[SOLVED] Induction heater, Serious, re flesh absorption

Hello,

I ordered from ebay ZVS induction heater which is meant to run under 48VDC and I tested it with lab power 30VDC and 5A. It looked like it was shorted as it draw 5A immediately when powered. I've read that it needs to be plugged in when power is on so it will start to oscillate so I did and still looked like it was shorted. Soon my wrist felt heat and I shut it down. I immediately started thinking that could this thing actually be broken and send microwaves to heat tissues in my hand? There were nothing inside the copper coil to draw that amperage.

Please someone who understands these devices that is it possible that this thing worked like microwave oven or is it even possible? Device that I bought:
https://www.ebay.com/itm/20A-1000W-ZVS-Low-voltage-induction-heating-board-module-Flyback-driver-heater-/171906345819?hash=item28066aab5b:g:mj4AAOSwZd1VXgkW

It would not be microwave but rather VHF , but still if there is no iron core inserted, it will couple to any stray tissue nearby.

the idea is to couple a lossy medium near the coil, to absorb the power, not your hand. Iron has a lot of Eddy current loss so it will absorb power.
If your hand was a lossy as iron core, it would get much hotter quickly.

Veketti said:

is it possible that this thing worked like microwave oven or is it even possible?

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Regardless of the frequency range generated by the circuit, it is strongly recommend that you arrange a metal housing to shield noise emissions to nearby, such as are made in microwave ovens, otherwise there will be a strong chance that this device, which certainly is not properly certified, it may interfere in a wide range of signal transmissions in the neighborhood.

From the link you provided.

"9. When made with switch power supply, because of the high power generally has function of soft start, namely just powered on the output voltage is slowly rising, while if before the voltage up to 12v connected induction heating circuit, will not work and burn MOS tube. So voltage reaches more than 12 v connected induction heating circuit. "

I think what that means is any power supply over 12 volts must be soft start or the power mosfet will burn out.

I think you should have started it with a current limiting resistor and then use a relay to bypass the resistor.

Thanks for the replies. Should I interpret this so that it will not do any tissue damage? Even if something failed it cannot be turned to dangerous? I see many videos in youtube where people are using successfully these so assuming as long as if it did work it is not dangerous. I don't wanna loose my hand if there is a slight change that happening. Surely I didn't put my hand inside the coil.

No, it is not possible for this item to act like a microwave oven. This works close to the 27MHz (open frequency) range and uses the same principle as industrial induction furnaces work (they usually start at 100KW). The same principle is used in Induction heater (see the item here: https://www.amazon.com/Inducto-A79-...d=1453789551&sr=1-4&keywords=induction+heater).

The heat is produced in the target by eddy currents. Perhaps you can even melt a piece of iron in a quartz test tube but not Cu or Al. It will not heat a piece of glass or wood. Perhaps you can see the specifications of the power transistors. The Cu coil should have been hollow to allow passage of cooling water to cool the tube (what else?) and prevent it from melting. Skin effects makes all the current to move close to the surface and the hollow core does not affect the performance.

The oscillator is free running Hartley or Colpitts type in general. Perhaps you can tell us more.

This works close to the 27MHz (open frequency) range and uses the same principle as industrial induction furnaces work (they usually start at 100KW). The same principle is used in Induction heater (see the item here)

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No, these are completely different devices. Induction cookers are operating in the 50-100 kHz range and heat ferromagnetic material exclusively by means of hysteresis losses. RF induction heaters can heat all kind of metals utilizing eddy currents, as said.

The E field of a 13.56 or 27.12 MHz high power transmitter coil can cause a certain amount of dielectric losses, in so far it's possible that you feel some heat. The power density should be too low to cause serious harm.

It seems to me that the device is sold with effectively no specification. Do they ship a schematic? Safety instructions, e.g. regarding dangerous high voltage?

FvM said:

exclusively by means of hysteresis losses. RF induction heaters can heat all kind of metals utilizing eddy currents, as said.

The E field of a 13.56 or 27.12 MHz high power transmitter coil can cause a certain amount of dielectric losses, in so far it's possible that you feel some heat.

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I believe both eddy currents and hysteresis loss are involved. My steel pan that is practically non-magnetic works as usual. I am, of course, wrong about the frequency. I tired to use my radio to check the frequency but could not...

There are dielectric heaters too that use the dielectric loss to heat a material- many plastic welders work on this principle.

Thanks everyone for your kind help. Sorry, in a hurry I opened this thread to wrong area as there were more suitable ones than this under Analog design. Mod/Admin can move if wish to do so.
Here are the components that this device has. It seems very simple.



Those two white ones seem to be 5W 470ohm resistors.
Also four diodes, two small resistors and of course those two toroid coils.

I dare to try it again when there's no danger but, any idea how could I get it to work, it seems shorted no matter how I supply current to it?
There were no instructions whatsoever supplied with it. All was what was said in that ebay page and youtube videos with others who had the same unit and operating it.

A 1000W device working around 50V is expected to draw around 20A. If there is no load (just put an old screw driver in the coil) the transistors may go bad. At lower voltage, the current may be actually higher than 20A (this is clearly not a pure resistive load).

Nothing appears to be visibly damaged; just try to plug it once more. I hope your power supply can deliver 1KW at 30V (your power supply may die).

I got it working. I totally missed that the copper heating tube coil was squeezed together and current didn't go whole tube length instead jump through whole coil as there is no non-conductive coating on it.

If it is a tube, you are supposed to pass some coolant through it so that the copper tube does not get hot unnecessarily. If 1000W is delivered to a load in a small volume, the temperature will be high enough to melt a piece of iron. Part of this heat will be reflected onto the copper coil. Does it work for other metals besides iron? I am just curious.

Yes, I know, I bought small water pump as well. To be honest, I bought it for brass annealing. Well, I tested it and it is next to useless for brass. It heats it but is super slow. Perhaps it needs ferrite core which has split on one side and both sides wrapped copper wire to focus the engergy to small spot...