Induction Heater

[the iron dwarf]

looking quite good now

 

[James Bond]

Everything seems to work fine, I try to work with a complete bridge inverter
But I have several problems,
The most important of them is the following, when the piece begins to heat its resistance begins to decrease and as it is in resonance the current rises to high levels so that I need a good control of current,
Going out of resonance frequency does not seem a good method to me since this stresses a lot to the igbts and the power factor is bad.
I would not like to use a controlled rectifier as it would increase my costs by having to buy half power scr as well as generate pulses and blabla bla
The real problem lies in the topology .... since it is the most common topology and most used by home induction furnaces.
Is a good topology but it has weak points

a disadvantage of this kind of topology is that the heater will pull huge current when it run at nun load situation.and you have to put a current limiter to protecting your circuit in fact your heater power has hardly increasing with decreasing of load resistance.

LCLR matching network has a gear ratio that varies with load resistance.actualy when you put a heavy load into the workcoil the gear ratio will be highest and your current will be low.and reverse in null load. and also your resonant frequency will be change .

another disadvantage of this stuff is that for increasing the output power you have to decrease your matching inductor value and this is not good beacause the matching inductor supresses the current spiks of the inverter .and when you decrease. it cause this current spiks to damage your transistors

 

[James Bond]

i have a idea but i need time

u will see

[bajajoaquin]

I really wish I had the electronics skills to attempt this. I think it might be kind of like how hot rodders really feared fuel injection when it came onto the scene. Induction heating isn't new technology, and the things to make it happen are available in the marketplace. There's no reason other than experience and technical skill that more people shouldn't be making induction heaters. Both of those are reasonable to acquire for normal people.

Keep us posted!

[James Bond]

i finish the full bridge inverter  

i have some problems but i think we are ready 

i think this induction heater cosumes 20amp at 120v 1phase i will  show you a video.

[bajajoaquin]

Any updates?

[James Bond]

oh yes, friday i will post.

[James Bond]

since now I'm using a pair module igbt. and im workin with 240vca.  and i have a new board too.

 

 

Im working at 245vca  and the induction heater consume 25 to 23 amps.  6KW  of power   for small pieces its ok !!     i can melt 5 or 6 oz of cuper in 5 miutes 

i think its a big step.  

this induction heater works fine very well but if i want go to higer levels 15 kw for example i need to do another topology  but not  now maybe 2018.

[ReactorForge]

On 11/27/2017 at 7:00 PM, James Bond said:

since now I'm using a pair module igbt. and im workin with 240vca.  and i have a new board too.

Im working at 245vca  and the induction heater consume 25 to 23 amps.  6KW  of power   for small pieces its ok !!     i can melt 5 or 6 oz of cuper in 5 miutes 

i think its a big step.  

this induction heater works fine very well but if i want go to higer levels 15 kw for example i need to do another topology  but not  now maybe 2018.

Great job James!

It looks like you have tackled most of the challenges you faced in the beginning, a significant step indeed! I see a few things I want to point out that helped me and hopefully, they will help you too. I am close to publishing all the info about the ReactorForge on GitHub and the website. But you have come a long way, and yours is the closest I've seen to what I built, so I wanted to share this much at least.

I'll start with the mains input and work my way to the work coil.

1. I'm sure it's just a test setup, maybe you had a variac hooked up in this photo, but definitely up your wire gauge into the rectifier. Pulling 25 amps at 240 volts is more than enough power to heat up wire that size and melt the solder joints on those alligator clips. Again I'm sure you knew this already.
2. Join the rectifier to the IGBT bus using the same copper strips you used to join the two IGBT's together to lower inductance even further on your DC bus.
3. Speaking of DC, kudos on not using a filter cap on the DC busbar. The IGBT's and tank don't mind that 120Hz pulsing DC, and it helps maintain a power factor closer to unity!
4. It looks like your still driving your IGBT's with gate transformers. They are great for a lot of things and easy to work with, but I highly recommend switching to a hybrid driver. They are much safer and will extend the life of your IGBT's. Preventing a crowbar, "shoot through" situation among other features is critical when you are pushing the limits of power in a noisy environment.
5. If you are still using a PLL to lock onto your resonant frequency, you are limiting your dynamic range of the coil size, workpiece load, etc. In short, the inductance of the work coil is restricted since your passive components lock you into a tuneable range like in imsmooth's circuit here http://inductionheatertutorial.com. It is also affected by extreme swings in ambient temperature depending on your passive elements and layout. I've got an excellent method using an Atmel power stage controller as a pseudo software PLL. It has the added benefit of allowing you to monitor for many other types of situations in software as well. I'll be sharing all my code for that on GitHub soon too! (I will likely make individual repositories for the new cleaned up versions.)
6. You are using the tank capacitor voltage for your resonant control logic. While there is nothing explicitly wrong with this method, you would benefit by switching from monitoring tank voltage to tank current. Do this by adding a current transformer to one of the inverter legs feeding the matching transformer. As you know, the tank voltage in a series resonant setup gets VERY high! From a signal conditioning perspective, this is an irritating and inefficient problem. Using this method you also get the added benefit of being able to monitor inverter current if you split and condition your signal correctly. Check out the schematic of the ReactorForge CriticalMass for an example of one way to accomplish this.
7. Your matching transformer appears to be a bit small and is probably saturating at high power levels (or likely will if you try to go beyond 6KVA). (Usually indicated by distorted secondary output.) You can stack multiple E cores to increase flux density and make sure to use a ferrite material rated for high frequency (at least 100Khz) such as 3C85, 90, etc. and have a high AL value. Operating in a constant or occasional saturated state isn't necessarily a deal killer as many Chinese units tend to run like this. This use of this method is one reason why they have copper plates and cooling lines on the transformers. I think this is a cheap cop-out way of driving the tank though.
8. The tank bus lines need to be closer together. You are introducing a lot of inductance and wasting power as well as heating up any surrounding metals including the lines themselves, transformer, capacitor, etc. The series topology can be a difficult one to get the lines close, but it's doable. Something like this is what I used: https://imgur.com/a/oWSK6

I also noticed your LCD display says "POWER 0%". I know you aren't monitoring the mains or inverter current (at least not in this photo) but are you control the average inverter power output level? If yes what methods have you tried (PDM, Phase Shifting, Frequency Shifting, etc.)? The issue of power control get's interesting at very high power levels, generally above 8-10KW or so.

Keep up the great work James! I can't wait to see how far you take this next year. 

- Joshua Campbell

[James Bond]

On 11/28/2017 at 1:17 PM, ReactorForge said:

Please STOP all the excessive unnecessary quoting of the post directly before yours it wastes bandwidth

 

Please repost in a normal text format

 

[James Bond]

29 minutes ago, James Bond said:

 

ok let's se
point 1:  come on!! a Variac !?!  come on........... 220VAC line
point 2: That is a good idea
point 3:  I don't have a power factor meter but each blue cap are 1uf/250vca so i have 2uf total.
point 4:   yea! GDT!!!!. hybrid drive are very expensive  and you need 4 and 4 
dc-dc powers supply if you know for some cheap let me know.
point  5:  we  need to discusse this point.
I'm working with  pic microchip and i have a range from 10khz to 500khz . i dont know anything of Atmel microchip but i understand a little bit your power stage controll and im in love with this ...it's a shame that in the web nobody explain the power stage controll.   in mexico nobody knows about atmel.  
you can controll the power of your unit always at resonance... boss!
point 6:  well i can do this ..but later 
point  7:ok i have two more that I can stack. i think i'm saturating this one . they are 3c90 material
chinese units haha
point  8:    thanks i have to do that

my new friend josh thanks for your time and help me

 

[James Bond]

[James Bond]

when i heat some material the current rises and it can be dangerous i need a current control.

first i need mesure current.   

if a have advances i will post .

 

[ReactorForge]

Bandwidth - I never really thought of it as a waste of bandwidth, I did leave out the photo. Even though the quoted text was directly before my post, I like to make sure the context of my writing is known. But I won't do that on your topic anymore. Also, the window has closed for me to edit it so only a mod can remove it now. I don't want to delete the post and resubmit it because then things would just be out of order. Maybe we take bandwidth for granted in this country sometimes!

Mod addition:   Since you are not aware, let me inform you that many of the over 150 countries we service are places that still have dial up, and pay by bandwidth used.  In the USA many take it for granted having high speed and unlimited bandwidth,  Others do not have this luxury,  try to be considerate of others, 

---

Point 1: Yes a variac! Very helpful in testing WHEN things go wrong. Your parts are less explodey if the variac is turned down lol. (I only asked because of the alligator clips on the rectifier, the only time I see that on mine is when the variac is hooked up.)

Point 3: You're good. The small snubber capacitors on the IGBT's are necessary to suppress high transient voltage spikes on the bus during switching. They are too small to have any noticeable influence on power factor. 

   Note: You probably already know this, but you can use an oscilloscope to view the power factor since it is just the true power over apparent power or the cosine of the phase angle delta between voltage and current waveforms (see photo). You just need a current transformer on the mains with a burden resistor and two scope probes, one on voltage and one on the CT.

 

Point 4: Yes these are very expensive to buy completed, but it looks like you have the means make PCBs. I included the board files, BOM and description in the wiki for the open source hybrid driver I'm using here: https://github.com/ThingEngineer/ReactorForge/tree/master/hardware/Hybrid Driver You can buy the ISOLATED_DC_DC_CONVERTER and HYBRID-IC-IBGT-GATE-DRIVER at a decent price from China (https://www.alibaba.com) for example and the passives from where ever. If you want to go to higher power levels, you don't have a choice. The TON and TOFF time delay with a GTD will not work under extreme load. Your IGBTs will likely shoot through and explode. I'm not saying it's impossible with GDTs, but it's much easier, cleaner, and safer with hybrid drivers.

Point 5: I'm working on a neatly documented write up (Instructables style) on precisely this to post on the ReactorForge website. It's the key to being able to make an IH that will be useful in a real shop no just on the bench for hot metal porn. The PLL is too restrictive, one could say that implementing digitally controlled passives could expand the PLLs dynamic range but that is just complicating an already complicate and sensitive circuit in my opinion. PIC makes excellent chips too, but they don't yet have a comparable power stage controller unless you count the fact that Microchip now owns Atmel. Read more about them here:

• AT90PWM216-316_Datasheet
• ATMEL PSC Cookbook Application Note

Point 6: Similar to the gate driver issue, this is needed even more so at higher power levels.

You're very welcome and keep up the good work.

[James Bond]

Reactor forge its amazing.! good job

[James Bond]

On 12/1/2017 at 3:20 PM, ReactorForge said:

Mod addition:   Since you are not aware, let me inform you that many of the over 150 countries we service are places that still have dial up, and pay by bandwidth used.  In the USA many take it for granted having high speed and unlimited bandwidth,  Others do not have this luxury,  try to be considerate of others, 

you just Had to quote the entire thing again didnt you ?

I am not the great student of electronics that you think and I do not know many things about many subjects.
My main problem is that I do not know many people who know about the subject of induction furnaces.
I would like to have some mail or something to be in contact with you.
Today I have several doubts.
I have seen a material called flux that serves to concentrate the field of induction coils. it is very expensive. Is it possible that some more common material will be useful for this experiment to concentrate?
since for example I would like to make a coil like the induction heaters but concentrating the field above the coil.
I am trying to make a current sensor by measuring the input current from the input line and not from the inverter. is this ok?

[ReactorForge]

Don't underestimate yourself. Some of times greatest minds were self-educated! You're doing a great job, just be safe, keep failing, and keep learning! You won't run into too many people on the streets who specifically "know about" induction heaters but that doesn't mean you can't confer with other like-minded people about electronics in general. The induction heater circuit overall is a very fundamental and beautiful thing really. It's like nature wanted it to exist! 

My email is on my Github page. Shoot me a message, I have a book I want to send you that will help. 

Yes, there is a material you can use to concentrate the magnetic lines of flux called ferrite. It's the same or similar material used in your matching transformer. It doesn't heat up as nearly much as say a ferrous piece of metal would because it's ferrous particles are isolated from each other with a ceramic thus preventing eddy currents and I^2R heating. John DeArmond with fluxeon.com (NeonJohn) uses this in one of his models calling it a flux concentrator. It works basically like this; the crude drawings show the magnetic lines of flux in an induction heater coil with an open coil and one with a "flux concentrator". If you use this method you must take into account the fact that the ferrite "loads" the work coil much more than any workpiece. You must account for this by changing the impedance of your matching transformer (fewer turns on the secondary, more on the primary, etc etc).  It also lowers the resonant frequency of the tank so you might even need a lower value capacitor to raise it back up, unless you want it lower... It's an interesting thing to experiment with, I recommend it. I don't really recommend it's use in a metalsmithing role but it does have its advantage. For example, it's amazing for brazing small parts, like copper tubes to make other induction heater coils.

Yes, current sensing to determine the power consumption of the induction heater overall should be done on the mains side, the input line. Current sensing on the inverter side would give you the oscillating current of the tank. That's the big number you see on the front of most induction heaters that usually ranges from 200-800 called the "working current". A current transformer on the inverter side also gives you the ability to do current zero-cross detection of the tank. Compare this to the voltage zero-cross (your inverter switching time) and with some clever use of timers you can deduce the resonant point without a PLL!

[Glenn]

James Bond

The quote feature explains how the quote works.

Think of it as reading a book. You read a paragraph and move on to the next paragraph. With quoting what you just read, you are then forced to re-read that paragraph again before you can move on. You did not forget what you just read, so why be forced to read it twice?

For those on slow modems, or a  pay to play connection, this means you are paying full price but charged for a double download, and in effect getting only half the information you paid for. 

Use the quote feature when needed, and please be courteous to others in the process.

[James Bond]

hi my friend joshua on the internet I have seen some very interesting concentrators.  for example the induction cookers
They have some ferrites under their coil that I suppose serve to concentrate the magnetic field upwards of the coil and in this way do not waste energy.
I am right?
I send you an email my email is email removed
I attach an image and a link to a video on youtube 3:16

https://www.youtube.com/watch?time_continue=5&v=jOg8Q-jt1BY

https://www.youtube.com/watch?time_continue=2&v=Dsc8vzSQDP8

 

[ReactorForge]

You are very welcome my friend. 

Those videos were interesting. Here at 5:58 you can see the animation of how the ferrite material carries the lines of flux.  

That second video cool as well. It's intriguing how the ferrite material was incorporated into a sort of clay or foam that you can mold onto the coil, allowing you focus the flux on one side. It looked like it started to get hot and smoke in the end though, or maybe that was just smoke rising from the metal.

Whether it's a permanent magnet or an induction heater coil. Any time you introduce a ferromagnetic metal (iron, nickel, or cobalt) to its lines of magnetic flux (called a vector field), those field lines want to flow through the material with a higher relative permeability. Since those ferromagnetic metals have a much higher permeability than the surrounding air, they choose this as the "easiest" path to traverse. Similar to the way electrons prefer to flow through the path of least resistance.

 

CORRECTION: In a previous post I mentioned that a variac provides isolation from mains. I want to point out that only an isolation type autotransformer or a separate isolation transformer in front of the variac will provide this isolation and most variacs are only autotransformers. You can ask the google machine for more info if you want it.

[ReactorForge]

James,

You were interested in using ferrite material to focus the induction heaters flux. This site shows the application of EMS for SolidWorks to model the magnetic flux density in the radial ferrite cores under an inductive cooking coil. There are other programs you can use to model various magnetic characteristics such as MATLAB

https://www.emworks.com/blog/induction-heating/induction-heating-engineers-empower-chefs#comment-9491

Two amusing things about this site's post though, for one they plagiarized a screenshot from one of my youtube videos (the very first photo in the post), and two they called the ferrite cores iron cores.

 This note was requested by ReactorForge: I see now that rather than saying "Two amusing things about this site's post though" I should have worded it like, "There are two amusing things about the post from the site linked above."

If they were made of iron, they would burn the coils up as iron would succumb to i2r heating from the induced eddy currents.

Here is another company that specializes in controlling magnetic flux distribution in induction heater work coils. 

https://fluxtrol.com/magnetic-flux-control-in-induction-heating

[James Bond]

ok i was very bussy this weeks because my job its very demanding,

but i finally finish the new control, it works very fine in the induction heater because my goal is to maintain the current stable no matters the size of the piece or the heat or the material and i can say this thing works fine.

also i introduce a safty control if something gone wrong.

 

[James Bond]

well i was  workig in the control of the induction heater and i put a lcd 16x2 so you can set power and time before start work,

i change the tank circuit  because my friend Joshua C. told me than the old one waste a lot of energy. and  he was right.

cooler sistem its a very bad idea but works fine four 12vdc high flow fans and  two computer radiators. jeje thanks Joshua C.

the system works grate at 4 kw and and I think we can get up to 7kw. 

 

 

 

 

[James Bond]