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Background of my project
I want to create objects of metal. So I need to be able to cast a metal. Aluminium seems great as its strong, light weight, easy to obtain, but most importantly: its not toxic. So I want to be able to melt aluminium (933 Kelvin is the melting point).
I was thinking about induction. Its effective and easier than using liters of gas.
I tried to make my own induction heating circuit, but I keep blowing MOSFETs (royer oscillator design) when I ramp up the voltage to increase the power (my 12Vac versions work, but prepared for 48Vac they break down, let alone 230Vac. Now I spend enough money on fancy MOSFETs, so I bought myself a 2 Kilowatts induction cook-top that should get me melting some aluminium.
The cook-top has a 0.33uF (MKPH marked) capacitor in parallel with the original flat spiral coil, running at a varying frequency of 20-24Khz, depending on the distance of the steel pot on top of the cook-top. the specs of the original flat spiral coil: 24 windings of Lytz wire, 58mm inner diameter, 153mm outer diameter.
Now I replaced the flat spiral coil that I found inside the cook-top with a self wound solenoid of isolated wire (1.75mm diameter) with the following specifications: 143 mm height, 50mm radius, 32 windings => yielding an approximate induction of 53.75uH according to my calculations.
This works! I heated up a piece of heavy iron with aluminium inside until the aluminium melted. Though it was fun, my setup is far from practical. I used a water bath to cool the coil and glass jar inside the coil to keep the water away from the work piece and put the work-piece inside the glass jar. Finally the glass cracked, and the water bath in combination with a coil @ 230Vac isn't typically safe. The self wounded solenoid must be cooled because if the isolation would burn or melt, the chance of a short in the solenoid is high, probably breaking down the circuit of the cook-top.
So I need a solenoid that needs no isolation as the windings are distant from each other. Now I have a nice wounded solenoid of copper pipe with the following specs: 110mm height, 28mm radius, 11.5 windings. It should have an inductance of 3.03uH according to the same calculations I applied for the self wounded solenoid.
53.75uH / 3.03uH = Factor 17.73 less inductance. So can I apply this solenoid with less inductance if I replace the capacitance with 17.73 greater value? Which would be 0.33uF * 17.73 = 5.85uF.
If I replace a solenoid in a LC parallel circuit with a solenoid with X times less inductance, and increase the capacitance with the same factor X, keeping the resonance frequency the same, does the current stay the same as well?
EDIT: I tried calculating impedance of the overall circuit. But with 12Vac royer oscilator test circuits I build, the measured current differs from my calculations. I used the "Example No1" calculation from this website: http://www.electronics-tutorials.ws/accircuits/parallel-circuit.html