InductionHeater

Project InductionHeater
Status	In progress
Contact	smeding, gori
Last Update	2014-10-16

We're working on an induction heater that can be used to heat anything conductive to high temperatures. The plan is to try to use it for forging steel and melting aluminum.

Here are some examples of what a device like this is capable of:

• https://www.youtube.com/watch?v=0HdbKKvOiWU
• https://www.youtube.com/watch?v=l7fArOvXhQY

Specs

• Input power: 3.5kVA, standard single-phase mains
• Frequency: 10 - 100kHz

Inverter circuit

The basic power system looks as follows:

230V mains input is rectified, then filtered slightly and chopped up into a variable-frequency square wave (or modified sine wave) using an H-bridge made of IGBTs. This is fed into a coupling transformer, which turns this high voltage, (relatively) low-current waveform into a higher-current, lower-voltage one more suitable for the system. This is connected to a series-resonant circuit comprised of the heating coil and a tank capacitor.

The resonant frequency changes depending on workpiece geometry, coil geometry, workpiece temperature, etc. etc. so this needs to be tracked by a controller.

The secondary side of the transformer dissipates a lot of power (there are potentially hundreds of ampères flowing there, so fairly large ohmic losses) and will need to be water-cooled to prevent it from getting too hot.

BOM

Some of the components have already been scrounged together. Thanks to benadski for acquiring an induction cooktop that contained many useful parts!

Component	Cost	Comments
Bridge rectifier		Salvaged from cooktop
inverter IGBTs		Salvaged from cooktop
Tank capacitors		Salvaged from cooktop
DC link filter capacitor		Salvaged from cooktop
Gate drive transformers		Salvaged from cooktop
Coupling transformer core(s)	€42	http://www.aliexpress.com/item/100mm-x-65mm-x-20mm-Ferrite-Rings-Toroid-for-Filters-Coils/879528762.html, we need 3 of these for enough core area
Litz wire for transformer primary		Salvaged from cooktop
Copper tubing, 15mm OD * 5m	€30	Conservative estimate from hardware store -- can probably do better. Will need more than 5m for larger work coil.
Copper pipe compression couplings 15mm * 2	€12	Can probably do better
Water cooling pump	€5	Cheap brushless water pumps abound on eBay; e.g. http://www.ebay.com/itm/321431156285
Water cooling connections	?	Need to find best solution
Water cooling radiator	?	Car engine radiator goes €10 - €20 on Marktplaats. Possibly from scrapyard?
Gate driver *4	€5	e.g. http://nl.farnell.com/microchip/tc4420coa/ic-driver-mosfet-6a-smd-soic8/dp/1292283
Control electronics	€10	Microcontroller, displays, assorted resistors&capacitors
Total	€104

Pledges

So far, the following has been pledged:

• Gori: 50 euro
• Flok: 10 euro
• Walter: 50 евра
• FooBar: €20
• bertrik: €10
• Semafoor: €20
• Morphje: EUR 10 (and driving to the hardware store if needed)

Total pledges: €170