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Registered Member #3283
Joined: Wed Oct 06 2010, 11:03PM
Location: Toronto, Canada
Posts: 29
Hey guys,
I'm looking to build an induction heater sometime soon but I have a few unresolved questions that I was hoping someone could answer. My main/intended use is to re-flash getters tubes.
1) Does anyone have any suggestions for a bulletproof TL494 driven design? I would like something that can continuously output 300W without stressing components. I have searched the forums and google but there doesn't seem to be a "de-facto standard" for induction heater designs. A high degree of isolation between the stages (GDTs, etc) would be nice but
2) Does the shape of the coil(Larger vs smaller dia, more turns, etc) affect output power? For my application, I'll need a relatively large diameter(3") with few number of turns (max coil height is 1.5"). Do you thing I can get 300W out of such a coil?
3) How precise is the heating within the work coil? I've noticed (in some videos) that the actual heating of the material usually takes place approx 1-2cm inside the coil. However, I have also seen incidents where a small portion outside the coil is also heated. Can this effect controllable?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
First, read this tutorial:
I started with a 1kw system and worked my way up to 12kw. 300W should be very easy.
You can use a TL494 or a 555 to drive a gate drive transformer at a 50% duty.
I think a simple helical coil is best for your application. I would use 3/8" copper tubing and make as many turns as needed to cover the work area. With your dimensions this will be close to three turns. The design I've used uses a coupling transformer to transfer mains power to the resonant tank. The more coupling transformer turns and coil turns the less current you will draw from the mains for the same output power. You will need more voltage if you wish to draw less current. Too few turns on the coupling transformer and you can develop very high currents if you unload the coil, so there is an ideal range. I would start with 20 turns on the coupling transformer and see what happens.
I have found that anything within the coil heats. I have never tried to see what happens outside of the coil.
You will have to experiment with the power level and duration to see what you actually need once you get it working.
Again, the tutorial is very detailed and will go over a lot of questions you have or will have as you proceed with the project.
You can also go to neonjohn.com He has used a Royer design with loose coupling to self-tune for tube flashing. I have not used this design, but it is another option to consider.
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Induction heater questions
