Induction heater coil impedance? - Page 1
Forum section: electronics / projects

author: CopperCone
author_rank: Super Contributor
timestamp: April 09, 2018, 05:53:24 pm
content: So the lc tuned circuit depends on c and l.I want to operate at around 50khz.Are there any good reasons towards keeping the coil with a tiny inductance and the capacitor bank with a higher capacitancee?I estimate designs i see to have coils approximately <3uh and capacitors exceeding 2uf or so.I have what i believe to be a suitable capacitor bank, but it would force me to use a coil with a higher impedance, like 15-30 uH.Other then thermal distribution along an object due to field spreading from a larger coil, are there any downsides?

author: chris_leyson
author_rank: Super Contributor
timestamp: April 09, 2018, 07:52:09 pm
content: I would expect it depends on the heating coil geometry, multi turn, single turn, pancake, hairpin or open end "C" coil. I would expect the open end "C" coil to have a much lower inductance but the open end design is a lot easier to apply to the workpiece. Just as a thought it would be nice to have an induction heater for plumbing jobs, ideally it would be an open end coil.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 09, 2018, 09:02:05 pm
content: Very low impedances, you simply can't get capacitors for. You won't do a single turn 50nH at 10kHz. Been there, talked the boss out of it, done that.For those, they use transformers mounted at the coil. Yep, microwave oven (not MOT,MO) sized transformer, lots of copper and ferrite, 100s of kVA capacity, just for a single turn coil. Hey, it gets the process running, that matters first...Needless to say, it's not very portable. There are some handheld transformers out there, usually with counterweighting (skyhook) to make them practical.50kHz, 0.2uH and 20uF are reasonable values.The impedance is low (sqrt((0.2uH) / (20uF)) = 0.1 ohm, so a resistance of 10mohm comes at Q = 10). Preferably, use a series resonant topology, toroidal transformer (single turn secondary) to match to the inverter. Several taps on the primary to choose matching as needed.Quote from: chris_leyson on April 09, 2018, 07:52:09 pmI have a proposal for a handheld version, that could replace propane torches (fire hazard?) in tight spots, maybe cheaper operating cost too?Tim

author: chris_leyson
author_rank: Super Contributor
timestamp: April 09, 2018, 10:32:52 pm
content: QuoteNice one Tim, I hope it works outFor practical reasons I would prefer an open coil for the "work" coil, but would have to fabricate a few coils to get an idea as to what inductance to expect. A toroid around a copper bar is by far the easiest impedance matching solution but it's going to be huge to keep the flux density down, several toroids in series would fix that. Just for fun I will have to have a stab at "running the numbers" at 50kHz or 100kHz.What sort of coil current do I need ? Probably a few 100A or more if you're coupling magnetically into copper... it's all down to the "work" coil and it's magnetic coupling efficiency. I think direct resistive heating looks like a much better solution for heating copper pipe.

author: tecman
author_rank: Frequent Contributor
timestamp: April 10, 2018, 12:08:30 pm
content: QuoteYou mean something like this:https://www.amazon.com/Induction-Innovations-MD-700-Mini-Ductor-Magnetic/dp/B008XN9HO6/ref=sr_1_2?ie=UTF8&qid=1523361791&sr=8-2&keywords=bolt+induction+heater&dpID=41zIXPAwPfL&preST=_SY300_QL70_&dpSrc=srchpaul

author: CopperCone
author_rank: Super Contributor
timestamp: April 10, 2018, 01:45:49 pm
content: A milwakee one powered by m18 batteries would be nice. Possibly two batteries.I cant wait to get their portable soldering iron and portable heat gun...I love that tool brand.If someone could estimate the power draw/specs that are possible with one of those m18 batteries it would be possible to reverse engineer or steal an existing milwakee tools battery drain protection system and use it with a small portable zvs heater fairly easily. The self commutating typeIfogure that battery can give you 500w of power for a while.. Maybe more.The new dewalt higher voltage batteries would be good too. Their new angle grinder is an absolute beast, i love using it.