What is Induction Heating?
Ohm's Law states that in a simple electrical circuit, the strength of a current (I) flowing through a resistance (R) is proportional to the applied voltage (E). It is expressed by the formula:
Thus, if you increase the voltage, and resistance remains the same, the current will increase proportionately.
Resistance is well named, for it opposes current flow. The lower the resistance, the higher the current flow in the circuit, and hence the greater the power. This power (P) is the rate at which electrical energy is transformed into heat. It is expressed by the formula:
This heat can be put to good purpose and is the principle behind heating elements such as you will find in hair dryers and baseboard heaters. However, such direct production of heat is inefficient, localized, and difficult to control. For industrial purposes it is preferable to produce heat by using an induced current rather than a direct one.
With induction heating, we substitute an induced current for a direct one, which is of course the principle of the transformer. It works this way. Alternating current flowing through the primary coils of the transformer creates an electromagnetic alternating field. Since the reverse is also true, by placing secondary coils within that field, we will induce a current to flow through them. And depending on the respective number of electrical turns in the primary and the secondary, we can step up or step down the voltage levels. It is the voltage in the secondary turns which, when applied to heating elements, creates the energy to heat or melt metals.
Resistive Heating Illustrated
Induction Heating Illustrated
Current flow is induced in the secondary circuit by placing the secondary turns within the changing magnetic field created by the primary turns.