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Yeeeeha! Microprocessor controlled induction heater

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IamSmooth

Mon Mar 15 2010, 01:57AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I have successfully made a microprocessor controlled induction heater. My goal was to have a unit that will locate, lock and track resonance without any user input, and with any coil or workpiece.

The video shows how accurately and cleanly the circuit holds onto the resonant frequency. The range is 50 khz - 100 khz, but I can set it to anything. However, I have finer resolution if I keep the range tighter. Right now I can move in 12 Hz increments.

My next step is to connect it to 220v mains and see how hot I can get things. Then, I want to try and levitate a solid piece of steel and copper.

Bjørn

Mon Mar 15 2010, 04:01AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

That is excellent, it seems to work perfectly. Don't forget to explain how you did it.

IamSmooth

Mon Mar 15 2010, 04:04AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

I plan to post schematics and have an updated video when I get it set up.

Conundrum

Mon Mar 15 2010, 08:21AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

nice! :)

something like this would be handy for a reprap liquid metal dispensing nozzle...

-A

uzzors2k

Mon Mar 15 2010, 01:01PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Neat! Was this more enjoyable to design than the analog induction heater? I've never given digital control loops much thought, but there's so much more you can do with them that they must really excel in applications like this. What kind of microprocessor are you using?

IamSmooth

Mon Mar 15 2010, 01:21PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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ATMega328

GeordieBoy

Mon Mar 15 2010, 02:39PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Cool. What did you use for the RF source driving the inverter? Direct PWM out of the micro at the IH frequency, an analogue VCO controlled by the micro, or a digital DDS chip?

Have you implemented current/voltage limiting in your software controller also? You don't always want the inverter to pump full power into the tank circuit at it's resonant frequency. A typical example of this situation would be if the workpiece is removed.

-Richie,

IamSmooth

Mon Mar 15 2010, 05:49PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

Well. I have a small setback. It seems that as I increase the input voltage at resonance the chip gets reset. It just stops. The only way I can recover is if I take the microprocessor out and reprogram it.

Any thoughts? Do I need to tie all inputs that aren't being used to ground? Do I need an optocoupler to isolate my pwm output to the opamp? More decoupling capacitors somewhere?

Nicko

Mon Mar 15 2010, 06:06PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

IamSmooth wrote ...

Well. I have a small setback. It seems that as I increase the input voltage at resonance the chip gets reset. It just stops. The only way I can recover is if I take the microprocessor out and reprogram it.

Any thoughts? Do I need to tie all inputs that aren't being used to ground? Do I need an optocoupler to isolate my pwm output to the opamp? More decoupling capacitors somewhere?

More than decoupling I would have thought - have you scoped the power lines for the uP? also, with all that RFI, tie everything down to GND that's unused (nothing floating) anywhere, and screen & filter like crazy. One thing I learnt early was to use a completely separate regulator & filtering for the uP - don't share it with anything else! You can make nice boxes with FR4 board soldered up - a common radio amateur trick - e.g. see

and

etc.

I use the ATmega168PA at lot (will be using the 328 as they are essentially the same chip) with a TC for something I'm, working on, and I'm probably going to optically isolate all my I/O so that the uP can live safely in what is an extremely non-uP-friendly environment...

Another thought: Check your ground path and make sure nothing else is returning current anywhere near your uP - use a "star ground" configuration.

cjk2

Mon Mar 15 2010, 09:54PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

Could it be something as simple as a signal coupling back to the reset pin on the Atmega? Use a pullup resistor on the reset pin and see if the problem goes away.

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