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Andy

Mon Sept 09 2013, 03:11AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Hi

If I run a induction furnace off 60 car battery's Would you alot have 10 in series 6 in parallel or 5 in series and 11 in parallel. If the work coil has ten turns would 5 volt be enough or to low a value.

If its amps that does the heating, what would be the minimum voltage that you could use for the work piece, say if you've got 345volts with 100 turns primary would 3.4volts be to low?

Thanks

Andy

Tue Sept 10 2013, 09:14AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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I was planning on building this circuit, should be ordering the parts this Friday, was wondering if there was anything I'm missing.
After a quick test was thinking in paralleling 4 car battery's.

Ash Small

Tue Sept 10 2013, 11:10AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I assume this is a question about manufacturing ferrite.

I don't think the sintering process requires the ferrite to melt, it just fuses at high temperature.

Various carbonate pre-cursors are used. They are heated and CO2 is driven off. This 'ferrite' is then ground into powder ~1 micron in diameter, then the powder is re-sintered. The size is important, but I can't remember the term used to describe the phenomena. Something like 'single magnetic domain', or something.

I did hear recently that ferrites are an excellent 'waveguide' for microwaves, so it may be possible to sinter it in a microwave oven.

EDIT: "Ferrites are produced by heating an mixture of finely-powdered precursors pressed into a mold. During the heating process, calcination of carbonates occurs:
MCO3 â†’ MO + CO2
The oxides of barium and strontium are typically supplied as their carbonates, BaCO3 or SrCO3. The resulting mixture of oxides undergoes sintering. Sintering is a high temperature process similar to the firing of ceramic ware.

Afterwards, the cooled product is milled to particles smaller than 2 Âµm, small enough that each particle consists of a single magnetic domain. Next the powder is pressed into a shape, dried, and re-sintered. The shaping may be performed in an external magnetic field, in order to achieve a preferred orientation of the particles (anisotropy).

Small and geometrically easy shapes may be produced with dry pressing. However, in such a process small particles may agglomerate and lead to poorer magnetic properties compared to the wet pressing process. Direct calcination and sintering without re-milling is possible as well but leads to poor magnetic properties.

Electromagnets are pre-sintered as well (pre-reaction), milled and pressed. However, the sintering takes place in a specific atmosphere, for instance one with an oxygen shortage. The chemical composition and especially the structure vary strongly between the precursor and the sintered product.

To allow efficient stacking of product in the furnace during sintering and prevent parts sticking together, many manufacturers separate ware using ceramic powder separator sheets. These sheets are available in various materials such as alumina, zirconia and magnesia. They are also available in fine medium and coarse particle sizes. By matching the material and particle size to the ware being sintered, surface damage and contamination can be reduced while maximizing furnace loading."

EDIT: "Single domain, in magnetism, refers to the state of a ferromagnet[1] in which the magnetization does not vary across the magnet. A magnetic particle that stays in a single domain state for all magnetic fields is called a single domain particle (but other definitions are possible; see below).[2] Such particles are very small (generally below a micrometre in diameter). They are also very important in a lot of applications because they have a high coercivity. They are the main source of hardness in hard magnets, the carriers of magnetic memory in tape drives, and the best recorders of the ancient Earth's magnetic field (see paleomagnetism)."

Andy

Tue Sept 10 2013, 06:32PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Hi Ash Small

Thanks for the info it might come in hand later, but I don't have a use for the furnace at present. I'm just trying to reach the 1700C mark.
I read that tungsten has a melting point of 3500C, what temperature does oxidation occur as google isn't helpful. To minimize the heat loss was planning on running it in a low vacuum but iron oxide if it melts will give off oxygen.

Andy

Wed Sept 11 2013, 04:09AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Will start by building this, should get the parts by Monday
Will plan to have 20 transformers 10 per voltage direction, to give 500volt, with a 5-10 turn work coil. 4 car battery(60Ah) in series times 4 in parallel for 240Ah at 50volt, should give about 1 hour run time before they need recharging.
How many amps can a circuit board handle, how do you lot wire up 20amp transistor

EDIT
Thanks IamSmooth,

so I need to make the circuit get into resonance to make the work coil have the resistance of the wire, I've tried adding cap to the circuit but the amps is max of 880mA....more reading

Edit
Using the formulas for black body radiation loss (P = e*a*A*T(4)), e of 0.5 tungsten,and a crucible size of 0.5meters round by 0.3meters high to reach a temperature of 1973Kelvin I'll need 202kw. At 600volt and 400 amp there should be room for losses. Will need 500 battery's for 30mins or 250 battery's for 15mins.
At 0.3*0.3meters need 121kw, 150 battery's for 15mins
At 0.3*0.1meters need 40kw, 50 battery's, which might be doable

Working out the even and odds of turns and stuff, for 600volt, 80 amp, 9 turns should give the most power, with 0.1ohms resistance of the iron oxide with a copper wire trace.

Andy

Sun Sept 15 2013, 11:55PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Yah Christmas has arrived :) , have tested the setup, I get 6.46 volts across the FET, at 50% duty cycle, but the transformer was a MOT core with 5 turns, and the volts just register. How come the volts is so low?. With 30 turns its 2.23 volts, but thats with one lead not connected.

EDIT
Being searching and built a h-bridge, the voltage doubled , was wondering how to make the square wave more sine? as I think it only passes the change in voltage of a second(/45ns). Will it work at more power as a induction furnace, or do you need a sine wave?
Any one?

Tried with a ferrite core, 10 by 10 turns, getting 1.64 volt

Tried to make a sine, just need to wound a 10mH transformer

EDIT
MY bad, the values of the resistor were to high, replaced r1 with 100ohms and r2 with 5kohms and 5nF, its topping 8.25volt at 28khz :)

Andy

Fri Sept 20 2013, 02:33AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

I'm asking for a quote for this pcb from a supplier, but was wondering how would you lot build this, pcb or some other way

Thanks

Just trying to workout how much heat is lost from a crucible in a high vacuum, the black body formula I think is if air is surround the crucible?

Just bounce a idea off you lot, but if the calcium silicate with a low thermal covers a large area in kw radiated, the crucible will heat up more, say if you have enough CS that its 200kw and the crucible 120kw, the crucible will heat upto 200kw with a 120kw input. The number are optimistic?

Ash Small

Fri Sept 20 2013, 08:32AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Well, if the yellow areas are copper traces, and the green is insulator, you could cut copper sheet to those sizes, and bolt or glue it on.

Andy

Fri Sept 20 2013, 06:38PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Hi Ash Small
Thanks, didn't think of that :facepalm: .Found a suppler that might cut them aswell. Can you run FETs in parallel, have the same setup as above, but 20 FETs in place of one.

Ash Small

Fri Sept 20 2013, 09:11PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Andy wrote ...

Can you run FETs in parallel, have the same setup as above, but 20 FETs in place of one.

Yes, but read the application notes on the subject first.

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