Induction Heating

Induction cookers, furnaces, stoves and all that jazz are now widely used. You put your metal saucepan on top of an innocent looking glass plate and it magically heats your food with no flame and almost no waste heat.

They are able to heat certain metals up to their melting points, and that is very hot, obviously...

How they work? Well...

Image courtesy of Proidee UK

Image courtesy of Infolytica

When an alternating electric current is passed through a coil, the coil creates a magnetic field. The magnetic lines of flux cut through the air around the coil. If a ferrous material, such a solid bar of iron is inserted into this coil, certain effects known as eddy currents are induced to flow in the metal bar. This causes localized heating, and ultimately heats up the metal bar.

In an induction heater, the coil is known as the 'work coil'.

Remember the Ignition coil driver of mine? It just so happens that it is designed to send an AC current of variable frequency into a coil, and that made it perfect for induction heating.

So to make the work coil, a meter or so of #16 gauge copper wire was tightly wound with a total 40 turns.

The coil driver was then modified to suit the new work coil (actually when the picture was taken, it had already been burnt black in many places).

Results! With an input voltage of 24V, at 3A, it takes about 30 seconds to heat a small bolt red hot.

Notice how only the section of the bolt inside the work coil is experiencing heating effects. I had to mount the work coil on a ceramic (tile) base as it had started to melt bits of my work bench.

A hexagonal screw in the red hot zone. Estimated at ~700 degrees C, from the colour of the steel.

Input frequency is ~300kHz for the coil. This seems to deliver maximum heating power.