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4KW Induction Heater

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Linas

Tue Jan 24 2012, 05:49PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

if i want melt cobalt/iron material, and reach 2500^C, what kind of frequency and power should i use ?
i already have some heavy capacitor Celem 1uF 650A 550V capacitor and 60A ultra-fast IGBT for this project with some nice TC4422-TC4421 drivers.

and what kind of driver to use ? i have idea to use zvs controller, so i can regulate power by changing frequency above resonance, and if i need more power, just get close to Fo.
zvs driver would be MC33067P

Dr. ISOTOP

Tue Jan 24 2012, 08:39PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Linas wrote ...

if i want melt cobalt/iron material, and reach 2500^C, what kind of frequency and power should i use ?
i already have some heavy capacitor Celem 1uF 650A 550V capacitor and 60A ultra-fast IGBT for this project with some nice TC4422-TC4421 drivers.

Melting steel will require somewhere around 10KW and a nice crucible (I couldn't do it at 4KW {the limit of a 120V outlet}).
I would strongly recommend a half/full bridge with either a fixed-frequency TL494 driver or a PLL driver (or primary current feedback the way the DRSSTCs do it).

Tonskulus

Wed Feb 01 2012, 06:03PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

power requirement for melting steel, it all depends on amount of steel to be melted.
2kW is enough for quite small amounts when using good and sealed curcibles..

I used 1dl curcible and have been melting several different metals with it, using 2-3kW of input power.

Gabriel35

Fri Feb 17 2012, 01:14AM

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

Pretty Huge version!
I like It!

I got some new UPS transformers over here, and i think i'll start all the IH fun Again!

Just waiting for the right caps !

tanc

Thu Nov 09 2017, 10:55AM

Registered Member #54853 Joined: Tue Apr 14 2015, 08:08PM
Location:
Posts: 7

Hi everypeeps, firstly thanks for the wealth of info here, it has been a massive help as I too have built a parallel irfp260 'marco' IH. secondly truly amazing work from so many people.

reading through this thread i am particularly interested in the lm311/ne555/shunt protection circuit that marco talks of and how it can save 'countless mosfet' ( i am one the mosfet graveyard community). Can someone point me at a diagram that integrated this to marcos circuit?

my system is 10A variac, 140A ac arc welder, 100A rectifier, 4*irfp 260, 6.28uf and 5 turn 3.4uh which calculates to about 30khz.

in an effort to avoid any more misfit deaths I am reluctant to turn everything up to 11 but at the same time my challenge is to melt glass in a graphite crucible.

last night it ran for 3 hours drawing 800w from the mains at 30vdc and 20-25 amps. this was enough to melt copper but not glass. in marcos film it looks like a steel bolt is bubbling which usually happens just prior to melting which would indicate 1200c?

so my question is what voltage and current should i be aiming for to achieve this temperature and what are the sensible maximums for these parameters to avoid fireworks?

any help in this direction would be very, very much appreciated

RogerInOhio

Thu Nov 09 2017, 03:14PM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

It's hard to believe it's been almost 6 years since I started this thread. I have blown up plenty of MOSFETs with this heater but I have learned a few things that seem to have helped recently. The most common problem I would have is that at start up both MOSFETS would turn on at the same time. Making one of the gate bias resisters a little different value than the other (by about 10 percent) seems to help. Also I have been told that it's best to have the circuit turn on rapidly rather than have the voltage come up gradually on it.

Tanc, I have never tried to melt anything so I cant be much help there.

tanc

Fri Nov 17 2017, 08:59PM

Registered Member #54853 Joined: Tue Apr 14 2015, 08:08PM
Location:
Posts: 7

Hi Roger,

Thank so much for the reply, it seems i am a few years behind most people on this!

I have i think by hapless luck and wholly persistence had a few days of success. I could not find any over current protection circuits that looked simple enough for me but whilst looking it occurred to me that if i can't have over current protection I can have under voltage protection. I had purchased some LM311 in anticipation of following Marcos advise and tried to arrange a voltage comparator that opens a relay that powers the varian. It runs off its own 24v psu and sure enough when the load gets too much the voltage drops and the varian turns off. Very simple. Not ideal I know but it has saved 10 mosfets since installation so it can stay for the time being.

I have doubled up on the IRFP260s and added large, thin copper sheet directly under them in the path of the forced air.

Today it has been running at 50v and 45a (>2kw) and have quite quickly melted iron. Sadly not hot enough to pour but definitely 1 homogenous lump in the bottom as opposed to the jar full of CI swarf the went in.

At the moment I have a 10A variac feeding a 140A ac arc welder which is about a 1:6 step down and with the load in I have to have the variac turned up full and the heater pulls the voltage down to about 45v-50v and draws 45A ac from the welder.

How can I double the power? (I need to generate 1600 deg celsius for the current task)

Also can you explain the coupling transformer that some design use in terms of what its for, where to put it in the circuit how to decide what it is made from and how many cores,turns,henries etc it needs to be?

here is a happy picture of todays success

RogerInOhio

Sat Nov 18 2017, 04:40PM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

Hi Tanc, Im glad to see things are going well . Id'd say you are doing real good to be getting 2 KW out of your system. It seems to me that if you want significantly more power it would be best to go with a circuit that uses IGBTs. The IRFP260 is a low voltage beast so the impedance of your work coil is going to limit your output no mater how many you use.

I have been wanting to build a more powerful induction heater myself and what I might do is start with a DRSST and convert it into an induction heater. I know that sounds stupid but I'm not good at designing circuits and you can buy everything you need for a DRSST premade . Don't laugh, I'm the guy that just made a crappy Tesla coil by hooking up a primary coil with a secondary coil to a induction cooker circuit board that I bought off of eBay. You cant get an more lazy than that.

Sulaiman

Sat Nov 18 2017, 04:56PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Whatever you heat in an induction heater, for a fixed heating power,
the maximum temperature is determined only by heat loss,
conduction and convection losses will dominate at lower temperatures with radiated heat loss setting the upper limit.

I would expect the rate of heat/energy absorbtion will drop off dramatically as iron passes its Curie Point (c770 C) and changes from ferromagnetic to paramagnetic.

Based on general principles, not induction heating experience - verify.

tanc

Wed Nov 22 2017, 10:08AM

Registered Member #54853 Joined: Tue Apr 14 2015, 08:08PM
Location:
Posts: 7

Hi Roger, Thanks again for the quick reply. Its a shame to read what you wrote about the IRFP 260 as i have just replenished my stock and now feel that I know the circuit quite well. Also I have been reading this post from top to bottom several times and had decided to follow your project to try for 4 kw. Your video seems to heat that pipe extremely quickly and I can't help but think if there was an insulated crucible in the coil that ir would be able to pour iron with ease. do you still have the schematics and if so would send me a copy?

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