Induction heater for graphite

[Rachie5272]

I'm doing some science experiments, and I'm looking for an induction heater.  I intend to heat small 2-3 mm diameter graphite rods to 200-300 °C as quickly as possible.  Does anyone have any experience with these cheap ebay units?

I suspect I won't need anywhere near a kilowatt, but I can water cool it just in case.  How do I control something like this?  PWM the power supply?

[AF6LJ]

You might be surprised how much power it does take.
Here is the experience of one person who used the same one you linked to.

[Someone]

Resistive heating of the graphite is used in some processes., why do you want induction?

[miguelvp]

Resistive heating of the graphite is used in some processes., why do you want induction?

maybe some cold heat soldering iron implementation?

[rikkitikkitavi]

Graphite has quite high resistivity, relativivly seen and  therefore it will be difficult to induce sufficient currents for heating an object made from graphite.

Skin depth is high, so it will heat evenly though.

I would rather look into resistance heating by current.

You control it by controlling the frequency, it is a resonant converter.

[Ian.M]

"The center lead is obviously the gate."

Never seen any center-base or center-gate devices in TO247, ever.

+1.  Its almost invariably the substrate of the die and electrically connected to the thermal pad so you can bet its *NOT* the base/gate without even looking at the datasheet.

[AF6LJ]

"The center lead is obviously the gate."

Never seen any center-base or center-gate devices in TO247, ever.

+1.  Its almost invariably the substrate of the die and electrically connected to the thermal pad so you can bet its *NOT* the base/gate without even looking at the datasheet.

Indeed.

[SeanB]

If you are willing to pay for the specialised new punch set for the leadframe, and are willing to order 100k of parts, pretty much any manufacturer of power semiconductors will make you a custom leadframe, with the leads in any order, so long as it conforms to a JEDEC outline, and if you want to pay more they will make them non conformal to that as well. The centre substrate leadframe is just a convention, it can really be any one of the leads, using the right punch tool to stamp out the copper alloy sheet used in manufacture.

[Rachie5272]

I want inductive heating for two reasons: not having to touch the graphite with electrodes, and being able to heat only a small section at a time.  I'm working with thin but very long pieces of graphite, and need to move the heater along the length to stimulate a chemical reaction.

I originally thought of using hot air, but induction seems so elegant, and can be done in a vacuum.

[SeanB]

Doing zone refining then.

[Rachie5272]

Yes, that's an apt description.  I'm not working anywhere near the melting point of carbon, but I want the reaction to proceed in a similar manner.

So, does anyone know of a cheap induction heater which won't explode when first turned on?  I can't quite afford a $1000 unit for a proof of concept until we get more funding.

[calexanian]

Some thoughts about induction heating graphite. First graphite is a good material for induction heating. It actually heats very well. We heat 2 inch by 2 inch cylindrical anodes in high voltage rectifier tubes to red heat regularly in production. Zone heating as you are mentioning is hard to control however due to the high radiation factor of graphite.  if you are heating small pieces of consistent dimensions I would just build my own unit for heating or investigate those hand held both heater units. You can send the company a sample and specs for how hot you want the piece and they will make a cool to suit.

[JoeN]

You might be surprised how much power it does take.
Here is the experience of one person who used the same one you linked to.

Holy cow, who is this guy?  What is his deal?

[AF6LJ]

You might be surprised how much power it does take.
Here is the experience of one person who used the same one you linked to.

Holy cow, who is this guy?  What is his deal?

https://www.youtube.com/channel/UChWv6Pn_zP0rI6lgGt3MyfA
He is funny.

[T3sl4co1l]

Off the shelf?

There are few options.  Induction heating below 1kW is not useful, so I don't know of any real products.  There is a wand type device for automotive purposes http://www.theinductor.com/ but it's above 1kW, and I think near or above $1000, too.

Your only other choice is to build it yourself, or buy one of those silly toy circuits.  Same thing, really, as a proper induction heater circuit needs frequency tracking, control and feedback, and protection circuits, and those take time.  Anything you'd throw together would be just a toy.  (So, hey, if you have the parts on hand, you might as well make something basic, instead of waiting for delivery.)

The other problem is frequency.  A few mm graphite rod probably won't heat very quickly for frequencies under 100kHz.  Most toys aren't intended to run that fast.  So you'll probably be building it yourself, but also having trouble dealing with stray inductance, burning transistors, etc... 

For power control, you'd probably just vary the supply voltage/current into one of these things, yeah.

Tim

[JoeN]

He is funny.

I was wondering if anyone who watched his channel knew what his overall bio is.  Is he an engineer, tech, scientist (not likely, right?), or just a self-taught bubba?  Why does he do his channel?  Anyone know?  I will watch a few of his other vids but I wondered if anyone had a one-sentence summary in advance.  I'm not sure I like his shtick or not, still up in the air on that, but he seems to know what he's talking about.

[LaserSteve]

Perhaps get a OEM Fluxeon board and pay Neon John to optimize a coil for your load?

http://www.fluxeon.com/buyflux/index.php?route=product/product&path=33&product_id=52
Steve

[calexanian]

You might be able to get enough power out of an 807 tube in a driven oscillator configuration and a output air transformer to heat it. I suspect you will be in the few mhz range for such a small diameter object to heat. 

[calexanian]

Wait wait wait. WHy bother with induction for such a small mass at such a low temp. Just wrap a loop of nichrome loosely around it and heat it up. What would heat up the rod pretty fast. 

[ajb]

He is funny.

I was wondering if anyone who watched his channel knew what his overall bio is.  Is he an engineer, tech, scientist (not likely, right?), or just a self-taught bubba?

I think he's some sort of heavy equipment mechanic or similar, he's made references to spending weeks at a time fixing equipment in middle-of-nowhere mining operations.  He's definitely sharper on the mechanical side of things than the electronics, but he does a lot of fun projects and his tool reviews involve ripping the subject to bits in an informative and entertaining manner.

[dkozel]

Check out this guy's setup. The video description has the full parts list.

[Rachie5272]

I was searching around for cheap induction heaters again, then realized the Metcal soldering iron I use is just that.  I think I'll try making a new coil, and see if it will heat the graphite.  It even uses a standard DIN plug.

I have no idea how the driver will respond, but it shouldn't be any worse than potentially melting the coil, right?

[T3sl4co1l]

Well... blowing up the power supply is always an option.  Somehow I doubt the user manual says what range of SWR it's safe to operate into...

Tim

[AF6LJ]

I was searching around for cheap induction heaters again, then realized the Metcal soldering iron I use is just that.  I think I'll try making a new coil, and see if it will heat the graphite.  It even uses a standard DIN plug.

I have no idea how the driver will respond, but it shouldn't be any worse than potentially melting the coil, right?

I think I would advise against that.

[vk6zgo]

You could always forget induction & use an Oxy/acetylene torch or a blacksmith's forge!