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Induction cooker to battery charger conversion? Answered

Just an idea at this stage, but what, apart from the usual safety, would stop us from using and iduction cooker for wireless transfer of electricity?
Am I missing something or is the only thing preventing the cooker from running with a coil instead of a pot the right coupling?

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Downunder35m
Downunder35m

12 months ago

Ok, seems induction cookers are not desinged for insane operators :(
Used the salvaged parts from another cooker to make a receiver coil with the usual series capacitor layout.
As the coil was firmly glued onto the ferrite strips anyway I did not bother to change it or to replace it with strips matching the size of those in the working cooker.
The receiver coil had 4 turns more than the sending one but at least the capacitors matched - ready to produce some science smoke ;)
Sadly the connected 1000W halogen tube did not cope with the about 750W the cooker was set to.
It was insanely bright and before I could shut all off it blew the filament.
My multimeter is said to accept 750V AC but showed just an overload sign :(
Should have known better..
Recitfied AC in a switch mode resonant coil configuration resluts in way over 1000V going through the coil...
But hey, why think before if smoke helps you to have some science fun?
A 2000W iron that I rarely use on my clothes should to the trick if set to max heat and I let it steam off ...
Well, it did sort of...
To my utter suprise the cooker kept sending juice until I got a distance of about 3cm between the coils.
Until then there was no noticable loss of heating or steam but at the max distance the cooker just shuts off.

Now I am getting courious....
Creating a nice self oscillating and resonant circuit for a induction cooker coil isn't too hard.
If in doubt my own circuit and a beefy power supply will do just fine here.
The ferrite bars are to make sure the magentic field is not wasted on the underside and of course to provide a much higher flux density for the system - the pot provides the same shortcut for the magnetic field lines.
Going back to normal magnets, we know that the potted ring magnets are very good for your fridge and things like that.
You get almost twice the holding power for a few cents of added metal around the magnet.
Similar can be done with an electromagnet by using a multi coil configuration.
You can even choke the field lines through a tiny hole - similar to our old analog TV sets.
To explain it an oversimplyfied way imagine a set of stacked ring magnets with gaps between them but all orientated the same direction.
The field lines between would go straight from one to the next instead of going around the originating magnet.
Same works for coils...

Why wouldn't it be possible to create an inductive coil antenna?
A Yaki antenna with coils instead of radiating elements.
The reflector would be the ferrite strips, the active element the coil from the cooker.
Each follwoing element with the right spacing for the frequency get smaller for the inner and outer diameter.
Always a bifilar coil with series capacitors set to the same resonant frequency.
In theory this should create a very narrow outlet for the magnetic flux.
And with enough elements we would create a very long "magnet" that is very strong.
If theory would come close to reality I would guesstimate that a 5 coil array would be able to transmit about 80% of the energy coming from the driven element at a distance of up to 80-100cm.
The receiving coil would have to be matched in size to the field and with a matching geometry to utilise the field lines according to their density.
We know we can not reflect magnetic field lines, we can only offer them constrictions or easier pathways.
But about paramagnetic materials like bimuth?
I wonder if anyone ever experimented with bimuth alloys for the application in high frequency electromagnitc applications...
And further more:
If we already use ferrite bars to direct the field lines on the underside of the coil, what would happen if someone has a faulty 4 "burner" induction cooker with fried electronics only?
How hard would it be to create cylindrical, coil with all the spare ferrite bars as a core??
If the inductivity can be properly matched the cooker would know any different but we a magnetic field that is now focussed onto very, very small area....
No clue if the ferrite would hold up to the task without overheating and how many bars are required to cater for the max of 2100W but I guess there is only one way to find out...
Guess I better start with an induction heating circuit on 50V before misusing my cooker again....
Imagine you would machine the ferrite bars to form a nice cylinder with a length to match the frequency - wouldn't that make it a quite powerful antenna?

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Jack A Lopez
Jack A Lopez

12 months ago

I think that will work, as long as your receiving coil, or the assembly containing this coil, does not contain any ferromagnetic materials, like steel for example.

The reason why is because I think steel gets heated anisotropically. I mean it gets heated no matter what its orientation with respect to the work coil.

But it is different for ordinary conductors like copper or zinc. Those need to be oriented, kind of in the same direction as the currents in the work coil.

Or at least that is what I have observed, by experimenting with a homemade induction heater.

I think this circuit I was using was authored by someone with the handle Uzzors2k.

http://uzzors2k.4hv.org/

Although the funny thing is, I have also read in your posts that you invented this circuit, and it was stolen the next day by Chinese reverse-engineers, and turned into a direct-to-eBay product.

Anyway, regarding my experiments with this homemade induction heater...

A piece of steel would turn orange hot, even if it was long and skinny, and oriented at right angles to the turns of the work coil.

In contrast a penny, an American one cent piece made of zinc with a thin copper shell, in a glass test tube, would feel a torque that would stand it on end. This was with the work coil pointed up.

I mean the turns of the work coil were winding around the vector that is up (or down) in my laboratory. I mean the interior space of the work coil resembled a "hole in the floor", and I could hold sample materials above that hole, or drop them down in it.

In contrast, the coil axis could be turned sideways, perpendicular to gravity, like a "hole in a wall." However doing that way, there is danger of molten liquids dripping onto the turns of the work coil. With the axis of the coil pointed up, like a hole in the floor, gravity pulls liquids straight down, through the hole in the center.

Where I am going with this story, is to get that penny to actually melt into liquid zinc, I had to sort of weigh it down, with some small pieces of ceramic, to keep it oriented with its "turns" oriented parallel to the turns of the work coil, in spite of the torque trying to turn it sideways.

Experiments with single loops of copper wire were similar. Those loops would absorb significantly more power, e.g. glow with incandescence and melt, when oriented parallel to the turns of the work coil, but just get warm when oriented at right angles to the work coil.

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Downunder35m
Downunder35m

Reply 12 months ago

You just can't help yourself, can you? ;)
I ask for one thing and you come with another just to make me try it out LOL
At least for once I have a slight head start here.

I did some tests with the coils from a big oven top.
Despite having different sized markings on the glas top, the coils used seem all to be identical, except the one for the biggest pot.
Anyway, I wanted to see if energy transfer is actually possible, so I decided to use a few loops of wire and some X2 rated capacitors to make a test coil.
Tried to get close to the resonant frequency of the work coil and used the standard QI aproach with two capacitors in series.
Needless to say that someone frgo that the QI standard means power handling is applied - a thing my cooker had no clue about...
Took quite a few connected lamps to make the cooker run and lights go on.
For a few seconds until my wire loop burnt out with lots of smoke LOL
Anyway, I got curious and triedthings like coins and small metal plates.
Not always easy to trick the cooker to stay on...

I think it is th same eddy currents that make a metal cylinder spin next to an electromagnet fed with AC - like the old electricity meters with the spinning dis.
Since we are dealing with high frequency RF th skin effect comes to mind for things like coins.
And it is always easier to magentise through the greatest distance instead going from top to bottom in a coin.

My problem right now is that I can not crank the cooker down below about 900W.
Anything lower and it just shuts off :(
Makes it a bit hard to use as a battery charger unless you have a few big trucks or battery shed for your solar system.
Bit of overkill for my car and motorbike.
Too bad that these cookers take the short and easy way out when it comes to the inner workings :(
Maybe I should go back to converting it to a half decent induction melting furnace instead...
If there just wouldn't be the problem of coupling and curie temperatures :(