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OMG Induction Heater

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Steve Conner

Mon Jan 07 2008, 05:11PM

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

Hi kim_ladha, welcome to the forum! Your induction heater is great, it seems to have inspired everyone, including me

BTW, are you also water cooling the capacitors, or are those heatsinks the only cooling they have?

Experimentonomen

Mon Jan 07 2008, 05:36PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

Here comes the schematic, kim sent it to me via email and granted me access to publish it here.

kim_ladha

Tue Jan 08 2008, 01:52PM

Registered Member #1217 Joined: Mon Jan 07 2008, 11:46AM
Location: Leicester, UK
Posts: 11

Hi Steve,
I use a 0.75 k/w aircooled heatsink (cut in half) for the capacitors. The max dissipation of the capacitors is higher than the heatsinks can handle but it takes 10 minutes or so to reach their max opperating temp of 85C. The water cooling is really just for the work coil- if run with no work piece, the water comes out almost boiling! The heater draws 13 amps at 240v at this condition- thats more than a normal kettle. I guess about 90% of this power is being dissipated in the coil alone, the rest being dissipated in the igbts and capacitor.
Karim

Marko

Tue Jan 08 2008, 02:43PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Awesome to see you here sir! Welcome to forum.
That is one of first heaters I could call *useful*, keep this work up!

One thing I don't understand here is, how are you taking current feedback just like that from the parallel LC tank?

Steve Ward had a hard time assuring me that that is impossible, as matching inductor would be hard switched with rather poor power factor and result in gross overheating of IGBT's.

Also, thinking abut water cooling, does the conductivity of water ever represent a problem?
You are running it through quite high potential gradients. Distilled water can acquire rubbish through time which makes it more and more conductive.

Radiators and pumps, you keep them just grounded?

Any plans on upgrading the water cooling to cool the caps and maybe switches?

Marko

kim_ladha

Wed Jan 09 2008, 11:54PM

Registered Member #1217 Joined: Mon Jan 07 2008, 11:46AM
Location: Leicester, UK
Posts: 11

Wow, lots of questions....
The feedback is definitly only possible from the actual tank circuit and only for inductor fed resonant tanks. I have 800 amps going through mine so it is hard to just use conventional techniques. To drop the current i put a loop of coax braid (any copper wire will do) soldered on one of the straight sections of the work coil. The connections are 1" appart and this 'resistivly' drops the current to 50 amps or so- this is simply due to the resistance of the copper pipe! Then i tried several closed ferrites but they all over heated. Finally I used a c core, the air gap stops saturation and it kept cool. This went into a 1:500 current xfmr (cheapo plasic type) to get a few milli amps which i use for my pll signal. (using the term pll loosly). I came up with the concept using pspice- the theory is sound and reliable.

As for the other things. 1). Use long plasic water pipes- water conductivity is not really a problem however
2). You can short out the work coil in my design, the current becomes square wave and switching losses are high- it doesn't break however. Same happens if you loose current feedback.
3). Grounding only represents a problem if the circuit fails and your touching the coil/water. I use an isolation transformer for testing so i don't die- no earth. The coil is live but safe to touch probably due to the high frequency. In a normal failure it will also be safe to touch. There is always a chance that the devices will short so that it is connected to live- although unlikely, I try and avoid touching it. For normal heating work you can just connect it straight to the mains- every device failure I have had in any equipment like this ALWAYS blows a fuse and isolates it. Of course- the time it doesn't could be your last so be careful!
4). No plans to upgrade circuit anymore. I am at the limit of what I can draw from a mains plug socket already! If I wanted to make a 5-6 kw version, the fgh50n6s2d looks like a safe bet.
Karim

HV Enthusiast

Thu Jan 10 2008, 01:19PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Actually, there is a VERY NICE High Energy water-cooled induction capacitor on EBAY now. And a good price too.

EBAY ITEM: 280185795601

Experimentonomen

Thu Jan 10 2008, 04:04PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

This capacitor is meant for vacuum tube ih, not solid state. ItÂ´s 2nF @ several kilovolts.

HV Enthusiast

Thu Jan 10 2008, 06:21PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

HFsstc-freak wrote ...

This capacitor is meant for vacuum tube ih, not solid state. ItÂ´s 2nF @ several kilovolts.

you have something against tubes???

Experimentonomen

Thu Jan 10 2008, 08:26PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

Absolutely not, i just thought this thread was for ssih.

HV Enthusiast

Fri Jan 11 2008, 01:26AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

HFsstc-freak wrote ...

Absolutely not, i just thought this thread was for ssih.

No, the subject title that you started is "OMG Induction Heater."
If you wanted to keep it solid state, you should have made that clear in either your first post or through the title.

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