30 KVA Induction Heater

507,505

724

281

Introduction: 30 KVA Induction Heater

Introduction

Induction heaters are used to heat conductive materials in a non-contact process. Commercially, they are used for heat treating, brazing, soldering, etc., as well as to melt and forge iron, steel, and aluminum.
This Instructable will walk you through the construction of a high-power (30kVA) heater, suitable for melting aluminum and steel. Note that to take full advantage of this design, you will need a 220V outlet, at least a 50A single-phase one and preferably a 50A or 60A 3-phase outlet.

About the author:

Bayley Wang (me) is a EE student at MIT. I'm responsible for a variety of nefarious power electronics projects which you can find on my blog; perhaps most interestingly is oneTesla, which has since gained a life of its own as a startup creating DRSSTC kits.


WARNINGS

  • This project uses mains voltage. While well-behaved, 110/220 mains can seriously injure, maim, and/or kill you if used improperly.
  • The voltage across the tank capacitor can potentially ring up to hundreds of volts. Don't let the 20:1 step-down ratio fool you!
  • When scoping the circuit, beware of ground loops.
  • The work piece, naturally, can get very hot. DO NOT TOUCH! Less obviously, do not rapidly quench the work piece with water, as this can lead to dangerous sputtering.
  • This project uses power electronics. Under fault conditions, semiconductor devices used in this project may rapidly heat, vent, and/or release rapidly moving shrapnel. Shield appropriately.

WIth that said and done, let us move on.

Step 1: Bill of Materials

For this build, you will need:
  • 2 IGBT half-bridge modules. I used Powerex CM400DU-12F 400A 600V Dual IGBTs; anything of similar power handling and switching speed should work. These can be purchased as cheap surplus from Ebay.
  • 4 MOSFETs or IGBTs for the gate drive. I used HGTG30N60B3D's, which are way overkill for the application. They need to be able to dissipate about 30W without burning up.
  • 2 gate drive IC's, of at least 9A peak current capability. I use the UCC37322 from TI.
  • 2 ferrite toroids. These are your gate drive transformers, and should be able to pass a reasonably clean square wave at 50 kHz. Magnetics, Inc. and TSC Ferrite International are good manufacturers, or you can salvage them from old CRTs or switching power supplies. The powered iron cores from ATX supplies rarely work.
  • Large ferrite toroids for the toroidial coupling transfromer.
  • 1 TL494 PWM IC.
  • 1 at least 20 uF, at least 20V film or ceramic capacitor.
  • Assorted resistors, capacitors, and potentiometers for the driver.
  • 10' of 1/4" soft copper refrigeration tubing.
  • A water block capable of accommodating the two IGBTs. A large heatsink may also work, but I haven't tried.
  • 2 aluminum or copper bars, ~3/4"x8"
  • 2 1/4" compression unions
  • A 4-position rotary contactor, good for several tens of amps.
  • A screw-terminal electrolytic capacitor of reasonable quality. I recommend at least a few hundred uF for 3-phase operation.
  • A high-quality, low inductance snubber capacitor for the bridge. Ebay has cute brick-mount 20 uF blocks for $5.
  • One or more high-quality polypropylene capacitors for the tank capacitor. More on this part later.
  • An analog current meter good for several tens of amps.
  • A 3-phase bridge rectifier (or single-phase if you are willing to settle for single-phase operation only).
  • A suitable project case and associated hardware (3-phase breaker, cord, plug, etc).
  • A water pump capable of a couple GPM
  • Tubing appropriate for hooking up the water-cooling.
  • A Variac for testing.

Step 2: Words of Wisdom

The IGBTs: or "bricks", as we like to call them. They should be good for 600V (not a concern, I've never seen a brick rated under that before), at least 200A (I use 400A modules to be, safe), and more importantly, need to be fast. This is where you need to check the datasheet - IGBTs have an inherently long turn-off delay. For 65 kHz operation, rise time + turn-on delay + turn-off delay + fall time should be under 2 uS.
Bricks come in several types: single-transistor, dual transistor, 6-pack, and some rarer types such as chopper modules. Single-transistor modules are prevalent for 1200V and larger IGBTs, and have the highest thermal ratings and are the most difficult to mount. Duals (half-bridge modules) are the much easier to mount and can dissipate less. They are most common for 600V modules. 6-packs are used for 3-phase inverters, require no external power connections, and have the lowest thermal ratings.
Use what you see fit; this tutorial uses half-bridge modules.

The tank capacitor: is very very important. It handles tremendous amounts of reactive power at very high frequencies. It is absolutely essential that this part be selected appropriately. It must be a high-quality polypropylene or mica capacitor. I use giant snubber capacitors made by Eurofarad; alternatively, a series/parallel array of smaller capacitors (such as the Tesla coiler's beloved CDE942 series) should work. The ultimate capacitor, of course, is a water or conduction-cooled unit made by Celem, but such caps will run you about $150 for a 2 uF unit. You want enough capacitance to resonate with your work coil at no more than 70 kHz.

Step 3: Principle of Operation

Induction heaters function by surrounding the work piece with a coil carrying a high-frequency (kHz to low MHz) alternating current. This induces eddy currents in the work piece, which acts as a shorted 1-turn transformer secondary. The currents can be tremendous, on the order of several thousands of amps. This causes high I^2R losses in the work piece, heating it.

Schematic Description
Note:
Ignore the transistor model numbers; I just used what Eagle had built in.

IC1 is a TL494 acting as an oscillator with adjustable dead time and frequency. The output is fed into the input of two UCC37322 9A gate drive ICs, which "beef up" the signal into something capable of driving high-capacitance transistor gates. The output signal is passed through C5 to insure only the AC component reaches GDT1, a gate drive transformer. This transformer provides the electrical isolation necessary to drive Q1 through Q4, which form a full-bridge. This intermediate bridge is necessary to provide the high average power necessary to drive Q5 through Q8, a full-bridge of large IGBT modules.
This bridge forms the main inverter. The output of this inverter is stepped down through a 20:1 torodial transformer TR_MATCH, which provides impedance matching as well as isolation for L_WORK, the work coil inductor. The capacitor C_TANK forms a resonant LC circuit with L_WORK; when driven at resonance, this circuit displays zero reactive impedance to the inverter, allowing for higher powers and minimizing switching losses in the inverter.

Step 4: Construction: Controller

Construct the logic circuit as you wish, either by using the attached images to make boards or using perfboard or a breadboard.
The gate drive transformers must be able to pass a high-quality square wave at your operating frequency. To check this, wind 10+10 turns on the toroid, connect one set of windings to a signal generator, and scope across the other. The output should look like a reasonable square wave.
The GDT should be wound with 5 twisted wires to minimize leakage inductance. Many people have had luck with using CAT5 cable, which comes pre-twisted.

Step 5: The Inverter

The inverter should be very well-cooled, either with a large heatsink or a waterblock. I used a waterblock for compactness and robustness; but a big (think 12"x12"x3" with several hundred CFM of forced-air cooling) should work too. The pump should be relatively large to handle the pressure drop through the work coil (mine was rated for 2GPM).
The main filtering capacitors should be placed close to the bridge itself, preferably bolted across the busbars. You should also use a snubber capacitor (the black box in the picture) placed directly across the transistors to reduce voltage spikes caused by excitation of the parasitic inductances in the inverter layout.
Using half-bridge or six-pack modules is the easiest way to buld the inverter; a bridge of single transistors will require access to a machine shop to do right.

Step 6: Work Coil/Tank Circuit

The coupling transformer should be toroidal. Wind ~20t around some large ferrite cores (I was using a stack of 4 ~4"x1" cores).
The tank capacitor willget warm. It should have significant terminal area to conduct both heat and thousands of amps. If you are using a MMC of small capacitors, solder them individually to large copper plates. If you are using a Celem or a giant snubber, bolt large copper plates to the terminals. Then in either case, solder the terminals to the copper tubing that forms the rest of the tank circuit.
Attach the work coil to the tank circuit using compression fittings; this allows you to change work coils to accommodate different loads.
Make the work coil out of at least 1/4" copper tubing. Thicker tubing is less lossy, but harder to handle; trade-off between the two as you see fit. When winding the work coil, it helps to fill it with sand to prevent the tubing from collapsing. As a rule of thumb, the resistance of 1' diameter copper tubing at 65 KHz is 0.8 mΩ/m; that is, to compute the resistance of your secondary, multiply 0.8 mΩ by its length and divide by its diameter in inches.

Step 7: Testing and Usage

Assemble everything according to the schematic. Use a current transformer on the primary side (100t burdened with a couple ohms around a ferrite toroid will do) to monitor the waveforms.
Using a current-limited bench supply (preferably 30V, 10A), slowly ramp up the voltage until enough current is drawn to give a clear reading on the 'scope. Adjust the frequency pot until the waveform is a clean sinewave, and current draw is maximized (you may have to search a little to avoid harmonics). If you don't have a scope, just tune until current is maximized (mine drew something like 40A at 200VDC on the bus, unloaded).
With ~30V on the bus, load the work coil with a bolt. At a few hundred watts in, it should get hot within a couple minutes. If it draws power, but the workpiece doesn't get hot, check the transistors for heating. If they get excessively hot, your bridge is shooting through.
If all is well at low powers, you are ready for a high-power test. Use your favorite DC source (single phase, three-phase, smoothed, unsmoothed, etc - it doesn't really matter) to power the bridge. Preferably, use a Variac, in case it draws too much current (you can predict current draw from the low-power tests by noting that the heater is a fairly linear load). Don't forget water cooling!
At a few kilowatts, without a crucible, you can melt aluminum and copper and make steel orange-hot. 10 KW+ (50A dryer/stove line or 3-phase) is necessary to melt steel in open air. A crucible helps a lot.
You can control power by very slightly detuning the inverter, or by changing the bus voltage, or by tapping the matching transformer. The latter is a recommended feature, and steel and copper have very different effective "resistances".
Good luck, and have fun!

Step 8: Sources for Components

By popular demand, I've added this page.

For the power components, one word - EBAY.
EBAY EBAY EBAY. There is no way this project could have been remotely affordable without it. For the IGBT's, the most reliable source is CTR Surplus, who goes by the usernames ctr_surplus, deals_ctrsurplus, and lisa_ctrsurplus. CTR Surplus also has a constant supply of large electrolytic capacitors, snubbers, and heatsinks used in this project.
The capacitors are also from CTR Surplus - a search for "Eurofarad" works wonders.
Copper tubing is best purchased from Home Depot (assuming you live in the US). They have prices that beat most Internet sources.
The toroids can be from Magnetics, Inc or TSC Ferrite International.
Miscellaneous small components can be purchased from Digi-key.
Arrow has very good prices on transistors, far lower than most other suppliers.

Submitted by MITERS for the Instructables Sponsorship Program


EXTREME! Challenge

Finalist in the
EXTREME! Challenge

1 Person Made This Project!

Recommendations

  • Make it Glow Contest

    Make it Glow Contest
  • First Time Author Contest

    First Time Author Contest
  • PCB Challenge

    PCB Challenge

281 Discussions

0
MarkO170
MarkO170

1 year ago

I built a heater based on this circuit. I used the same IGBT bricks as the author and the same basic architecture - low power oscillator section driving a transformer in turn driving an intermediate stage which then drives another transformer to drive the bricks.

I have to commend the author for putting this here.

I don't have access to 3 phase power - and am using a 30 amp dryer (single phase 240 volt) outlet.
I'd like to pass along some things I found out along the way.

These IGBT bricks require a lot of drive and it surprised my how careful
I had to be with the driving stage. I went through several iterations
of this before I got a circuit that didn't cause ringing on the IGBT
bricks or burn itself up trying to drive them. There were very high
current pulses being drawn from the 15 volt power supply, causing failures in - think catching fire/exploding - smoothing caps. Adding series
gate resistors for the IGBT brick gates (3.6 ohm/5w) helped as well as
using a 20uf poly cap across the rails.

If your tank circuit has high Q it can ring up to a voltage that might astound you. I've seen more than 500 volts across the tank capacitor. And it's difficult - i.e. expensive - to find capacitors that can handle this voltage without becoming damaged. Once there's a load in the work coil the voltage drops but it still can be several hundred volts. Choose your tank capacitor wisely!
I used one of the LC4 series made by Illinois Capacitor which are conduction cooled caps made for this purpose.
The turn-to-turn voltage across the work coil can also be high and the hazard of either contacting it - and getting a potent shock, which I can attest to - or the workpiece causing a short by contacting it is present. I got some ceramic sleeving from McMaster-Carr which I put over the work coil tubing that mitigates this danger.

I get about 4KW being consumed which is close to the max for a 30 amp circuit. 6-8KW might be possible for a 50amp circuit. By far the biggest heat producer is the work coil. Even with 3/8 tubing it generates a lot of heat and water cooling is a must. I haven't found that the IGBT bricks generate much heat at all, at this power level they're loafing.

You must also consider the ESR of your main filter cap. Even with a snubber across the power rails at the IGBT bricks it's still going to see a fair amount of current. Don't use a cheap cap here, you might get a hot capacitor or worse a spectacular failure. Better yet parallel two or more. Before doing long runs with it make sure your caps aren't heating up excessively.

Also the power factor of this circuit is not good. You can improve it by putting an inductor in series with the mains going into the rectifier. I used a 1.7uh inductor - all I had room for - and my power factor running at 3.5KW is about 66%. Others may have better ideas on how to improve this, but if you want to run at truly high power levels it needs to be addressed.

All in all a fun project and I learned a lot - and am still learning - along the way!

0
REDMACHINE-A
REDMACHINE-A

Reply 2 months ago

Hi Mark,

Is possible to you contact me to my e-mail adress? I would like your best help about this project.

My e-mail: paulo.carvalho@millenniumbcp.pt

Thank you and best regards,
Paulo

0
REDMACHINE-A
REDMACHINE-A

Reply 6 months ago

Hi Mark,


I am
Portuguese guy and i have built (almost) this induction machine with aim to
melt a small amount of inconel steel. At the present i have all machine build
with coil tank ready, inverter ready, cooling system ready. But as i am not too
much intended about electronics i asked help to a near friend to build
electronic drivers from Bwang instructions sheet. I already have 2 boards ready
to use. My problem at the moment is to build those toroids on pictures. After
read and read and read again Bwang instructions i can't get those toroids ready
to use. I don't understand how to get the square wave they should have. Instructions sheet are
not too much clear and also not too much detailed to a common person like me.
Also pictures are very poor on details and some are blur... I talk with my
friend about this project but he also can't help too much. You can't image how
many people here and at youtube and in my country i already asked help, but it
seems no one understand this kind of electronics, or don't have time to help.
And a few some, who could help in my country... welll very expensive to my
pocket!


So, i would
like to ask you if you could give me some support to finish, test and run my
induction heater. For now i would like some comments about those toroids,
specially how to get that square wave with good quality. Some
pictures could help a lot! I also read attentively your post about this
machine. Could you please sent me some pictures showing how did you connect
resistors series at IGBT bricks gates?


If you can
help me please sent your help and pictures to my job mail where i have full
time access (except weekend): paulo.carvalho@millenniumbcp.pt
(my private one is: vfr998@gmail.com), or
you can sent to both boxes, no problem.





I am also
pretending to buy a VARIAC to test machine, but i saw several kinds of variac
power... so... which one to buy?? I need input 220v 50 Hz, but what kind of
output power is needed to test this machine? 500 KVA? 1000 KVA? 2000? i don't
know which one to choose correctly. Can you help?





You can't
imagine how your help can be precious to me. I was already near to give up from
this project, but after to put so many effort building machine and buying some
electronics equipment’s, is also hard to think about give up.





Waiting
your best comments, with hope to get your help,





Best
regards,





Paulo/Portugal

1
JamesF84
JamesF84

Question 5 months ago

I would also like a schematic in any form, pdf preferred- firstmailboxuno@gmail.com and if you would be so kind to estimate - what would this build cost? Mind you I have a lot of industrial components salvaged from jobs over the years including 7 variacs. So once I dig through my shelves costs may go down, but assuming all I have is the variac - what might this cost?

1
mightymousejr
mightymousejr

6 months ago

I apologize for asking a question that has been asked a million times. Can i please have the schematic emailed to me in a pdf format if you have it. If not, any format will do. Thank you for any help you can give. I cant wait to build this project.
My email is gatech1973@gmail.com

1
Helaman
Helaman

Question 7 months ago

So question... I imagine the wire gauge used on the coupling transformer(four large ferrite cores) is 6awg. According to this website, https://www.powerstream.com/Wire_Size.htm, the maximum frequency that 6awg can be operated at with 100% skin effect is 1100hz. Any frequency over 1100hz will cause there to be more effective resistance. So my question is, how do you account for the high resistance due to operating at around 50-70khz? How do you get rid of this resistance from the skin affect? As I see it, your wire around the ferrite cores will have a lot of resistance and most likely heat up and burn due to energy loss from the added resistance.

0
sattarubied33
sattarubied33

Question 7 months ago

Could you, please, send me schematics of this project? I need them for my project
thank you
sattarubied33@gmail .com

0
haritha10
haritha10

8 months ago

Hi firend!
I like your project and I believe I can do it.
Can you send me the schematic of the 30 KVA induction heater?
If possible, send me email: harith.alubaidy0@gmail.com
Thanks....

1
reihanrezaee
reihanrezaee

9 months ago

Dear Sir,

Could you, please, send me schematics of this project? I need them for my project (reihanrezaee@gmail.com)

Thank you.

Best Regards,
Reyhan rezaee.

0
aself73
aself73

Question 9 months ago on Step 3

Can this heat up and melt platinum?

0
evanjcook983
evanjcook983

Question 10 months ago on Introduction

Pardon I'm new to EE would it be possible to get a for dummies version with more detailed steps or the name of a store where i could find someone who could help.

0
goldenshuttle
goldenshuttle

Tip 1 year ago

You probably can modify single induction cooktop, replacing the pancake element with a pipe loop. This may save time and cost..what do you think ?

0
williamsurh4
williamsurh4

Question 1 year ago

Hey man, I'm doing a school project on something and I kinda need to make something like this.

Can I get any additional schematics?
My email is williamsurh4@gmail.com
Thanks

0
kendall.hallmark
kendall.hallmark

Question 1 year ago

I would appreciate a more detailed schematic, as well as specific parts that would work for the tank capacitor and the input capacitor. I also cant find (based on what I see here), where the 4 phase switch is. Please send these to kendall.hallmark@csd8.info.
Thank you.

0
andreua
andreua

1 year ago

Hi there,

Just wanted to do know is there is a way/formula to calculate the ciculating current in the coil from all the process parameters?

many thanks