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BSM25GD120DN2E 3224 IGBT IH Working!

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Gabriel35

Sun Sept 13 2009, 07:50PM

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

Hi all!
I'm building the Kim Ladha's induction heater, and i think i got it working, but i still have some doubts
I'm not using Celem Induction Heater capacitors
The IH is already oscilating because the workpiece, workcoil, and tank capacitors are warming a little.
The WorkCoil have 4 turns...
1st- The fets(IRFP's460) heated pretty well with 30~40v @ 5,5A on the inverter part...(shouldn't they work cool?)
2nd- The current kept limited by the Zmatch inductor...does the current rises with more voltage?
3rd-I've noted is that the circuit don't get to oscilate if i use 5,6nF 10nF or 22nF capacitors between current transformer(100:1t aprox.) and workcoil part of the circuit, i just got it to oscilate with a 100nF or higher - 1000v ones, someone knows why? Can this fact be limiting the circuit in something?
Do you think that if i try to run the inverter part with 250vDC the mosfets can blow?

I have some photos of the work below, and the schematic if someone don't remember it:

Schematic idealized by: Karim Ladha

Any Ideas?

GeordieBoy

Sun Sept 13 2009, 08:09PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

You really do need a decent oscilloscope to diagnose what is going on here. In general if something in power electronics isn't working properly at reduced voltage, then it will likely go bang when you turn up the supply voltage. You need to get to the bottom of what's happening before you increase the power.

I'd also recommend you copy someone's design *EXACTLY* if you don't know what you are doing, then you have more chance of it working. Substituting different capacitors and power transistors is only a good idea if you know that these changes won't effect operation.

-Richie,

Gabriel35

Mon Sept 14 2009, 02:14AM

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

Should i have a couple of filter capacitors between rectified mains and inverter?

Hernan

Mon Sept 14 2009, 03:28AM

Registered Member #1614 Joined: Wed Jul 30 2008, 03:08PM
Location: Argentina
Posts: 52

Gabriel, this is the circuit that I use:
It works very well and mosfets stays cool The caps between Drain and source form lossless snubbers and helps to keep Irfp460 cool but only works with inductive load
]ih.zip[/file]

Gabriel35

Mon Sept 14 2009, 03:46PM

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

Thank you for the schematic Hernan, it is a bit more complex that this one that I'm trying, and i think i don't have acess to some parts drawed on it...
If i really can't get nothing from the actual circuit i think I'll give up trying to build this thing...
this os the second circuit that i'm trying and i'm a bit tired already...

The workpiece is warming a lot with about 2 minutes of work (about 120ÂºC), with zmatch limiting the current to 1,5A @ ~34v(mosfets pretty cool)
if i change the zmatch and rise the current to 3,2A the fets get painful to touch with about 30 secs of working
Maybe this circuit is designed for using exclusively with IGBT's?

keeps my questions on the 1st and 3rd comments

Thanks!

Hernan

Mon Sept 14 2009, 11:24PM

Registered Member #1614 Joined: Wed Jul 30 2008, 03:08PM
Location: Argentina
Posts: 52

Yes, I feel very angry I same situations when circuits doesn't works.I want to throw all away by the window.
I recommend to use a variac to slowly raise the voltage checking waveforms with a scope.

regards,
HernÃ¡n

Gabriel35

Tue Sept 15 2009, 01:29AM

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

yes, i feel that way sometimes, but the feeling os victory when everything is working, compensate the wasted time...
I Don't have a variac, how can I obtain one?

teravolt

Tue Sept 15 2009, 03:10AM

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

Gabriel if you want to do it on the cheap you could use a standard 600w light dimmer and a seies resistor (for current limmiting) and a capacitive doubler. I don't know what your buget is like but a good buget oscilloscope say 100MHz would be a must for this type of work

IamSmooth

Tue Sept 15 2009, 03:33AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I got my scope on Ebay a long time ago. There are some good deals depending on when you get one.

Gabriel35

Tue Sept 15 2009, 03:56PM

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

i have a 8800w dimmer based on TIC41 but it don't variates the output of the transformer, i think it just work on resistive circuits , like electric showers

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