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Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
Time to build up new induction heater. My goal is to make compact table top unit for small brazing, soldering etc purposes. So far i have succesfully made first prototype. Im very pleased about the results. Final version will be equipped with two parallel connected 811A's. The circuit itself is parallel connected Colpitts oscillator. Tankcoil is surrounded by singleturn coppersheet (currently its aluminium but will be made out of copper) secondary coil. This method will provide hundreds of RF amperes to workcoil. Powersupply is MOT giving 2kV for plate, halfwave rectifier is used there. Ok, some pictures and video:
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Wow. I find that really cool because the design is so simple. How much power are you drawing and at what freq? Does the one turn sec get hot at all? How about the tank caps? I may have to try this some day.
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
Myke wrote ...
Wow. I find that really cool because the design is so simple. How much power are you drawing and at what freq? Does the one turn sec get hot at all? How about the tank caps? I may have to try this some day.
Currently, resonant frequency is around 340kHz. Im going to retune it up to 1MHz. Thus, i can use smaller 1-2t workcoils.. I havent measured input power, maybe 300watts using just one tube. Secondary will get warm, it will be made out of copper in final version. It may require watercooling as soon as two tubes are used.
Component values are not optimized yet but seems to be ok for one tube.
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
I made some improvements for my prototype. Just some fine tuning. Now it can almost melt some small workpieces, screws etc, using single 811A! I think its now tuned to its maximum. Tube is also staying cool, no overheating (redding plate) problems at all.
Soon I will put the whole thing to a small metallic enclosure. It will be nice and compact induction heater to be used for many purposes like soldering, brazing, heat treating and so on.
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
Plasmana wrote ...
That is so cool!
I didn't think tubes can be used in induction heating. I must give this a go as I got a couple of 811A's awaiting to be used in my VTTC.
Vacuum tubes are used to power induction heaters for more than 70years.. And some manufacturers are still using this method for induction heating RF generators.
Check out ebay.com and search "induction heater", most of them are using vacuun tube oscillators :)
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
Dr. Kilovolt wrote ...
What about this, could be a simpler design with less caps and no series choke.
Maybe it works as well.. I just dont like that idea where primary/tank coil is HOT (live). If, for some reason, primary arcs to secondary, there will be full plate voltage @ workcoil!
Thats why im using capacitor between tube and tank circuit (and it also requires that RFC beetween psu and plate). For me, its not a problem. Just takes some more space...
However almost any oscillator type should work, its just the safety!
Grid coupled, hartley and colpitts oscillators are the most common induction heater oscillators.
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Small induction heater using 811A
