Induction Heating for aluminum and copper

[brushhead]

Ah ok c_mitra I had missed that detail. In that case you are probably going to have to run this at probably 200kHz if the work piece is very small. This will mean that the coil might end up being a turn or two. Silicon Carbide MOSFETs are ideal for this. I wish they existed when I was developing IH Inverters back in the late 1990's! Life would have been a lot simpler and we could have got shut of Valves sooner!

 

[badea]

Ah ok c_mitra I had missed that detail. In that case you are probably going to have to run this at probably 200kHz if the work piece is very small. This will mean that the coil might end up being a turn or two. Silicon Carbide MOSFETs are ideal for this. I wish they existed when I was developing IH Inverters back in the late 1990's! Life would have been a lot simpler and we could have got shut of Valves sooner!

Thanks for your help
i will try to apply 200Khz with standard Mos or IGBT, but i don't know if IR2110 drivers can handle this frequency!!
as i understand, with 200Khz i need a small working coil and a small parallel capacitor, am i true or not?
let's consider a working coil will be 2uH, F=200Khz, that's mean a parallel capacitor should be 317nF, is it true or not?

regards,

 

[Warpspeed]

You can use an IR2110 to get isolation, but you will probably need to put a much more grunty non inverting gate driver between the IR2110 outputs and each gate.

317nF and 2uH will resonate at around 200 Khz
Both will have a reactance of about 2.5 ohms
For target Q of 10 driving impedance will need to be 25 ohms
For 10Kw excitation that is about 500v rms and 20 amps rms

Both coil and capacitor will need to carry 100Kvar circulating current, perhaps 200 amps rms

That is the expectation. Getting it can involve a bit of fine tuning and adjustment.

 

[badea]

For target Q of 10 driving impedance will need to be 25 ohms

How to achieve 25 ohms impedance?
if i added a series 35.3nF capacitor with resonant tank (impedance equals 22.5 ohm @ 200kHz) it will work or not?
i appreciate your help

regards,

 

[Warpspeed]

The 317nF and 2uH values you originally suggested already has a load impedance of 25 ohms when the Q is ten.
No need to do anything else, except drive it to 500v rms and 20 amps to get your 100 Kw circulating energy.

You can then feed 10Kw through this into the load, but the circulating energy will stay at about ten times that (Q=10)

 

[brushhead]

Again my comment earlier about water cooling of the Tank capacitor and the working coil becomes clear...the connecting hoses need to be 'carbon free' for obvious reasons and very clean water with a decent amount of pipe between potentials, like more than 2m.

Silicon carbide FETs are a lot easier to drive than normal Silicon devices.

 

[docs]

I went through all this myself some time back.

dear Warpspeed,

Recently I got also interested in IH.
Searching through the internet I came across an old forum thread where you (if you are the same Warpspeed ) partially documented the building of your induction furnace.
I got the impression if a DIY-er can ever build a usable induction furnace, you can.

May I ask how far did you get with your project?

I happen to have practically all necessary components for such a project including power semiconductors, cooling unit and a (hopefully) suitable tank capacitor, the only missing part is the proper knowledge :lol:

I choose the frequency to be also around 20 kHz, mostly because my tank capacitor is 10uF.
Power is coming from a regulated DC power supply (max 160V, 93A, I know it is not ideal, but maybe a good starting point).

The tank is driven by four IGBT-s through a coupling transformer.
The oscillator is TL494. My original idea was to regulate the power by PWM, that's why I used TL494, but later I discowered that this is not suitable in this kind of application. Still it is good enough for oscillator since it has push-pull output with dead-time control.

I plan to use PLL for freq control.

I got to the point to be able to heat a piece of metal red-hot (feeding 1.5kW into the circuit, but I know the efficiency is really bad), but of course it is still far away from the final goal.

I would be glad to hear about your experiences in DIY induction furnace!

rgds, Jozsef

 

[badea]

Dear Friends:
After reading of several references about IH i found that a starting point of designing of any IH is a coil design, because a coil will handles the required power and transmits it to the load, so if you design your suitable inductor, after that you can choose capacitance and frequency required for that.
let's consider you designed a coil and choose a frequency, after that you can select required capacitance

i think this is a good way to start design.
what do you think?

regards,