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Induction heater project

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eskoilola:
Last time I visited home back in finland I did some brazing. Brazing is actually quite easy but to achieve the needed temperature with a butane torch took quite some time. During this time the otherwise nice component got an layer of oxidation on top of it. Not nice. Further more that is an open fire and it can be somewhat hazardous in my small shop. Doing this outside is a no-go when the weather is rainy or there is a lot of wind. So I decided to start a project that I am capable of completing.




So here is the first part of this project. It is a chinese 1.8kW induction warmer device. Funnily enough - these guys have strictly prohibited .... whatever that is - it does not say. Quite many hobbyists have fried these devices as they do not know that the power should NOT be connected gradually. There should actually be a PHYSICAL switch or really fast switching FET array to cut on/off the power to this device. It should be directly in the DC line. This is because the construction is such that it needs a "kick" to start oscillating. A mechanical switch with the contacts bouncing and creating a lot of ripple before they settle is actually a perfect solution to this problem. It can also be a relay. A fet array might work but it generates only one pulse which might not be enough to get this going. If the power is applied gradually the output FETs of this device will blow skyhigh. I have suitable transformer (2 x 24V 2000W) and a pair of suitable filtering capacitors (100.000uF/63V) along with the needed rectifier components. Should not be a problem.




The overall construction is OK-ish but some details are just too flimsy for that kind of power. This needs new connectors for the output coil. Connecting kiloamperes using long brass nuts is nuts. At those current levels those warm up and dissipate the power in a place where it should not be dissipated. I will probably use 1 mm thick copper "foil" on top of the PCB traces where needed and on the output use some tube adaptors which have their counterparts silver soldered on the output coil. This allows for easy coolant flow and way better connection for the output resonance circuit.




Other than that the construction seems to be quite nice. The blowers are needed to cool down the output FETs and the output tank circuit capacitors. It will be seen whether I need to change those to some real quality stuff. This kind of a circuit generates currents in excess of kiloamperes and that will fry any not-good-quality capacitor. Luckily I have some suitable capacitors back home. If I would need to buy those it would cost more than this device - including the postage.




The supplied output coil is flimsy. Pushing 1.8 kilowatts through that one will create losses like anything else. I will visit the local (local in finland) hardware store and get copper tube that is more to the job. This tube is actually a joke with 5 millimeter diameter and 0.7millimeter wall thickness.




Another item I purchased for this project is a water pump. This one is up to the task. It is a really good quality and can make the cooland really go around. 11 liters per minute with 0.5atm pressure. Quite impressive for such a small device. It states that the pump must not be run dry and that the polarity of the wires should net be changed. It is a brushless motor the pump propeller being the motor rotor itself. Water is used as a lubricant and coolant for the motor. Therefore no dry run. I probably need to direct part of the yield directly back to the radiator to allow more flow for the pump. Let's see how that goes.




So today I ordered the radiator for this project. It is a oil cooler for racing applications. Very tough device. The one I ordered has a cooling area 75x115 millimeters. the actual area is a lot bigger as the cooler is quite thick and there are a lot of cooling fins between the coolant tubes. This was quite affordable as it has strange 3/8 BSP threads. 55 degrees of thread angle ... LOL. It will be fun tho fabricate fittings for this one. Hopefully the threads are not left-handed .... The actual page in eBay is HERE




Last but not least I paid a visit to the saturdaily flea market. Today there was this Noga deburrer which had a very affordable price of 50 eurocents. The blade is long gone. Ordered a set of new blades from USA (the chinese are cheaper but they take forever to arrive). This tool is probably of the very first versions ever made by Noga. It has an aluminium shaft and it is still as good as new - if You forget the blade.

awemawson:
I'll be watching this thread with interest.  :thumbup:

I decommissioned my 100KW induction furnace when I moved here 11 years ago, and it is still in the fireproof space I built specially for it gathering dust  :palm:

It's a big rack on castors about 1 meter square and 1.8 tall driving a crucible 'furnace body' that looks like a cement mixer. I have two - one that tilts and pours the metal, the other inverts and the mould gets clamped to the top so the melt is never exposed.

In addition it has a 15 kw cooler to chill the water that is pumped though the coils

It was because of this device I had a 160 amp per phase 415 volt feed brought in ! (previously I used a diesel generator)

eskoilola:
Yes. I also somewhat believe that the turnout of this one might be interesting for those that want to do some hot stuff but do not have the correct (fireproof) setup for that. With induction heater the energy goes (is supposed to go) exactly where needed without setting the cardboard boxes around on fire.

One thing I need to rhink over is the electrical isolation of the coil. I have seen some pictures of coils having a fiberglass sleeve but I do not feel comfortable with that solution. I would rather mold the coil in some fireproof cement, alumina maybe,  in a way that the the coil is free to move outside that ceramic. I have some coil formers that might be suitable. Those are made of some really tough ceramics ... but I have the faintest idea whether those will survive the temperatures. One option is to get a readily formed alumina tube - another option is to make it myself - I have to renovate our garden grill anyway so why not make it of some impressive material. The quantities one must buy the castable alumina are not small.....

awemawson:
When I rebuilt mine I had to have crucibles made to order from one of the (then) newly escaped Russian satellite countries - wasn't too pricey - I had a dozen made and ten are still on the shelf. They are totally embedded and not removable without chipping them out. Oddly I had some spam from the firm today which I deleted so I can't look back and see who they are !

PK:

--- Quote ---So I decided to start a project that I am capable of completing.
--- End quote ---
That's classic me...

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