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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
You might need some kind of a resonant circuit (parallel LLC or series LC) to actually do something, if you use only an inductor, there will be a lot of reactive power and you'll at most get few tens of Watts of heating power.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
adding a capacitor in parallel with the work coil will give a simple resonant circuit. the capacitor and coil will have a resonant frequency, but this will vary with different workpieces and will vary as the workpiece heats up.
most circuits will also have a series capacitor and/or a series inductor, at minimum.
The idea is to match the resonant frequency of the work coil/parallel capacitor to the frequency of the transformer. There are basically two ways to do this, one is to use variable capacitors, and maybe a variable series inductor. The other way is to use a feedback loop from the resonant circuit to drive the transformer at the same frequency. This is the method that most people use for induction heaters. It is also the method that the Mazilli ZVS circuit uses.
If your transformer outputs a fixed frequency you'll have to match the coil/capacitor pair to that frequency using variable capacitors, etc.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
You can not put a capacitor directly in parallel to the transformer, because the output is square wave and you would destroy the driver circuit with too much peak current.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Interesting idea, could work. You would need to tune it so that the frequency matches as others have said, one method I would use is a constant current ie LM317 in series with power resistor driven from a bridge rectifier on the output to adjust the current until resonance is achieved.
Feel free to slap me for coming up with such a kludgy workaround
-A Current topical project:- Lord Voldemort magic wand with Tesla Coil inside.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Platinum wrote ...
So what do I do?
Sorry, I'm new to making these.#
You said add a resonant circuit?
Hmm, I don't know what that means, but is it to higher or lower resonant frequency?
Basically, make a work coil with a series capacitor that both resonate together at the frequency of the power supply. First you should use a stepdown transformer though, to match the impedance of the work coil. Something like 10 turns on the primary and a few on the secondary, just experiment. Oh, and to calculate resonance you can use Javatc:
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Dr. Kilovolt wrote ...
You can not put a capacitor directly in parallel to the transformer, because the output is square wave and you would destroy the driver circuit with too much peak current.
I am aware that more components would be required than just a parallel capacitor, but thanks for clarifying that point.
A series inductor had already been mentioned. I think this would tend to convert the output to a sine wave form, but I'm not an expert here.
I had suggested that additional components, eg, series capacitor, series inductor would be needed, and was hoping others would contribute.
I personally think that the best route here would be to follow one of the Mazilli based induction heater designs. This would give a good grounding for a beginner project. (I hinted at this above)
I believe Inducktion (I think it was Inducktion, it may have been someone else, Camp Badger, maybe) posted something recently on this subject that achieved reasonable results.
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