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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The cheapest way to get an accurate answer is with a plug-in energy meter like the "Kill-A-Watt". This is an American trade name but similar devices are available worldwide for about $30. The ones I know of all do a proper calculation of real power, taking displacement and harmonic power factors into account.
Registered Member #8120
Joined: Thu Nov 15 2012, 06:06PM
Location: Moscow, Russia
Posts: 94
And it is preliminarily complete and able to run at full power. Haven't tried melting anything yet. Max attempted run time so far is only 20 seconds at full power, with no signs of heating anywhere but tank capacitors. Water can test shows 1100W heat output at 284V, 8A (DC) input. The tuning is somewhat tricky, and i wouldn't trust it near a curie point, but i think i can try getting something red-hot as soon as i get a heat-resistive stand to do it on.
At least try it as far as tank capacitors would survive.
The tank capacitors are getting hot rapidly, from ambient to +40*C in 20 seconds, despite being attached to big piece of 10*C water-cooled copper. Their leads glow brightly on the thermal camera when on.
I guess i'll have to replace them, but the question is - with what? These are the best i can get, so only way out is to get more of the smaller ones.
Overview:
Bridge, top. The IGBT bricks are metal-cold with water cooling, looks like they are quite an overkill for a project this size. But i had no other use for them.
Bridge, side. The neon bulb is the danger light for the input capacitors.
Tank capacitors. 11x0.1uF, 2000V polypropylene.
Tank coil. 8 turns, 120mm diameter, 6 mm pipe.
Driver circuit. Instructables-derived TL494 oscillator, Steve ward's N-FET/P-FET IGBT driver.
Input and inrush current limiting - precharge through a big resistor for 2 seconds, then flip the power switch. If you flip the switch at once then as the 3300uF input capacitor fills, the local breaker will pop, the outlet breaker will pop, and the building breaker is likely to pop.
The cooling system. The water just circulates in and out of the bucket, enough thermal mass in there for the short tests i do so far.
Bonus: A can in the coil, getting warm and ir-glowy. Looked much nicer on the camera screen...
Verdict: The Instructables design can become a dead simple high power induction heater, if you tweak it just right. But it's a lot of tinkering with not too much hot fun.
Registered Member #8120
Joined: Thu Nov 15 2012, 06:06PM
Location: Moscow, Russia
Posts: 94
Speak of the devil. Just after posting the above i tried to melt a slab of solder. 10 seconds at full power, and the tank capacitors started making cracking sounds, then the breakers blew.
No visible damage, but the frequency is way off. Apparently some of them failed internally.
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Induction heater from Instructables, or what determines the current draw?
The tank capacitor is the hardest part of the induction heater to get right.
