I've heard about smartphones that support wireless charging. For me it's an amazing miracle!! I googled and found out that it uses something like a transformer for a wireless charging. I had another question because a transformer have an iron core and the two coils ( primary and secondary ) should be very close to transfer power between them... so I wondered how to get rid of the iron core and achieve long distance ? I searched again and I read about radio communications that uses "Resonance" to achieve long distance without using a magnetic core.
I have another question and that I don't find its answer, Radio communications transmit very small power. I think it is few micro volts because we use amplifiers to receive it ... so How can a charger send very large power to a smart phone through long distance and without magnetic core ?
Can I make a homemade device like that ? For example, I connect a homemade coil to an AC supply (low power) Then, I connect another coil to an LED. When I the coil is connected to the power, The LED is on ?

Thanks in advance, and sorry about my english

 

The reason we use an iron core in a transformer is to improve the coupling between primary and secondary. It is possible to build an air core transformer. As you move the primary and secondary coils further apart the coupling becomes weaker and weaker. In short it is not possible to "send very large power to a smart phone through long distance...". You might find the following article interesting.

http://en.wikipedia.org/wiki/Permeability_(electromagnetism)

 

How can a charger send very large power to a smart phone through long distance and without magnetic core ?

It can not do that.

 

The reality is that the separation distance for effective inductive charging will remain quite small.
I have an electric toothbrush working on the same principle. Nothing particularly earth shattering about the concept.
To claim that the principle works sufficiently well to "send very large power to a smart phone through long distance" is an exaggeration, to say the least.
Next thing, someone will be claiming a device has been invented which can charge a smart phone by harvesting radiated power from other nearby smartphones. Then presumably, we'll have to download an expensive app which is claimed to stop this happening to our phone.

 

It can not do that.

At least you didn't yell by using all capital letters

 

At least you didn't yell by using all capital letters

I thought maybe he has a vision problem.

 

It can not do that.

But I want to do it, so it must be possible. You are just trying to annoy me by not telling me how it can be done.

 

The guy you need to talk to is Nikola Tesla who unfortunately passed away back in 1943, he had a good handle on how to do this. On a much smaller scale my electric toothbrush uses induction coupling to charge the battery. I think Tesla was a forum member here but I can't find any of his old notes.

Ron

 

I'm not a native English speaker what I meant by "a very large power" is about 3.7 volts / 1200 mAh which is the power of a cell phone battery. I said "very large" because I was comparing it with the power of radio waves.

Also, "long distance" is about 1 meter. I was comparing it with the distance between the two coils of a transformer.

t_n_k said: "I have an electric toothbrush working on the same principle"
I assume that the distance between the toothbrush and it's charger is 1 meter long or a little bit less. If it is, toothbrush's coil and charger's coil should transfer power that is similar to the power of radio waves because long distance makes magnetic field weaker. Moreover, the coupling between them is not improved because there is no iron core as Papabravo said.
That's why I think the power transferred between them is probably weak but practically, It is not weak. It is able to make toothbrush ( or a cell phone ) work..so would you tell me how the power is improved ? the only way I know is to make the two coils like a transformer (putting them too close with iron core).
You are too funny #12 I laughed too much when I saw your answer feel free to write in small font, I don't have a vision problem, I don't even wear glasses

 

I'm not a native English speaker what I meant by "a very large power" is about 3.7 volts / 1200 mAh which is the power of a cell phone battery. I said "very large" because I was comparing it with the power of radio waves.

Also, "long distance" is about 1 meter. I was comparing it with the distance between the two coils of a transformer.

t_n_k said: "I have an electric toothbrush working on the same principle"
I assume that the distance between the toothbrush and it's charger is 1 meter long or a little bit less. If it is, toothbrush's coil and charger's coil should transfer power that is similar to the power of radio waves because long distance makes magnetic field weaker. Moreover, the coupling between them is not improved because there is no iron core as Papabravo said.
That's why I think the power transferred between them is probably weak but practically, It is not weak. It is able to make toothbrush ( or a cell phone ) work..so would you tell me how the power is improved ? the only way I know is to make the two coils like a transformer (putting them too close with iron core).
You are too funny #12 I laughed too much when I saw your answer feel free to write in small font, I don't have a vision problem, I don't even wear glasses

1 meter is a very long distance. The guys who build the charging mats where you set the phone on a plastic charger (without plugging it in) have trouble with efficiency. That is about 2.5mm. So, yes, charging at 1000 mm is a very long distance.

And, if it were something that could simply be answered by a "how do I do this" on a forum, don't you think every battery powered toy and cell phone would have Ben powered by this etherial wireless energy for the past 20 years or more?

Read the bold print above.

 

they are very inefficient and waste power,
have a look here,

http://m.instructables.com/id/Low-Power-Wireless-Charging/


http://www.electronicshub.org/wp-co.../Wireless-Battery-Charger-Circuit-Diagram.jpg

 

The guy you need to talk to is Nikola Tesla who unfortunately passed away back in 1943, he had a good handle on how to do this. On a much smaller scale my electric toothbrush uses induction coupling to charge the battery. I think Tesla was a forum member here but I can't find any of his old notes.

Ron

He wrote them in the margins of his library books -

 

Now I understand, Thank you all for your useful answers,

 

they are very inefficient and waste power,
have a look here,

http://m.instructables.com/id/Low-Power-Wireless-Charging/


http://www.electronicshub.org/wp-co.../Wireless-Battery-Charger-Circuit-Diagram.jpg

They also have to be very carefully designed, or they'd wreak havoc with radio reception, wi-fi signals, bluetooth, etc...

 

I believe it can be done if only there was a way the direct the magnetic flux. For light we have lenses, so for magnetic field surely there could be a method to focus the magnetic flux to a region or along a beam. But with present know-how, it would be an inefficient exercise.

 

Just to update, present technology gives hope to direct magnetic flux to a point/beam. check the links below:

Apparatus and method for amplifying a magnetic beam
http://www.google.com/patents/US5929732


Explosively pumped flux compression generator
http://en.wikipedia.org/wiki/Explosively_pumped_flux_compression_generator

So long distance wireless charging is possible in the near future.

 

Here is a working prototype from some university for charging electric vehicles:
http://www.pes.ee.ethz.ch/uploads/tx_ethpublications/20_Accurate_Finite-Element_Bosshard.pdf
5kW power transfer, 95% efficiency, 5cm distance
The remaining piece of ferrite core helps for better coupling (and system performance and/or efficiency), but is not principally needed.

 

I believe it can be done if only there was a way the direct the magnetic flux. For light we have lenses, so for magnetic field surely there could be a method to focus the magnetic flux to a region or along a beam. But with present know-how, it would be an inefficient exercise.

Among the problems faced is for example cost. Unless something becomes cost feasible it simply isn't worth doing.

Ron

 

transformers can be iron core, ferite core, air core or even two wires run paralell to each other. people forget that any two wires can cross couple hum, noise, emi, or what ever just by having any changing current flowing through it and another conductor near.