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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Artlav wrote ...
For that case you warned to "make sure you do not saturate the core" - what would be the symptoms of that?
You will lose output power despite increased current draw on the input side.
The nice clean sinusoidal waveform will get very distorted.
If you want a nice simple circuit why don't you build the 3kw unit I show. It's cheap and easy to build. You can easily melt nuts and bolts. The only drawback is you have to manually tune it to resonance and track it as you move towards the curie point.
Registered Member #8120
Joined: Thu Nov 15 2012, 06:06PM
Location: Moscow, Russia
Posts: 94
Ash Small wrote ... Do you have a signal generator? can you do a sweep to find the resonant frequency of your tank circuit?
Sure. That's how i found it in the first place. It will wander with load and it's condition, however, so on-the-run tuning is necessary.
IamSmooth wrote ... You will lose output power despite increased current draw on the input side.
Hm. Why? As you describe here , it is a valid method of power control and tuning for specific kind of metal to use.
EDIT: Oh, read that wrong. I thought it was about changing turns on the coupling transformer.
Anyway, that's not a very important question, since i only need it for testing at low voltage.
IamSmooth wrote ... If you want a nice simple circuit why don't you build the 3kw unit I show. It's cheap and easy to build. You can easily melt nuts and bolts.
Yeah, i'm getting there. The Instructables design looks more and more like an overcomplex water heater than something useful. Even the gate drive circuit is nearly worthless, and there is no protection against anything failing.
IamSmooth wrote ... The only drawback is you have to manually tune it to resonance and track it as you move towards the curie point.
Really? I thought you had a PLL to take care of that?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Artlav wrote ...
I thought you had a PLL to take care of that?
The 12kw unit had the PLL/uP and will lock and track resonance all on its own. The 3kw unit just has a PLL. While this will get you close to the resonant frequency on its own, it is not exact and needs tuning as the metal heats if you want the most efficiency and least risk of blowing your switches
This is a simple, solid unit that will give you hours and hours of fun melting all kinds of junk. The unit works. Other than the capacitors, all the parts are inexpensive.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Do I understand correctly that power is controlled by the pot that controls the PWM and that tuning is controlled by the pot that controls frequency?
If it's really that simple you can control it using a 'scope and a X10 probe, just adjust the frequency for maximum amplitude, then turn up the power as high as necessary/you dare!
If I'm correct I might build a smaller one along these lines
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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I'm not looking at the schematic but one pot controls the upper and lower bounds of the frequency range which is determined by the workpiece and coil
The second pot controls the actual frequency which does determine the power Maximum power transfer occurs at resonance
Yes you to use a scope to monitor the frequency and resonant waveform You simultaneously look at the coupling current and inverter voltage And look for the proper phasing Which should be slightly above residence
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
IamSmooth wrote ...
I'm not looking at the schematic but one pot controls the upper and lower bounds of the frequency range which is determined by the workpiece and coil
The second pot controls the actual frequency which does determine the power Maximum power transfer occurs at resonance
Yes you to use a scope to monitor the frequency and resonant waveform You simultaneously look at the coupling current and inverter voltage And look for the proper phasing Which should be slightly above residence
Ok, I assumed the one that controls dead time controlled PWM, and the other controlled frequency.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Ash Small wrote ...
Ok, I assumed the one that controls dead time controlled PWM, and the other controlled frequency.
I'll have to look into it a bit further.
If you look at the PLL datasheet, the resistor values control the range of frequencies the PLL will explore for a lock. The tighter the range, the better the control. The larger the range the more flexibility one has for sticking a random workpiece in the coil and getting a lock.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
IamSmooth wrote ...
Ash Small wrote ...
Ok, I assumed the one that controls dead time controlled PWM, and the other controlled frequency.
I'll have to look into it a bit further.
If you look at the PLL datasheet, the resistor values control the range of frequencies the PLL will explore for a lock. The tighter the range, the better the control. The larger the range the more flexibility one has for sticking a random workpiece in the coil and getting a lock.
I think we may have our wires crossed somewhere, I Am, I was under the impression that the circuit we were discussing has no PLL
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Induction heater from Instructables, or what determines the current draw?
