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Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Hmm it doesn't like steel tubing that's too long and too wide...it draws nearly no current :( I probably need to twiddle with the work coil and coupling transformer ratios some more. And obligatory red-hot object picture:
Hi. Great project ! I built something like that but with PLL and power control. You need coupling transformer with allow you to adjust the ratio for desired power. A different ratio is needed for every specific work coil or work piece. Something like my one
I made a few connections to the primary coil to switch number of turns manually.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Awwww that's so cuuuute! *runs away and makes magic motorized tapped transformer* I'm still wondering why steel tubing (and only tubing, not solid steel) dampens the work coil so much though. Turns out drawing infinite current != effective heating...I had 20A@200V going into the inverter yesterday and the little brass rod I was trying to heat barely got warm...ohh the joys of trying to get proper coupling!
As work piece dimension getting close to coil inner diameter, the power transfer to the work piece increases. But quality factor decreases. And equivalent resistance of the coil increases. That means for relatively small work piece you need high inductor current and high ratio. But if you are heating big work piece with high ratio, the quality factor don't allow you to reach enough inductor current at present secondary voltage. So, you need increase secondary voltage by decreasing ratio.
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Big Induction Heater
