You might have come across many DIY induction heater circuits online but nobody seem to have addressed the crucial secret behind implementing a perfect and a successful induction heater design.
Before knowing this secret it would be important to know the basic working concept of an induction heater.
An induction heater is actually an extremely "inefficient" form of electrical transformer, and this inefficiency becomes its main advantageous feature.
We know that in an electrical transformer the core needs to be compatible with the induced frequency, and when there's an incompatibility between frequency and the core material in a transformer, it results in the generation of heat.
Fundamentally an iron cored transformer will require a lower range of frequency around 50 to 100Hz, and as this frequency is increased the core may shown a tendency of getting hotter proportionately. That implies, if the frequency is increased to a much higher level may be over 100kHz would result in the generation of extreme heat within the core.
Yes, this is exactly what happens with an induction heater system where the cooktop acts like the core and therefore is made up of iron material. And the induction coil is subjected to a high frequency, together this results in the generation of a proportionately intense amount of heat on the vessel. Since the frequency is optimized at significantly high level ensures a maximum possible heat on the metal.
Now let's proceed and learn the important aspects that may be required for designing a successful and technically correct Induction heater circuit. The following details will explain this:
The two bare basic things required for building any induction cookware are:
1) A bifilar coil.
2) An adjustable frequency generator circuit
I have already discussed a few induction heater circuits in this website, you can read them below:
All the above links have the above two things in common, that is they have a work coil and a driver oscillator stage.
For designing an induction cookware, the work coil is supposed to be flat in nature, therefore it must be bifilar with its configuration, as shown below:
The above bifilar coil structure was design by Tesla way back in the year 1894, but the concept still holds good for all induction related transmissions.
The same coil which is shown above can be effectively implemented for making your homemade induction cookware.
For optimum response and low heat generation within the coil make sure the wire of the bifilar coil is made using many thin strands of copper instead of a single solid wire.
Thus, this becomes the work coil of the cookware, now the ends of this coil simply needs to be integrated with a matching capacitor and a compatible frequency driver network, as shown in the following figure:
So far the information should have enlightened you regarding how to configure a simple induction cookware or an induction cooktop design, however the most critical part of the design is how to resonate the coil capacitor network (the tank circuit) into the most optimal range so that the circuit works at the most efficient level.
Enabling the coil/capacitor tank circuit (LC circuit) to operate at their resonance level requires the inductance of the coil and the capacitance of the capacitor to be matched perfectly.
This can happen only when the reactance of both the counterparts are identical, that is the reactance of the coil as well as the coil are approximately the same.
Once this is fixed you can expect the tank circuit to operate at its natural frequency and the LC network reaching the resonance point. This is called a perfectly tuned LC circuit
You may be pondering regarding what is resonance of an LC circuit.?? It may be explained in the following manner:
We will learn the details in our next post which will explain how to calculate LC resonance frequency, and current of an induction heater coil.