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  #21  
Old 04-29-2012, 07:07 PM
Experimentonomen Experimentonomen is offline
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The neon john circuit is a so called LCLR parallel resonant tank with a series impedance matching inductor.


When you increase the frequency, you get closer to resonance, which increases the current in the inverter, if your mosfets are undersized, they will pop as the current exceeds their ratings.

If you increase frequency even further, current should drop off again

Heres a video from my project using four IRFP450, two parallel pairs: http://www.youtube.com/watch?v=DpOcGPsennU at 1:36.

Here i have a peak detector with a current transformer showing the peak inverter current: http://www.youtube.com/watch?v=jiRwKpmBGqw

The analog meter shows the current beeing drawn from the mains.
  #22  
Old 04-29-2012, 08:43 PM
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Quote:
Originally Posted by Experimentonomen View Post
The neon john circuit is a so called LCLR parallel resonant tank with a series impedance matching inductor.


Heres a video from my project using four IRFP450, two parallel pairs: http://www.youtube.com/watch?v=DpOcGPsennU at 1:36.

Here i have a peak detector with a current transformer showing the peak inverter current: http://www.youtube.com/watch?v=jiRwKpmBGqw

The analog meter shows the current beeing drawn from the mains.
Yo! Dino De Laurentiis, is a security clearance required to post the link to Mr. Neon's schematic? His name keeps getting tossed around here but for some reason it still isn't posted ... and I have no intention of searching for it. While entertaining.. sort of... your vids don't help in resolving this thread.
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  #23  
Old 04-29-2012, 08:49 PM
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Quote:
Originally Posted by yappers View Post
To put it simply, there's no link because no such thing exist. I have an idea that I'm willing to try. That's it.
Did it ever exist?
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  #24  
Old 04-29-2012, 09:30 PM
Experimentonomen Experimentonomen is offline
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Heres a link to the circuit posted in the first post of this thread: http://www.neon-john.com/Induction/I...t_Rev_1.02.gif
  #25  
Old 04-30-2012, 01:46 AM
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Quote:
Originally Posted by Experimentonomen View Post
Heres a link to the circuit posted in the first post of this thread: http://www.neon-john.com/Induction/I...t_Rev_1.02.gif
Thanks for that. Yes, I saw it in the first post but thought it was modified from the original neon-john schematic.
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  #26  
Old 04-30-2012, 02:50 PM
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Quote:
Originally Posted by Experimentonomen View Post
The neon john circuit is a so called LCLR parallel resonant tank with a series impedance matching inductor.


When you increase the frequency, you get closer to resonance, which increases the current in the inverter, if your mosfets are undersized, they will pop as the current exceeds their ratings.

If you increase frequency even further, current should drop off again

Circulating currents within a Parallel resonant (tank) circuit are very high at resonant frequency but the external input current decreases sharply at resonance. This translates to increased Z looking into the tank. Also, the signal voltage across the tank at resonance rises sharply.


The above statements are bases on an unloaded (Hi Q) tank, while your metal stock is your load, which will lower the Q dramatically via coupling the energy into the stock.

Since you have built a working model I think you can answer the following question...

If you remove the metal stock from the crucible does the input current drop?
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  #27  
Old 05-01-2012, 07:55 AM
Experimentonomen Experimentonomen is offline
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I never tried, as that would have sent the tank circuit flying due to the voltage and current ringing up uncontrollably.
  #28  
Old 05-01-2012, 01:32 PM
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Actually, I think you pretty much answered the question. My guess is that initially input current would drop. Voltage across the tank would increase dramatically, and finally.. input current would spike when the components broke down from over voltage.
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  #29  
Old 05-01-2012, 02:00 PM
Experimentonomen Experimentonomen is offline
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Except my circuit was series resonant. I don't use the parallel resonant LCLR circuit anymore.
  #30  
Old 05-01-2012, 02:53 PM
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Quote:
Originally Posted by CDRIVE View Post
Actually, I think you pretty much answered the question. My guess is that initially input current would drop. Voltage across the tank would increase dramatically, and finally.. input current would spike when the components broke down from over voltage.
So your suspicion is that over voltage that is building up in the tank circuit is a problem? Hmm....I wonder if there's a way to calculate that voltage buildup.

Also, I tried taking a look at other induction heater design including the video that Experimentonomen just posted and there is something I that is bothering me. From what I know, the number of capacitor in the resonant tank is used to spread out the current that is going into the resonant tank, but what is bothering me is that I don't know how to determine the number of capacitors. In Neon John's schematic, it uses a set amount of capacitance, but physically, there are 24 0.022uF, 400 volt caps and 2 0.1uF 400 volt caps for a total capacity of 0.7305uF. For my purposes, I could only get my hands on some film capacitors that when put in parallel get me close to 0.66 μF. Also, here is a picture of my circuit and my coil, for those who curious

Quote:
Originally Posted by Experimentonomen View Post
Except my circuit was series resonant. I don't use the parallel resonant LCLR circuit anymore.

What was the reason? Because it sounds like you tried it
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File Type: jpg Coil.jpg (290.5 KB, 19 views)
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