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induction cook-top driver uses

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brandon3055

Mon May 14 2012, 06:29AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Hi all this is my first post here so please tell me if I mess anything up.
I have recently come across the power electronics out of an induction cook-top (not working) and I was wondering if any of the parts could be used to build an induction heater. I haven't had a chance to test the IGBT's (gt60j323) yet but the caps should be fine there are two .65uf and two .76uf 800v 50KHz.
Ons a related note I have recently tried to build a royer induction heater from the omg induction heater thread but I keep blowing mosfets I think its because I'm using 15v zener diodes but i just wanted to find out before I blow any more mosfets (irfp250)
Thanks

Ben Solon

Mon May 14 2012, 11:58AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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Posts: 600

The zvs driver works with no gate protection at all. In a version i recently built, it uses two 30n60 igbts and two strings of two 5819 diodes. While it has the potential to destroy the thing, it really shouldnt unless you run greater than 15v(20v pulsed) through the gates. I could heat small objects to 800C(1450F) from 12v @ 4-6A. And with those parts, you could definitely build something similar to the "omg heater" as long as those caps can handle it. In the thread, he uses many mkp caps and they still where heating badly.

brandon3055

Mon May 14 2012, 01:00PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

[quote]
The zvs driver works with no gate protection at all. In a version i recently built, it uses two 30n60 igbts and two strings of two 5819 diodes. While it has the potential to destroy the thing, it really shouldnt unless you run greater than 15v(20v pulsed) through the gates. I could heat small objects to 800C(1450F) from 12v @ 4-6A. And with those parts, you could definitely build something similar to the "omg heater" as long as those caps can handle it. In the thread, he uses many mkp caps and they still where heating badly.
[/12quote1336999725]

Hi ben123324
Thanks for the advice I will definitely give if a go if the igbt's are ok (do you mean 1n5819 what were that used for ?)
I have never used igbt's before so any advice would be welcome.

I should have time to work on it this weekend I will se what I can come up with

Ben Solon

Mon May 14 2012, 02:37PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

you would be better off with some mosfets like the irfp250/260 because igbts may not drop the same voltage causing asymetry in the circuit. the only advantage of igbts in a mazilli circuit is the losses are caused by switching rather than conduction: at lower frequencies the losses are lower.

the diode strings are two 1n5819 diodes in series. there are two these strings, each going from one devices gate to the other devices drain/collector. any diode works if it is fast and has decent current handling. should also stand off greater than pi*supply voltage.

i would post a picture from my zvs setup, but ipods dont support attachments... but i had ~2.25uF capacitance and 3+3 turns and 7+7 turns of thick magnet wire coils that i could change out.
edit: here you go-

i would be happy to helps answer any questions you have

and if i cant, than plenty of the people here who could will.

if you are interested, i am building a BIG lclr parallel resonant heater up to 4kW on my website:

i dont updated it as much as i should though.

anyways, welcome to the forum, and good luck!

brandon3055

Mon May 14 2012, 10:27PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Thanks for the pics I will post some of my setup ASAP I'm running a bit low on 250's at the moment but i have got a ton of irfp460 for my Sstc would they work for a higher voltage lower current version ?

Ben Solon

Mon May 14 2012, 10:59PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

yep, the only real difference is the on resistance and voltage. But don't put much more than 36v in unless you know exactly what king of power to expect. 12-24 is well enough for a low power version. mine was ~70W running off of 12v, and the breadboard was the limiting factor. the more voltage, the higher power fets you need.

brandon3055

Mon May 14 2012, 11:40PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Dosent decreasing the capacitor value decrease the current draw ?

Ben Solon

Tue May 15 2012, 12:19AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

sort of, but generally you want more capacitance. the more capacitance, the higher the potential current in the lcr tank. the higher the input voltage, the higher the actual current in the tank. so basically if you put 36v into the driver with a .1uF tank cap, you cant achieve the resonant current you want because the capacitor "fills up".

I=C(dv/dt) shows this. for the same dv/dt, the current will be larger with larger capacitance. the frequency also effects current, obviously because voltage is changing faster. this is something that i know, but that i cant explain very well(i may have confused myself more than anyone else by typing this) so if anyone else watching this thread wants to add, please do so!

brandon3055

Tue May 15 2012, 12:33AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

I wonder how they overcome that problem in comercial appliances
(haven't had a good look yet but i think the board I have uses push-pull)

Edit: tonight I tried my old design with the 10v zener diodes and it works grate but i can't post images in a reply. Also about that driver board the igbt's work fine and it terns out those caps are just part of the push-pull setup the tank cap must be a part of the hot-plate

Ben Solon

Tue May 15 2012, 02:25PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

It makes sense. I never knew how they sit up the induction cooktops. With the cap in the coil there is a smaller resistance loss between the coil and the cap. The only problem I see is they now have to keep the cap cool while it's touching a coil that may heat up.

The mazilli driver is a push pull after all. Just a self oscillating resonant one. And in industrial aplications they generally use lower frequencies. That way they can more efficiently heat larger objects. But one of the purposes of hf ih's are for heating of microtechnology. Ever wonder how they solder/join the points in ic chips? I have a video of an EEPROM ic chip under magnification on a microscope and you can see wires many times smaller than human hair soldered to pads.

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