t run without a pot or some other significant load.
The highest frequency was about 75kHz. The problem is that without a strong gate drive, your SW flies up before the IGBT is fully off. This will end up cooking and killing your IGBT’s when attempting to run at a higher frequency. We’ve duplicated the cooker circuit on our own PCB and found exactly this problem. And as soon as we finish the Xyron hack, we plan to work up another PCB with a real mosfet driver running the switches.
That one will be limited only by the storage time of the IGBT’s, which is still significant. So could you possibly run it at 200kHz? Probably, but 1MHz would never work without MOSFETs.
However, industrial metal melting does not use high frequencies – more like 10kHz to get some actual penetration into the work. It’s only surface treating and nonmagnetic stuff that needs higher frequencies.
By Asmodyne June 9, 2011 - 8:08 pm
Thank you for dissipating the fog in this hazy brain of mine. Skin effect…surface tampering…makes sense here.
Tweaking the original circuit by using mosfet would be great (I endorse it, thumbs up), but is there any reference which could withstand such current and voltage ?
As I read it, the here used IGBTs are rated 20A (60A peak) @ 1.2KV. It will be difficult to find mosfets rated more than 18A under 800V with the same package. We’ll soon hit the SOT-227 family and such modules.
The affordable STW20N95K5 can endure 15.5A (62A peak) @ 950V with a huge heatsink, but that’s it.
Don’t you fear the project can quicky turn into a bottomless pit ?
Man, oh man, I’m thrilled about your next experiment.
This article is a real cliffhanger.
By openschemes June 10, 2011 - 5:19 pm
Yup, finding a FET that will drive that much power may be impossible or at least impractical – as you mentioned, bottomless pit.
The beauty of this design is it’s simplicity, and ease of low-side driving. The drawbacks are seeing the huge ringing voltage on the switching device, necessitating something like an IGBT to take the abuse. To get increased power and increased frequency while keeping your voltage ratings low, you’re going to want to go to a half bridge configuration. Uzzors2k, Tim Williams, and others have build extremely powerful devices that can use MOSFETS due to the fact that the switches only see one VIN’s worth of voltage. Still 200-300V, but it ain’t 1200V! The drawback of those is that the high side drive is not trivial.
We may try one of those alternate topologies in the future, but the goal of a 30kHz, 1.5kW device seems reasonable for this one here.
By Mark O'Hara October 13, 2011 - 8:06 am
Is there any progress on this. Did you get a chance to obtain another device? Also, what would be the simplest means of getting more power at 10 – 20 kHz?
Thank You
Mark
By openschemes October 13, 2011 - 4:45 pm
Funny story – another device was purchased a long time ago but was delivered somewhere else. Never found out where. It was such a pain to get the money back that no second replacement was ever purchased. But that should be corrected – the replacement will be purchased tonight.
Some calculations would need to be done to figure out the total max power that this topology could do. Probably the limiting item when using a modified stove is the power switch current, so in that case more switches could simply be added in parallel. Second limit would be the 15A breaker on a typical household plug, you’d want 20A or 30A and then an upgrade to the bridge rectifier would be required. Next, the tank and resonant caps would need to be upgraded and finally, switch to 240V to obtain even more input power.
Why, what’cha trying to melt?
By Jason January 29, 2012 - 1:22 pm
Great article! I’m looking into driving my hotplate with a PID to create a hotplate for a water bath that will be able to hold a “constant” temp… I have an Aroma Induction cooktop that I got at Costco for $49, and really want to give it a try… I have a little electronics knowledge, arduino, some temp control & PID, and a little programming but usually stay away from AC, especially 2500V!
How hard would it be to hack my induction cooktop to just turn on high if there is AC power and a capable pot was on the burner??
Sounds like I need 5v and 3v, I’m still trying to figure out this Strike thing… It’s outside my normal knowledge set!
Great post and I will check back to see how it progresses after your replacement burner is in.
-Jason
By openschemes January 29, 2012 - 9:49 pm
Hmmm.. $49 at Costco, eh? Sounds like something we should pick up.
The burton can already hold at a constant temp. Are you saying that yours cannot? To venture a guess, adding PID would probably be a matter of reading a thermocouple or thermistor with your micro, and outputting a PWM signal that you RC filter to a DC voltage in order to control the cooker. The replacement burton cooker is in, but has not been hacked due to an overwhelming pile of other projects. We will kick some stuff off the top and see if it floats up to a higher priority for ya..
By Scott February 7, 2012 - 11:13 am
In case you need extra Max Burton units to play with ($50, shipped) : http://www.toolup.com/max-burton_6000_induction-cooktop-by-max-burton-6000-series.aspx?&utm_source=CAfroogle&utm_medium=CA&CAWELAID=631497450
I’m really hoping you pick this project back up. I’d really love to hack a Auber PID temp. controller into the unit for more precise temp control, but I don’t quite have the know how to pull it all together … basically just enough knowledge to be dangerous (mostly to myself). Ideas?
By Paul May 27, 2012 - 9:32 am
This series of articles on the induction stove top have been amazing. I took apart my non-Max Burton unit recently and was pleased to find that it was very similar to the unit you documented. It turned out to be a Better China product like yours, just a different model. Fortunately there were enough similarities that I could adapt your work without too much effort. Mine is sensitive to a slightly different range of input voltages and the PAN line needs to be pulled to ground, not high, among other various component choices/values.
After verifying the critical things hadn’t changed too much and compensating for various changes in components, I have a potentiometer-controlled 1.8kW induction top! I ended up bypassing the microcontroller entirely and have a separate switch to control the cooling fan. I leave it on whenever I have it powered on, just to be safe.
Anyway, I want to thank you for your pioneering work. Without it, I don’t think it would have been possible. My goal is to get a nice stovetop for sous vide cooking in addition to just getting more precise temperature control of the stovetop. My next steps are to figure out the full range of voltages I can apply before losing oscillation to see if I can get sous vide appropriate temperatures simply lowering the power in the coils. It is possible that those low powers will cause a loss of oscillation in the circuit, requiring me to put a microcontroller in the loop to restrike the circuit. Otherwise, I have a Watlow self-tuning PID unit which should be able to control the circuit without too much trouble.
I’m not sure if you will read this as this post is a little old now, but I had great success with my unit, thanks in large part to your work and effort. Thanks so much! I am thinking about getting a bunch of units for friends and family and modding them for their use, if they are interested. It works way better than electric stove tops, and now it is much better than my gas stove, too.
By openschemes May 28, 2012 - 8:59 pm
Congratulations! That’s really great work, it’s awesome to hear you got it up and running. Which model did you use? Others would surely be interested in hearing about your hack!
If the power level you want for sous vide is lower than a reasonable setpoint for the oscillation, you may consider wasting more power. Seriously, though! Try a large chafing dish with no cover or a partial cover – by losing more watts of heat to the outside world, the induction heater will need to apply more watts to the dish in order to keep even a moderate temperature such as is used in sous vide. Then, the power setpoint may end up being a more convenient level and avoid the risk of losing oscillation.
Your use of this hack is a very cool one. If you ever consider doing a writeup and taking a couple of pictures, we’d he happy to host it with your credits – just let us know! Email us at IH@ .. this site… or admin@ …. if you would like to.
By Paul July 9, 2012 - 12:27 pm
I am using a Magneflux induction stovetop. It’s a single burner 1800W unit that my mother-in-law got me from Tuesday Morning. Everything was going well: I had my Arduino set up with a 5-button interface, a thermocouple with cold-side compensating thermocouple amplifier, a RC filter to handle the PWM output, and an 2×16 LCD for system feedback and the rudimentary GUI.
But, alas, last night my stove suffered the same fate as yours. I had a dangling wire connected to ground on my microcontroller side that touched the (metal) case of my induction stove. Apparently it was electrically hot. I haven’t figured out if that is how it was constructed or if a wire or contact touched the case when I reassembled it with the wires going out to the external microcontroller. Anyway, it nearly welded the culprit wire to the metal case. After the smoke cleared, I looked inside and only really saw the 7805 regulator blown as well as a few traces leading to the 7805. Also, the regulator on the Arduino seems to be busted. If that is all that is busted, it should be an easy if ugly fix. I will hopefully have know more by the end of the week.
Regarding the power for sous vide, it’s never been a problem for me to dissipate extra power. I was going to take a similar approach to what you suggested, just using big metal All-Clad stock pot with an open top. It will dissipate lots of heat, but will also have a large thermal mass to make temperature regulation easier.
I have some images of the pot-driven iteration, but I will maybe take some higher quality shots of my setup and pass them along. I might wait until I get it fixed again… Thanks for the offer!
By Bodo Heiss June 20, 2012 - 4:01 am
I am also planning to use a PID to control the induction heater. For that I plan to use the osPID.com device which has been derived from an arduino.
Though I have been able to identify same-built models to the Burton tabletop it would be nice to get more information on:
- your variant of the “Better China” induction heater and about
- how you are managing the high current of your directly PID switched design
By Bodo Heiss August 1, 2012 - 8:09 am
I have (what I thought) found an identical device (220 Volts brand: Alaska IC 1800 W) which however is a streamlined version.
Instead of 12 connections between the control and the induction board it only features 7. The PIN outlines are also missing, so that I cannot easily indentify the relevant pins. Can someone help me ?
https://rapidshare.com/files/1797208092/control%20board%20front%20and%20back%20flipped%20alaska%20ic1800w.jpg
https://rapidshare.com/files/1184981358/induction%20board%20front%20and%20back%20flipped%20alaska%20%20ic1800w.jpg
Best Regards Bodo
By openschemes August 1, 2012 - 7:41 pm
Nice pics! Instead of the control board, you will get more information from looking where these signals go on the main board. 5V and GND should be easy to figure out – use a multimeter if tracing the lines is just too difficult. But if the pins are not labelled, you’ll be interested in any signals that travel over to the LM339 comparator chip that should be on the mainboard as well. Do you see that chip?
By Bodo Heiss August 6, 2012 - 8:45 am
Sorry for the late replay and thanks for your remarks and compliments.
I can only find one 14 pin chip (which is the pin out of the LM339) on the main board; thus this has to be the one.
I have marked the chip with an arrow:
https://rapidshare.com/files/4106604866/induction board front and back flipped alaska ic1800w M399 suspect marked .jpg
Can you extrapolate more on how to indentify the pins on my board ?
By Mark August 7, 2012 - 2:55 pm
I am new to induction coils and know just enough about electronics to take things apart and put them back together again. So your hacking instructions are great for me. I apologize if the answer to my question is in your articles and I misread or missed it completely. I want to be able to heat a piece of metal that can range between 2 and 3 cm above the cook top. By following your manual mode instructions will adjusting the potentiometer allow an increase in distance from the coil or will the safety features built into the devise kick in and prevent an increase in distance. Thanks for all your work on this.
By Mexico Doug August 19, 2012 - 1:01 pm
Super hack job! KUDOS! THANKS from cyberspace for your efforts!
Just a little question … when you say the variable 10K pot can get down to a few hundred watts, do you have a better idea of at what lowest wattage input that you could stably run it? Specifically, I’ve got a sister cheapo to your 1800W and on the lowest setting it cycles on and off at 800W about 50% of the time, giving a rough 400W time averaged. It boils water. My goal is simply to have it at low enough power that it just warms it. A lower continuous limit of 300W would be perfect. Do you think this falls withing your parameters? (And 200W would be astonishing)…
Thanks again, can’t express enough appreciation for this hack.
By Ad November 2, 2012 - 1:26 am
Hello,
WOW this is a great article, i have also a cheap chines induction heater, but my version has a 8 pole ribon cable.
1-12 volt
2-GND
3- +5volt
4- Data
5- ?
6- ?
7- ?
8- ?
http://www.freebits.nl/view.php?filename=911IMG214.jpg
There is also no LM319 on the PCB, how can i measure what pin i can use….
By openschemes November 4, 2012 - 5:54 pm
Why don’t you peel off the “200D-BUP” sticker on the IC and see what the part number is. It doesn’t look like a ’4051, because ’4051 is 16-pin and your IC is 20-pin. Maybe it’s a microcontroller, but I don’t recognize that package with the two round spots at the top and bottom.
Anyone know whose chips have those round holes at the top and bottom? Old TI stuff, maybe? They had some chips with a smooth surface like that, but then they also had some with a rough surface.
By Ad November 2, 2012 - 3:52 am
There is a HCF4051BEY – SINGLE 8-CHANNEL ANALOG MULTIPLEXER/DEMULTIPLEXER on the control board…sow now i have to figure out wich pin controlling….
By Ad November 6, 2012 - 12:20 am
this is the chip under the sticker …
http://www.freebits.nl/view.php?filename=834IMG033.jpg
This is the text on it : CKM005nd20j
1210U BFS12393
Can’t find anything on the internet….
By openschemes November 6, 2012 - 9:39 pm
Found it! CKM005 is a 4-bit micro designed for induction cookers. It’s interesting enough that we posted your pictures (thank you, very nice pics BTW!) and a copy of the datasheet into a new article just for you.
http://openschemes.com/2012/11/06/induction-heater-with-ckm005-microcontroller/
So what cooker do you have? We want to buy one!
By Ad November 7, 2012 - 12:13 am
Hi there,
Nice to start a own article
, i have more pics to share….tonight at european time i will look at the sheet …..maybe i can do some measures on how much Hz the IGBT is switching.I you want you can put these pictures in this tread or the new one.
http://www.freebits.nl/view.php?filename=557IMG199.jpg
http://www.freebits.nl/view.php?filename=668IMG200.jpg
http://www.freebits.nl/view.php?filename=555IMG210.jpg
http://www.freebits.nl/view.php?filename=662IMG211.jpg
http://www.freebits.nl/view.php?filename=356IMG212.jpg
http://www.freebits.nl/view.php?filename=237IMG215.jpg
By Ad November 7, 2012 - 12:22 am
The heater …….
http://www.freebits.nl/view.php?filename=144heater.gif
By simonarun November 20, 2012 - 12:57 am
sir my induction stove is 10 minute run after display error message .what problem help me pls.
By radu yo3bzw romania March 29, 2013 - 7:02 pm
multumesc mult pentru documentatie mia fost de un real folos