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Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
...currently only tested to 4KW because I'm too lazy to plug in the triple variac. Inverter is a full-bridge of CM400DU-12F IGBT's, being driven by a GDT that is being driven by an intermediate H-bridge of HGTG30N60B3D's. Yes, the gate-drive transistors are way overkill but I had them around, and it works, so what the heck! Driver is a simple TL494 oscillator; I never got the PLL working satisfactorily Tank cap is a giant Eurofarad snubber, rated for 500Vrms and 150Arms. Work coil is 4 turns of 1/4" copper tube for a total inductance of somewhere around 3uH. The whole setup resonates at around 65kHz. The coupling transformer is 20:1 wound on four giant toroids from Magnetics, Inc. It draws around 20A unloaded with 200V on the bridge, going down significantly with large ferromagnetic workpieces and slightly with other workpieces. I might have to twiddle the ratio to get the right current at 300V (I'm aiming for 40-50A on the final version). Bridge and secondary are all water-cooled. The limiting factor right now, I think, is the tank cap. This one should be good to at least 10KW, but I'll be needing more snubbers in parallel if I ever want to go to higher powers. No pictures of it running yet because (1) I forgot and (2) no one really wants to see *another* red bolt. It'll melt aluminum right now, but aluminum doesn't glow pretty colors. I'll post a video or something when I do the 3-phase run. Yes, I know using a steel case is bad, but the case doesn't get too hot, so it should be fine.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
"Only" 4KW???!!! That's about 10 times the size of the induction heater that I was thinking of building. Will you be using it for "industrial" processing, or is this just a big "hobby" project?
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I have mine all set and ready to run, and it has two of those caps, and PLL. I'm just afraid to plug the damn thing in...Water cooling, but instead of copper busbars I've got aluminum ones.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Xray wrote ...
"Only" 4KW???!!! That's about 10 times the size of the induction heater that I was thinking of building. Will you be using it for "industrial" processing, or is this just a big "hobby" project?
BTW - NICE JOB!
I say "only" because the bridge is good for *a lot* more; at the currents I'm running it at right now I could just as easily use the transistors in my gate drive It's a hobby project, mainly because my new obsession is high current. The fact that it's useful is a nice side-effect.
Inducktion wrote ...
I have mine all set and ready to run, and it has two of those caps, and PLL. I'm just afraid to plug the damn thing in...Water cooling, but instead of copper busbars I've got aluminum ones.
I'll fool around with it soon enough.
Go go go plug it in! Are you using bricks? If so, its unlikely to blow up unless you are doing something utterly retarded (e.g. phasing gate drive wrong and shorting the bridge). I once screwed up the gate drive on this thing and caused the inverter to dissipate 400W, and nothing happened (well, the bricks got hot, but not quite to the point where they released their magic smoke).
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Bwang -
Very nice! Looks like the tank should be able to handle much higher power levels.
A few questions: What's the value of your tank cap? Do you know what type of ferrite material you used in your coupling transformer? Do you see much heating of the ferrite itself over a few minutes of run time?
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
The tank cap is 3.75uF, ferrite is the 5000u Magnetics material. The cores don't heat up appreciably, though the 10AWG wire on the primary gets a wee bit warm.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
bwang wrote ...
Xray wrote ...
"Only" 4KW???!!! That's about 10 times the size of the induction heater that I was thinking of building. Will you be using it for "industrial" processing, or is this just a big "hobby" project?
BTW - NICE JOB!
I say "only" because the bridge is good for *a lot* more; at the currents I'm running it at right now I could just as easily use the transistors in my gate drive It's a hobby project, mainly because my new obsession is high current. The fact that it's useful is a nice side-effect.
Inducktion wrote ...
I have mine all set and ready to run, and it has two of those caps, and PLL. I'm just afraid to plug the damn thing in...Water cooling, but instead of copper busbars I've got aluminum ones.
I'll fool around with it soon enough.
Go go go plug it in! Are you using bricks? If so, its unlikely to blow up unless you are doing something utterly retarded (e.g. phasing gate drive wrong and shorting the bridge). I once screwed up the gate drive on this thing and caused the inverter to dissipate 400W, and nothing happened (well, the bricks got hot, but not quite to the point where they released their magic smoke).
I'm not using bricks, I'm using TO-264 500 v 100 amp fets from fairchild, on a rather hefty aluminum heatsink.
EDIT;;;
Success! It works without current limiting! I can use the inductor (since I'm running parallel resonance, not series yet) as a sort of variable resistor. Move core out, more voltage + current, move cores closer, less current and resistance due to increased inductance. Yay.
Also, I apologize if this ends up hijacking your thread... I'll move to my own once I get the water cooling up and running (right now it's sort of leaky, and my parents + leaky + electricity = a no no)
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Big Induction Heater
