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Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
Answers: 1: Seems to be ok. btw are you sure that ct has correct phasing? Try swapping secondary winding other way around. 2: - 3: Current is limited by Zmatch. There is no "right current" for fixed voltage. Lowering Zmatch impedance rises input current and vice versa. Mosfets will heat a littlebit anyway but it can be minimized after some finetuning. 4: Depends on Zmatch impedance and load. 0.1-1000A. My induction heater takes 20Amps (unloaded workcoil) using 17µH Zmatch coil. Current may drop down to 3A if heavy enough workpiece is to be heated. 5: no idea
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
1- i'm not sure, what i can say is that, ive tried different CT's , one of them was 40:2, and seems to work almost equal, but i can try some modifications on it... when I bypass the capacitor that goes on the CT's leg with a piece of wire it takes more amperage... and when i disconnect the CT from trigger, it don't even oscilate, i get 0.00A. 5- do you need to start it @ low voltage and then rise it up , or if you start it with 220v it already works?
Thank you again Toni, your answers always give me some uplift to continue the project..
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
hey i was wondering: don't you think that the 5th problem is related to the internal diode of the IRFP460? what about i'm trying to bypass it with some ultra-fast ones?
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
It can be started at full voltage. I have only two choises, switch for 115V or 230V. So i can choose low power or full power. And another switch is for driver circuit.
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Hi all! I think I'll give up MOSFETS, and try some IGBT's now maybe the problem can be solved with this change... i have one BSM25GD120DN2E 3224 IGBT Module with 6 IGBT's Inside... The Datasheet is here:
So what do you think about this module? Do you think that i can achieve some regular power with it? what abou thge frequency?
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
hey! I got everything working here!!! i've got the big BSM25GD120DN2E 3224 IGBT Module to work and it works really NICE! Now i'm sure that the problem of the previous version was the IRFP's460, they heated a lot and the current on the inverter part was very limited. Now, how i turn the potentiometer the amperage goes up, but with 10k pot I was just able to reach 5A ad the sistem was not ressonant yet, so i've changed the potentimeter by a 50K one, i've noted that it reaches ressonance with about 18K Ohm @ about 7A (41v), I got a little test to do, one time that i still don't have a osciloscope... I got my cellphone near the work coil recording it with the video camera, it's really nice to see, when it hits the ressonance point the cel phone get a really dirty interference, that shows up suddenly, and if i keep rising the potentiometer the amperage starts to fall... So now what do you think? it's working like it should work huh? I just need to get some bigger dissipators for the IGBT module... I'll post some photos soon
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Don't worry It's just near the work coil... the IGBT is perfect, and the driver circuit too.. but i'm not sure about the Current transformer and the workcoil/capacitors because the IGBT is still heating pretty well (all this trying the circuit with 41,2vDC) do you think that it's because it's still badtuned? I've found something very strange, first i was using 10k pot, it asked for more range, i've chaged it for a 50K one, and it was still needing more range. finally i chaged for a 100k one, and the question keeps on my mind "maybe i need more range than 100k?" how i was changing the potentiometers the amperage always get higher, i started limited to 5A with 10k, 6,9A with 50k and now 9.00A with 100k... when i turn the potentiometer the HUMMM noises get higher when it's near the end... Does the IGBT needs to run on skin temperature or very hot? Does this circuit works with 9x 330nF tank capacitors or it JUST work with those CELEM caps? the Coil has 4 turns. is it right? I need to buy a decent Amp meter now, because i've melted my multimeter wires with 9A... Do you think that i'll just find theese answers only when i get a osciloscope?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
I was thinking that you could make your own current probe with toride and a LED or lamp and some resistors. Insert one end of the work coil through the toride. As the work coil becomes resonant the current will go up and you will be able to see it. The transistors should not do a lot of work and or get hot. Current will be traped in the work coil and cap. what do you think?
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
toride? do you mean "Triode"? do you have any other specification on some values of the components that i should use to do this? the higher is the current flowing through the work coil, higher is the temperature that the workpiece can be heated? and when it hits ressonance the led glows more? Thanks!
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BSM25GD120DN2E 3224 IGBT IH Working!
