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Registered Member #3859
Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179
Hello. I bought a ZVS flyback driver - like circuit on aliexpress in order to build an induction heater. The circuit looks something like this.
I conducted an experiment where I dropped a ball bearing into a test tube with water and waited for the water to heat. Then I replaced this ball bearing with a softer steel machine screw. I tried to calculate how much power actually went into heating the water from ambient temperature to 100C, but failed to do so.
This system took almost thirty minutes to boil the water. I tried different coil shapes. 60 grams * 80 degrees change * 4.18 = 20064 Joules = 5.57 watt*hours Thus only 12 watts were involved in heating of the water. Out of how many? Where are the losses?
What would be the ideal coil parameters? Do I need more capacitance, connected in parallel to the inductance coil? as shown here:
What would it take for me to get the most induction heat out of this device and to minimize the losses produced by high current flow?
Thank you.
- everything i tried - better coil - not very good coil - bad coil
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
your caps should have the lowest ESR you can find and may be a problem. your tank circuit does resonate with the oscillator you have provided. maybe you need more power to it. maby adding more caps will decrease ESR enough. have you tried to see with an oscilloscope?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
It is hard to tell dimensions, but in addition to everything else your coil diameter may be too wide that you are not getting good coupling with the work piece.
Registered Member #61905
Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23
tarakan2 wrote ... What would be the ideal coil parameters?
It depends on the circuit you bought, on the load, and on your power supply. Can you provide more details? What circuit board are you using? Does it use a center tapped work coil? What are the capacitor values? What are the capabilities of the power supply that you're using? Is your power supply adjustable? What are you trying to heat? If you just want to heat little pieces of steel, a coil that's pretty close in size to the load would work better than one that's much bigger.
edit: I see the board in your first picture, and looking at the components it seems like you need a center tapped work coil and you have ~0.6uF of capacitance. Based on what see in your other pictures, I would suggest trying a 4+4 turn work coil that's close in size to the object. Use heavy gage wire, or you can twist multiple strands of a lighter wire together in parallel (aka litz wire). Also the coil needs to be close to the capacitors. It looks like the wires connecting your coils to the board are pretty small gage and extra long. There is a high current resonating between the coil and the capacitors, so the coil would work better if made with heavy gage wire and connected straight to the circuit board. If you look at one of your other pictures you can see their work coil is very few turns of copper tubing that connects straight to the capacitors a short distance away. Let us know how it goes...
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Inductive heater
