Induction Heating


Induction cooktops used to be mythological items which existed only in dreams. Now they are common-place in kitchens and stoves around the world. Induction cooktops are fairly unique kitchen appliances that have become commonplace in many households.

Magically, the innocent looking piece of glass which you call an induction cooktop heats your food with no smell, no noise, no obvous heat source - nothing!

A typical induction cooktop
(Image courtesy of Proidee UK)

When an alternating electric current is passed through a coil of wire, 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, electrical currents known as eddy currents are induced to flow in the metal bar. This causes localized heating of the bar.

In an induction heater, the coil is known as the 'work coil', and the ferrous material usually presents itself in the form of a metallic saucepan.

But lets start from scratch and see what we can do with some DIY induction heating!

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 and tuned in frequency to suit the new work coil.

Work coil made from enamelled copper wire

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

Notice that only the section of the bolt inside the work coil is experiencing heating effects - heating is very localised.

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°C from the colour of the steel.

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

And... remember those 'bullets' from the coilgun? Well here is one heated red hot. These took a bit longer than the screw to heat up, presumably due to their larger volume. Perhaps also something to do with the material too.

Unfortunately, during the last run of the induction heater, a MOSFET exploded.

Someday I would like to get a bigger, better induction heater going to hopefully melt some steel.




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