Flash_Cro

Hi all,

I was build 200khz half bridge inverter (cca 1kW), which have variable matching inductance, tank capacitor and work coil (10mm Cu) + lot of snubbers.So for iron(magnetic) stuff it works ok, (it heat iron very well at resonance), but I have problem with aluminium. It wont heat it (it become only worm 50°C), and inverter have big problems with "ringing" and self destruction .
I suppose that 1kW power is enough for melt some small piece of material but there is happening somethnig and I can't findout what...

I know that aluminium is highly conductiv, and it do not have magnetic characteristics like iron (probabbly is problem there).

Thus someone know which frequency to use for melting aluminium with inductive heater?

Thanks in advance,
Flash

eblc1388

No. The problem is not magnetic property but the first part of your statement. Induction furnace works by inducing current in the material to be heated. Aluminum is highly conductive and generate very little heat from eddy current loss.

Do you know of any induction furnace for copper?

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Flash_Cro

Hi,

You are right eblc1388 So that means that for aluminium I should use low frequency inverter which can produce more power, becouse I need bigger eddy currents. (I was forget on Lenz's law .....)

Regards,

Hero999

Alter the impedance matching network?

You want to effectively lower the output voltage and increase the current to melt the aluminium.

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Flash_Cro

Hi,

Well I was alter matching network, and on resonance I can get big currents on low voltage, but on scope I see (parasit osc.) that inverter is close to explode...
Inverter voltage and sine shape (on scope) is same with or without aluminium insde of coil on 200 kHz, and inverter likes to go in oscilations which on the end kill mosfet's.
I will try with low frequency about 5-20 kHz. On this frequencys I can easilyer control mosfet's and osciltions, or even use igbt's.

Regards,

Hero999

If you lower the frequency, you'll have to add more turns to the coil and use a larger tuning capacitor; there might be other modifications that you'll also have to make but we can't really advise you as we don't have access to the schematic.

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Flash_Cro

Hi,

Here is schematic:
driver-jpg.jpg

I know that I will must change components, that is not problem only thing is which frequency is the best for Al melting.
Regards,

Hero999

I can't say I'm the best person to advise you on this as I haven't had any experiance with this sort of thing.

All I can say is that Lm, Lx and Ct probably need increasing to reduce the resonant frequency. but you probably already knew that.

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shirazmacuff

i don't have much knowlege about induction furnace, but i have seen one used for aluminium. it was a selfmade furnace and they used a steel crucible instead of the carbon type. Please seek additional information on the details before you try it.