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Half Bridge MOSFET Induction Heater Problems

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LAN_403

teravolt

Sat Sept 05 2009, 02:17AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I think your circuit might work, try the schematic on a proto bord if pausible. The device has a little delay in it. I also think that you could dump all the zeners if you are using a regulated supply

Gabriel35

Sat Sept 05 2009, 04:02AM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

OK! i've mounted it on a PCB,
I'm afraid of killing this IR2184 Driver,(Yes they're expensive) because of that i've asked if the conections were right...
So it means that the design that Karim Ladha drawed is just for reference, the right conections are like i've drawed, alright?
Can I turn just the driver part of the circuit on first, and then the Inverter part? or it can damage something?

Thank you!

uzzors2k

Sat Sept 05 2009, 10:54AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I see several mistakes. For one thing, remove the 10k resistors from the input and Vcc pins. "In" is a high impedance input, and Vcc needs access to the full 15V without severe current limiting. Also you've got 15V going into COM or the "common ground". Go through the datasheet again and look at page 5, you seem to have mixed up the pin functions and numbers. Kim has them ordered correctly in his schematic, so just use it for reference.

About the matching inductor, it's two windings on one core, though the schematic says one winding can also be used.

Gabriel35

Sat Sept 05 2009, 02:01PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

Oh! yes you are clearly right!
now i've saw the page 5. Kim's drawing is perfectly right...
I'll make the changes

Thank you!

Gabriel35

Tue Sept 08 2009, 12:46AM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

Hi all!
i got some photos of the work...
I need someone to say if the Current transformer and the "Air cored inductor" are right
And the other photos are just for showing the work:

the last one is a IGBT that i've got, rated 1200v and 35A, fullbridge of 6 "mosfets" with built-in free-wheeling diodes

so if I don't have sucess with the IRFP's i'll try this IGBT,
and for the tank capacitors i'll buy 14x 220nF - 1000v capacitors, (the ones on the photos are just for testing purposes)
what do you think?

Thank you!

uzzors2k

Tue Sept 08 2009, 01:31PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Looks good, just using thicker insulation on the current transformer's primary to avoid arc-over.

Gabriel35

Tue Sept 08 2009, 05:06PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

I've finally turned the heater up...
I got a little "bzz" noise when i put the potentiometer all the way right, it varies from 0.00A to 3,16A (the thing is oscilating)
When I put the potentiometer is all the way right and it gives me 3,16A(pretty low) and the mosfets, the coil and the tank caps warm a little..
The screw (on the work coil) starts to heat a little too

So it seems to be working, but the amperage is still low, (~3,0A) (i'm using 41,2VDC)
Something is limiting the current too much...

Another thing that i've found strange is that, when I turn the potentiometer all the way right and there's no workpiece on the workcoil the amperage is 3,16A and when i put a screw on the work coil it falls to 2,64A
I've noticed that when I tried to turn the inverter part with 36vDC the amperage stayed at 0,00A turning the potentiometer,
so maybe is just a voltage problem, perhaps it need more voltage to excite well...but i'm afraid of trying it with 250vDC because the mosfets heat pretty well now, maybe with 250vDC they can blow... or not?

Any clues?

Thank you

Steve Conner

Wed Sept 09 2009, 09:32AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

If the max current is at one end, sounds like your pot needs some more range. You should be able to tune through the maximum.

Gabriel35

Wed Sept 09 2009, 03:46PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

current hits the maximum @ about 7/9 of the pot (i've forgot to mention this detail...)
So i think that the pot is fine
I still think that it need more voltage...

What do you think?

teravolt

Thu Sept 10 2009, 03:32AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

have you tried playing with the tank capacitors to increase the circulating current? Tonskulus or anybody does the 100k trimmer change pulse width to the fets

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