James wrote ...

The ZVS driver is by far the simplest, you really need a lot of power to do induction heating.

John DeArmond's "Roy" induction heater that I posted the other day is the simplest cheapest design I've found. It's essentially a Mazzilli driver with some modifications to make it more robust. His older revisions are even simpler and will work at lower power. You will need some burly 1200V IGBTs or mosfets to run straight from mains but those are getting cheap. I got 10 of the ones he used for 20 bucks on ebay.

Hop on craigslist or freecycle and find an old UPS or car battery charger if you want a big transformer to run it. You'll need that for anything that isn't straight mains powered. The ferrite core for the matching transformer can be salvaged from a flyback.

Marko wrote ...
you'll also need to spend several hundred bucks on a proper conduction cooled capacitor as well.

Marko wrote ...

The matching transformer allows you to convert some voltage to current, so that the transistors don't have to carry the full current passing through the work coil. In effect it's like a gearbox allowing a motor to produce enormous torque by reducing the speed. The current in the work coil can be tens to hundreds of Amps without needing exotic mosfets. It also dramatically reduces the effect placing different objects within the work coil has on the operating frequency and lets you use a work coil without a center tap. Almost any large ferrite will work to some extent, like I said, you can take one from a dead flyback or take apart the transformer from an ATX power supply.

This is one of reasons why a matching transformer is used with series induction heaters, but not very true for ones with parallel circuits. In these the transformer is either 1:1 or a small stepdown (2:1 or so) and it's primary purpose is isolation.

Theorethically you could run a ZVS driver from mains at 1200V staight into work coil, but I'd definitely use a tansformer simply for isolation reasons.

In any case if you want to get into serious induction heating, apart form the big ferrite cores (look at my soviet ferrite thread and search the store for gigantic soviet toroids), you'll also need to spend several hundred bucks on a proper conduction cooled capacitor as well.

The other problem with ZVS is, that when ran from high voltages, it frequently tends to blow up. That's the main reason you don't see anybody using it.
You might have fun heating some bolts red hot with it powered from a rewound mot or so.

Marko

James wrote ...



I'll post this in this thread

He determined why the ZVS driver had a tendency to explode and came up with a refined design that solves this. The resonant capacitor he uses is 3-4 bucks in small quantities and the circuit is capable of running continuously at ~1kW and pushing up on 2kW for short periods. He's currently developing a much larger heater that can do >8kW but for most people the basic design is likely more than enough.

His design can be built for under $100 if you buy everything retail, and much much cheaper if you do some scrounging and can get by with somewhat lower power. Take the basic ZVS circuit, add some real mosfet gate driver ICs and a schmitt trigger flip-flop and the reliability is greatly improved at higher powers. The stock "Mazzilli" circuit is good for ~60V input though if you use 3W resistors. I found I can easily heat screws and nails and such red hot in a few seconds using parts salvaged from old CRT monitors. As I said already, I *strongly* recommend starting with the proven "Mazzilli" circuit since it's dirt cheap, ridiculously simple, and proven to work. When you reach the limits and want more, tweak it and experiment, or build John's design as it's proven robust and also quite simple.

Most importantly, have fun and don't burn yourself.