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Quince
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You can buy a decent scope for $100 on eBay.
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Contrabasso
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Can I actually and legally buy a small (1kW max) induction furnace? ebay? mail order? UK supplier?
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microcosmicus
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Legality isn't an issue unless you were planning to steal a furnace.
Rather the problem is in finding a furnace of that size ---- AFAIK,
the overwhelming majority of induction furnaces are much bigger
affairs used in places such as foundries or scrap metal recyclers.
You might have better luck finding yourself an induction heater
such as is used for heat treatment of small parts and similar small
jobs, then building a small furnace from copper pipe and refractory
material which could be connected to the power supply of the heater.
For instance, here is an advertisement for an induction heater in
the power range you are interested in:
http://djvmerchandise.com/pro1161217.html
If you look around, you might find one for a lower price or locate
a used unit for sale.
[Edited on 6-4-2008 by microcosmicus]
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Twospoons
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Better still, get a portable bench-top induction cooker (~$100 used), gut it, and rebuild into a furnace. That should be good for 1-2 kW.
Helicopter: "helico" -> spiral, "pter" -> with wings
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evil_lurker
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| Quote: | Originally posted by Twospoons
Better still, get a portable bench-top induction cooker (~$100 used), gut it, and rebuild into a furnace. That should be good for 1-2 kW.
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That is what I was thinking.
You could theoretically cast a small refractory furnace, put a steel or iron plate in the bottom, and then use it to melt aluminum or other low m.p.
metals.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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12AX7
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Sadly, induction cooktops aren't the right impedance or frequency to operate the kind of coils needed for a furnace or other general work.
Tim
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microcosmicus
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More specifically, since they work via the magnetization of iron,
they won't do diddlysquat above the Curie point of iron. Hence, if
you did as you proposed with the iron plate, you would find out
that your furnace would not go above 770C.
While such a furnace would not be good enough for tasks like
welting steel or brass, it should work for melting low melting
point metals, calcining, dehydrating, pyrolysis. annealing glass,
firing earthenware and other such applications around the lab.
For higher temperatures, you need to make use of the skin effect,
which means radio frequency.
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12AX7
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Induction Heating
Induction heating has come up here on occasion. I thought some might be interested in the recent progress I've had.
This is the 1kW unit:
It works, oh yes it does: this is a tablet of graphite heated to about 1100°C. (It's actually glowing yellow, the camera saturates to white. The
glow seen around edges is more representative.)
But what good are pictures? How about some action! Not to disappoint, I have some video:
http://www.youtube.com/watch?v=ro6Dt9g7Ohw
My project also appears on hack_a_day:
http://hackaday.com/2009/06/22/induction-furnace/
Now, the interesting part is this: I'm getting ready to offer kits and finished units for sale. First, the 1kW model seen above. Models up to 10kW
later. Keep in mind this is an advanced project and requires more than a VOM to put together. If anyone is interested, drop me a line.
Tim
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watson.fawkes
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Are you still using the same circuits whose schematics you posted here?: http://webpages.charter.net/dawill/tmoranwms/Elec_IndHeat6.h...
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Dr.3vil
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Fantastic Job, I was just about to link your story from hackaday too. Im really impressed and would love to build one (cash permitting). I would
consider adding digital controls and preset ability with a PIC or Ardunio..USB?..
DR.3vil
- Paper chemistry works the first time every time -
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12AX7
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I'd go with something Atmel (rather than use an Arduino, I'd cook my own hardware), PICs are stupid.
Schematics are new; unfortunately I may refrain from posting them. At this point I'd rather sell plans than give them away. With plans, of course,
you get much more than just schematics. The important part you can figure out from the picture, actually: it's series resonant.
Tim
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User
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I'm really impressed
Can you tell me if in essence this system differs a lot from the one in a kitchen.
What a fine day for chemistry this is.
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12AX7
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How much essence are we talking?
The control circuit is different (e.g., quasi resonant), the inverter is different (e.g., SCR or single IGBT), and the output is different (high
enough impedance to drive directly, plus ferrite pole pieces). It's still the same principle of operation, of course.
The impedance is probably the most important difference. A low impedance can drive a work coil with just a few turns, necessary for the water cooled
tubing high-power heaters need to use. As such, you can heat up steel pipe or frying pans pretty well with a conventional unit, but a stovetop unit
will only work with one work coil driving frying pans. So if you were wondering why a stovetop unit isn't good enough, this is why.
Tim
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watson.fawkes
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The main question I had, then, was whether you are still rolling your own gate drive
circuitry or are using one of the gate drive chips like the IR2113 or TD350?
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hinz
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Looks cool.
Is the big air gap between torroid and induction coil as seen in the picture really necessary?
I always thought that big air gaps decrease the conversion efficiency of transformers. Or does your IGBT burn if there's no more self induction?
Nice big torroid you've got. Could probably build also a badass SMPS for electrolysis with it.
Probably induction heating could be also useful for some high temperature reactions. No need for fancy heating wire, just a well isolated steel vessel
placed inside some coils.
Please upload some plans, especially of the 10kW unit, keep it open source 
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dann2
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Hello,
WOW!
Wondering if it would melt Magnetite. Don't see why not, 1550°C.
Will have to build one of these. They would be a very useful tool in any workshop.
I used to work in a place where they put foil seals (under the cap) on plastic bottles of stuff. It was done with an induction heater. The foil, stuck
to a piece of paper like stuff, comes in the cap . When the cap is tightened the foil is squeezed against the plactic top of the container/bottle. It
then goes under the induction heating head where the foil heats up and melts the plastic of the container top and stick/seals to it.
There were rumours that some guy got a bad burn when he put his hand, with a wedding ring on it, too close the the coil.
Dann2
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12AX7
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The air gap isn't -- since nearly all the flux is enclosed in the toroid, it just matters that the secondary loops through it a few times. That's why
I need a high permeability, ungapped, symmetrical core, exactly what I happen to have.
As a matter of fact, if you put a rectifier and filter on the output of this (instead of the tank), you'd get somewhere around 5.6VDC at up to 120A.
Hope you have big heatsinks on those diodes.
Tim
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Twospoons
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Very nice! Mind if I ask what frequency it operates on? What sort of caps did you use in the resonant tank - they don't look like Celems.
Helicopter: "helico" -> spiral, "pter" -> with wings
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12AX7
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Yes, the bank is 100 x 0.1uF 275VAC MKPs -- unusually small though. They get hot at 3A each! Unfortunately Celem doesn't appear to make a 50kVA
unit, which would be more appropriate here. Their 200kVA product is appropriate for the 10kW model.
Currently, the maximum I can operate at is 300A at 40kHz or so. That puts the work coil around 0.25 ohms, or 75V across it.
Tim
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Vegemeister
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What about putting the capacitive part of the tank on the other side of the transformer? The capacitors wouldn't have to pass as much current, and
the impedance transformation would facilitate a lower operating frequency with the same amount of capacitance.
Edit: whoops, realized part of the idea was free lunch.
[Edited on 7-4-2009 by Vegemeister]
[Edited on 7-4-2009 by Vegemeister]
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12AX7
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Same VARs, just switching amps for volts. Plus now the transformer has to pass all the VARs, making it 10-20 times larger. No thanks.
Tim
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Texium
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Thread Moved
19-11-2023 at 12:26 |
Texium
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Threads Merged
19-11-2023 at 13:07 |
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