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I have been building an induction heater based off this schematic. I have tried using irfp250m mosfets. Works like a charm. But whenever I put a too big piece of iron inside the coil, the mosfets soon self destruct. However if I place a smaller piece in the coil, it heats up orange hot. The power supply isn’t the problem here. It’s a 48v 50a telecom switching power supply. So I wanted to increase the amount or iron I can put in the coil. I went out and got me some more unique mosfets. First one I got is a 2SK1812. Worked perfectly while idling, however self destructs when something is placed in the coil. Even the smallest piece that worked with the irfp250m. The 2sk1812 is rated for a higher voltage and amperage, so why didn’t it work? Is it the RDS on? Does the switching speed(Trr) matter?

Ok so I was like on these won’t work so I replaced the blown 2sk’s with 2 beefy APT43M60L 600v 45A N ch mosfets. These ones worked but got hot really fast. That is definitely the RDSon causing that. But still doesn’t work with the same chunk of iron that the irfp250m mosfets did well with. The apt43’s also self destructed.

So why did these problems happen? And what are some mosfets that could work with high power induction heater?

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Two things for you to check.

1) Ensure that the power supply rise time is FAST. Generally don't switch the power supply on with the inverter connected, the inverter can get into a linear mode that prevents fast switching of the MOSFETS and leads to destruction. Connect the inverter to an already powered and enabled supply.

2) Check your inductors are not saturating at your maximum current, as saturating inductors effectively look like a short. So you get full power supply voltage across a MOSFET in the ON state - leading to overheat and destruction. The circuit will work OK at idle, and low power, but at high power will self destruct. Did you make the inductors? Commercial inductors specify the saturation current, but if you just used any old toroid, you will not necessarily be able to predict the saturation point.

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  • \$\begingroup\$ +1 This is a good answer! :) Instead of recommending a particular product, you actually told the OP what specifications they should look for. \$\endgroup\$ – KingDuken Jun 12 at 3:04
  • \$\begingroup\$ I took 2 black inductor toroidal cores from an electric pressure washer board and wound enameled copper wire around it till I got 169uh on my LCR. Here is my setup. prnt.sc/o0qb1l Here is the inverter prnt.sc/o0qb9u as you can see the 2sk is scorched. \$\endgroup\$ – ElectronicsNoob Jun 12 at 4:08
  • \$\begingroup\$ Also, maybe a linear type rectifier power supply would work better? And what specifications for mosfets point toward good induction heater quality? I know the rdson is a big one. \$\endgroup\$ – ElectronicsNoob Jun 12 at 4:14
  • \$\begingroup\$ To see whether your toroid will saturate, you will need to do some calculations, and know more about the core you have. I can't help with that, but here's a link to some information that will point you to how much power you can put through a toroid of a certain size and type: vkham.com/Info/ferro/tut_3.html \$\endgroup\$ – elchambro Jun 12 at 22:46
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    \$\begingroup\$ An analog supply with the power you need will be large and expensive. Switchmode supplies are fine, just be sure to keep the supply turned on, and have a switch between the output of the supply and the inverter, and use that to power on/off. See these links for some other hints (some in slightly dodgy English) banggood.com/… and spaco.org/Blacksmithing/ZVSInductionHeater/… \$\endgroup\$ – elchambro Jun 12 at 23:00

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