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Calculate Induction Heater LC Resonance Frequency and Current


In the previous post we elaborately learned how to design an induction heater circuit, continuing ahead here we learn how to calculate induction heater LC resonance frequency, and its wire current handling capacity.


The previous post explained the fundamental secrets behind developing a low cost yet effective induction cooktop at home, in this article we will see how this can be implemented by specifically calculating its crucial parameters such the resonance of its tuned LC circuit and the correct dimension of the coil wire for ensuring an optimal current handling capacity.

What is Resonance in Induction Heater LC Circuit


When the capacitor within a tuned LC circuit is momentarily charged, the capacitor tries to discharge and dump the accumulated charge over the coil, the coil accepts the charge and stores the charge in the form of magnetic field. But as soon as the capacitor has discharged in the process, the coil develops an almost equivalent amount of charge in the form of magnetic field and it now tries to force this back inside the capacitor, although with an opposite polarity.



Image courtesy: 

https://en.wikipedia.org/wiki/LC_circuit#/media/File:Tuned_circuit_animation_3_300ms.gif

The capacitor is again forced to charge but this time in the opposite direction, and as soon as it's fully charged, it yet again tries to empty itself across the coil, and this results in a back and forth sharing of charge in the form of an oscillating current across the LC network.

The frequency of this oscillating current becomes the resonance frequency of the tuned LC circuit.

However due to inherent losses the above oscillations eventually die out in the course of time, and the frequency, the charge all come to an end after sometime.

But if the frequency is allowed to sustain through an external frequency input, tuned at the same resonance level, then that could ensure a permanent resonance effect being induced across the LC circuit.

At resonance frequency we can expect the amplitude of the voltage oscillating across the LC circuit to be at the maximum level, resulting in the most efficient induction.

Therefore we can assume that to implement a perfect resonance within an LC network for an induction heater design we need to ensure the following crucial parameters:

1) A tuned LC circuit

2) And a matching frequency to sustain the LC circuit resonance.

This can be calculated using the following simple formula:

F = 1 ÷ 2π x √LC 

where L is in Henry and C is in Farad

If you don't want to go through the hassles of calculating the resonance of the coil LC tank through formula, a much simpler option could be to use the following software:

LC Resonant Frequency Calculator


Calculating Wire Size for Induction Heater Work Coil


Once you have calculated the optimized values of L and C for the tank circuit of the induction heater and evaluated the exact compatible frequency for the driver circuit, it's time to calculate and fix the current handling capacity of the work coil and the capacitor.

Since the current involved within an induction heater design could be substantially large, this parameter cannot be ignored and must be correctly assigned to the LC circuit.

Using formulas for calculating wire sizes for an Induction wire size may be a little difficult especially for the newcomers, and that's exactly why a special software for the same has been enabled in this site, which any interested hobbyist can use to dimension the right size wire for your induction cooktop circuit. 


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2 comments:

  1. sir please can u give me a comparator circuit using 555 timer i want to make a comparator using 555 time not lm939

    ReplyDelete
    Replies
    1. you can try the last circuit from the following article

      http://www.homemade-circuits.com/2012/01/how-to-make-light-activated-day-night.html

      Delete

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