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High guys . I've been tinkering the induction heater in the past few days. I haven't killed a single mosfet since I've built it. I was able to push it up to 1500W then my rectifier shorted . The FETs were warm but nothing too serious (with fans turn on ). It takes about 4-5 seconds for a big bolt to heat up to red, and about 8-9 seconds to very bright red. But in this conditions my capacitors starts to warm a little bit. In my experiments i found out that the coil have a GREAT influence on the work of the heater. The two parts of it MUST be absolutely identical, all the wires connecting the coil to the other parts also must be identical. The fast diodes are also very critical parts. I've tried few different and when i changed them with slower the fets starts to heat up tremendously. With the new coil (that i burnt already ) i am running at 800w with almost no heating in the fets (after 2min of work the radiators were only slightly warm with fans turned OFF ). And one question - what exactly is the purpose of the inductor . I've changed the value allot and nothing changed in the performance ?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Huben Panev wrote ...
And one question - what exactly is the purpose of the inductor . I've changed the value allot and nothing changed in the performance ?
Cheers Huben
It's to provide a more-or-less constant current. The driver requires cross-conduction on the switches, without the inductor it would short out the power supply and/or explode.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
The driver requires cross-conduction on the switches, without the inductor it would short out the power supply and/or explode.
That is not as important as fact that parallel LC represenst low impedance to al frequencies apart from it's f0.
The cap represents a short circuit to squarewave voltage.
Huben: your inductor worries me if I see it right... have you paralelled coils with different numbers of turns on each toroid?
You should use one fat winding, and for 800W you will probably be fine with just one of those toroids. Have you scoped the circuit to see what frequency are you running at?
If you don't care about size of the circuit you could also use one big air cored choke and stop worrying about it.
The other very important thing, are you using separate power supply for gate drive?
In any case you should get rid of 470 ohm resistors and use something much smaller.
I'd prefer 33-50 ohm resistors for fast turn on time, they will get hot but still torelable for power level you are running.
And use carbon film resistors, several in parallel if needed, not wirewound resistors.
about the inductor - no the paralleled winding has the same number of turns (originally paralleled in the PSU ) and they are from 3 identical supplies. The big air inductor is a good idea but it will get just to big
No i haven't scoped the frequency but i will do it today.
No I am not using a separate power supply for the gates.
I don't see what is the problem with the 470 ohms resistors - the fets are just getting slightly warm (i think there isn't too much loses in slow switching)
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ZVS Induction Heater -800W
. I've been tinkering the induction heater in the past few days. I haven't killed a single mosfet since I've built it. I was able to push it up to 1500W then my rectifier shorted . The FETs were warm but nothing too serious (with fans turn on ). It takes about 4-5 seconds for a big bolt to heat up to red, and about 8-9 seconds to very bright red. But in this conditions my capacitors starts to warm a little bit.
) i am running at 800w with almost no heating in the fets (after 2min of work the radiators were only slightly warm with fans turned OFF ).
. I've changed the value allot and nothing changed in the performance ? 
