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Registered Member #5436
Joined: Sun Jun 24 2012, 01:44AM
Location:
Posts: 39
Hello,
I completed a quite nice looking driver about a couple weeks ago and it worked great at driving fly backs, reaching 5-6 inches with a fiery white arc. This used the 2 inductor system, IRFP260, and the standard setup. Power supply was mot rewound for 50 volts with varaic.
Today I tried induction heating. It worked quite well, heating up a bolt orange using a small 1/2 inch coil with about 14 turns, but then I made a 3/8 inch copper pipe coil, 5 turns, 6inch diameter. The latter worked quite poorly. After some time, the transistors failed, shorted source to drain.
Observations:
1. All parts of induction heater were cool to the touch 2. MOSFETS were heat sinker and air cooled (CPU heatsink cut in half) 3. MOSFETs did not suffer any explosive or fire buring type of failure
I suspect that the latter coil operated at a much too high frequency for the driver to operate correctly. I use a 2 uf cap bank. Would boosting the capacitance to 10 uf solve the problem? The inductance of the coil is too low for my meter to measure, less than 0.01 mh
Also, I have heard many stories of explosive MOSFET deaths, why didn't mine suffer the same? This has beenrepeated many times
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Either a too high frequency or a too high current, which causes the forward voltage drop of the transistors to increase above the gate threshold voltage and then it stops oscillating and both transistors turn on.
Registered Member #4497
Joined: Thu Apr 19 2012, 12:53PM
Location: Behind you
Posts: 62
Paul_J. wrote ...
Also, I have heard many stories of explosive MOSFET deaths, why didn't mine suffer the same? This has beenrepeated many times
Fireworks needs high current, like from 12V lead battery, i hink you had same problem, but you had to low current for explosion, and explosions are usually caused by low iductance of primary coil
Registered Member #5436
Joined: Sun Jun 24 2012, 01:44AM
Location:
Posts: 39
Hello,
Could this be rectified by first adding capacitance to the tank and raising the voltage of the zeners? I used 12 volt zeners, as the maximum voltage is 20 volts, could I replace them with 18 volt zeners, forcing the MOSFETS to turn off?
Registered Member #3282
Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224
I have built zvs induction heaters before. what happened you had parasitic oscillations returning back to the gate and opening it up and blowing it out. My experience you need to build a transformer to feed into the work coil. a 1: 1.5 ratio works well.
Registered Member #5436
Joined: Sun Jun 24 2012, 01:44AM
Location:
Posts: 39
Hello,
I tried MicroWatt's transformer, which only made the problem worse, and decreasing efficiency greatly.
Could the excessive forward voltage drop problem mentioned by Dr. DarK Current be rectified by the use of IGBTs? I was thinking about the HG20N60B or the 30N60, which would be better suited?
Also I have a new cap bank, comprised of 6 1uf MPK10 Wima capacitors. Is that fine?
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ZVS Universal Driver Malfunctions
