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Induction Heater project

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mister_rf

Sat Jan 17 2015, 11:34PM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

I've been reading a lot on the subject and I hope that Iâ€™ll have enough time to spend it for, in order to obtain some results until end of this year.

My initial approach is to use the Series Resonant tank via a toroidal coupling transformer.
Similar to other members, thatâ€™s a project only for fun, so there are no imposed requirements for now on.
End of the test I hope to achieve up to 3KW (maximum safe power using the standard 230Vac outlet).

For the tank capacitor I use three Inductotherm 670nF capacitors (thank you again Wolfram for the tip about cheap induction heating capacitors on sale).
As a result the working frequencies will be around 70KHz - 100KHz.

I have in plan to start my first experiments using a low voltage and various MOSFET/IGBT's and based on the learning curve to finish this project using two SEMIKRON SKM400GB125D IGBT modules.

First, I have done mechanical engineering works. Here are some pics.

Gathering all the necessary elements:

Preparing tank cooling pipes and mounting the caps:

Assembling the coupling transformer (20:1). Mounted the working coil:

Rectifier/filter caps/IGBT modules:

loneoceans

Sun Jan 18 2015, 01:33AM

Registered Member #4098 Joined: Fri Sept 16 2011, 09:26PM
Location:
Posts: 236

Hey that looks like a fantastic build. Very clean and you can definitely see the amount of work put into it. Looking forward to the build as it progresses :)

Wolfram

Sun Jan 18 2015, 12:12PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Nice and solid build. It should be able to handle 3kW without any problem.

The High Energy Corp engineer I talked with said the caps should be able to handle 650V and at least 600A. I'd limit the cap voltage to 600V RMS for some safety margin. The total capacitance of your bank is 2 ÂµF, so the tank impedance at 100 kHz is 0.8 ohms (and 1.14 ohms at 70 kHz). This means the tank current will be 600 V / 0.8 ohms = 750 A with 600 V across the caps, leading to a total tank reactive power of 450 kVAR.

If you drive the bridge from unsmoothed rectified mains, you'll lose some tank kVAR. The capacitor voltage in this case is a sine modulated by a sine, which has a peak to RMS ratio of 2, but you're still not allowed to exceed the peak voltage of the capacitor even momentarily. The peak voltage the cap is rated to handle is 600 V * sqrt(2) = 850 V, so the maximum RMS voltage you can safely apply in this case is 425 V. With the tank impedance being 0.8 ohms at 100 kHz, you'll get a tank current of 530 A RMS. At 70 kHz (1.14 ohms) you will have a maximum tank current of 370 A RMS, with a max reactive power of 225 kVAR at 100 kHz and 160 kVAR at 70 kHz. With reasonable coupling to the work you should still be able to achieve 3kW of power transfer to your workpiece.

With your 20:1 coupling transformer, primary currents will be maximum 25 A, so I think the 400 A semikron bricks will be a bit overkill. Smaller IGBTs will have lower switching losses than the big bricks, so I would go with some of those instead.

If you go for a higher operating frequency, you should be able to provide more reactive power even with just a single cap. I would guess around 5 kW or more with one cap, running at 200 - 250 kHz. Of course the driver design would be more challenging in this case.

mister_rf

Wed Jan 21 2015, 11:40PM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

First of all, thank you for your advice and guidance.
Yes, thatâ€™s true; I have the same feeling that using the SEMIKRON bricks is far more than is needed for the actual setup.

Anyway, I have in my plan to test various transistors for this experiment, as my personal collection of transistors grew up in time, and maybe later on, those will be used for a final upgrade.

Experimentonomen

Sat Jan 31 2015, 12:51PM

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

You should flatten the copper pipes alittle to get better thermal and electrical contact with the copper strips mounting to the caps.

Josh Campbell

Fri Feb 06 2015, 12:18AM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

Great job on the initial tank setup, you should have no problem keeping it all cool.

One thing you will notice is that due to the large amount of stray inductance in that type of tank setup, it will heat up any metal (such as a case or parts on a nearby control board) that comes with a few inches when running at moderate power levels. But like you said this is just for fun/learning so you'll probably end up just mounting the thing on a board, which has the added benefit of keeping everything open for easy access.

When you get to the point where your are using your IGBT bricks there is nothing wrong with using good GDT's to drive them. However I would suggest using a hybrid driver not only to give yourself greater flexibility (on-time, dead-time, phasing, etc) but also to protect your investment (good bricks aren't cheap). If you read about series resonant tank setups in induction heating you will find a number of issues involving bridge protection.

Hybrid Driver Example

mister_rf

Tue Feb 10 2015, 11:58PM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

Thanks for the tips. Over the past few years I have done some research and a lot of reading on this subject and now I have prepared elements for testing hybrid gate drive prototypes. By the way, you're one of the people whose hard work and detailed experiments in this area leads me to start such a project. Thank you again.

For example I have considered to test the HCPL316J gate drive optocoupler, M57962L / VLA542-01R and based on Wolframâ€™s project, the Silabs SI8234/SI8244 drivers.

(@Wolfram, Iâ€™m still sneak a peek on your experiments, see the cloned auto-range frequency meters prepared for

)

Gabriel35

Wed Mar 04 2015, 05:19PM

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

Hello! Where I can find those capacitors for sale? I need them to build my version of a Induction Heater too...

Thank you!

mister_rf

Wed Mar 04 2015, 10:24PM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

I was lucky.

I have purchased those caps on eBay thanks to the info shared here by Wolfram, see details here:

Gabriel35

Thu Mar 05 2015, 03:05AM

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

The listing is ended, what a pitty...

If some of you guys know about any other capacitors like HEC, Inductotherm, Eurofarad or even CELEM at good price and available for sale, please let me know.

And congratulations for the project, i'm looking forward to see the progress, it promises to be very tough IH experiment.

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