If it's small amount of power, it's alredy been implemented. If you're talking about transferring megawatts of power wirelessly, then i it has not reach a efficientcy where it is viable.

http://dvice.com/archives/2010/03/rca-supplies-po.php

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Added on March 29, 2010, 12:51 pmbut check out the comments section... very interesthing read, more so interesting than the article.
So do you think this device will decrease the performance of the wifi AP?

This post has been edited by beatlesalbum: Mar 29 2010, 12:51 PM

Wifi signal has probably less than a watt output power. Once it reaches your antenna the amount of power your device can absorb is probably less than 1mW. I don't see how 1mW can charge a battery.

It said 6 hours for full charge.. lets do some calculation shall we?

I guess it using the wave vibration to generate back the current. Any vibration or movement from the wave can generate current to large enough for charging.

Tell me, is there current flowing through air between the up and down steps of a coil transformer?

Simple picture to 'assist' you



This post has been edited by befitozi: Mar 29 2010, 06:57 PM

obviously not.

1mW continuous power can charge a battery albeit over a long time. Boost charger circuits and capacitors are the key to utilizing low voltage/low current power sources. E.g. garden solar powered light usually have a rechargeable battery for storing the power absorbed during the day, and then releasing it during night time. It only powers a small led though.
This won't work for high power equipment e.g. laptop. Nobody is going to buy it if it takes 10 hours to charge up before we can start using it, and only to use it for 5 hours max.


That's one good example of power transfer.
Definition of Power is rate at which work is performed or energy is converted.
Electrical power has a source, then some wires and an electrical load at the end.
Similarly I can have a coal fired steam generator, some insulated pipes to carry the steam and a mechanical load at the end.


So it seems we've discovered 2 aspects to TS question,
1. Just grab power wirelessly from whatever there is out there. E.g. using wifi signals, or one can even harness power from those many power transmission lines that now and then go nears a residential area. Or solar/wind/etc power.
2. The generation and transmission aspect. E.g. if a salesman were to try and sell a generic consumer wireless laptop charger, I would weigh for e.g. how fast can it charge up, how much my electrical bill would be and the effect on my health.

hi, nice pic.

Seriously, u really think a transformer transform the voltages thru "AIR" ??

LOL

What's the iron core for?

Wires with rubber insulators can conduct to the core? Go back to school and learn SPM physics please.

Transformers works with electromagnetic induction. I guess there is no point we discuss this topic with you as you definitely have no idea about Faraday's and Lenz's laws, what more Maxwell's Field equations.

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Added on April 1, 2010, 7:33 pmBack to topic.

I always found this topic to be extremely fascinating.

Anyone thought about transmission through higher dimensional space? Some theories suggest that EM waves are side effects of other phenomena happening in higher dimensions. Maybe if we induce that said effect at the source and have it propagate through such space and reproduce itself at the destination.

Though the physics of this could be solved, what about the engineering of it. Food for thought.

This post has been edited by befitozi: Apr 1 2010, 07:33 PM

To answer the question about the iron core, it is simple to concentrate the electromagnetic flux within the core for more efficient reception of the second coil.

Wow! Good.

So since u know that magnetic flux in the core induces the voltage on the secondary coil, then, y u ask "is there current flowing through air between the up and down steps of a coil transformer"?


A few things to clarify:

Air doesn't play a role in making this a "wireless" transfer of "power".

The iron core is important to "concentrate" the magnetic flux because air is simply inefficient. And the iron core is also made of thin layers of laminated sheet steel to eliminate eddy current (a form of transformer losses because it generates heat - 100% efficient transformer is only theoretical).

So, after all, there is current flowing in the iron core. Power loss is P = I^2 x R

Secondly, it's not called "up & down steps" of a coil transformer. It's called the primary or secondary winding of transformer. In electrical engineering, since there r "step up" & "step down" transformer, the "primary" & "secondary" don't make a good reference (ambiguous). Therefore, it's called the "LV side" & the "HV side".

Thirdly, rubber is not used as insulation for the copper wires. In the industry, PAPER ("Kraft paper") is used for large transformers (say 15MVA 132/33kV) and it is oil-impregnated when immersed in insulating oil (for cooling & insulation purposes). For very small transformer PVC-insulated cables are used. Never rubber.

I guess SPM didnt teach u all that rite?

Thanks.

p/s: Thanks Xerone.

That question and example arose because you insists power transmission requires the use of current. Which is totally wrong.

Eddy currents causes LOSS in power. Are you saying the power loss is the one that is being transmitted? Hahaha.
This example is perfect to show how wrong you are in stating power transmission requires current. Do you even read what you type?


Mind you the low permeability of air is the barrier so it definitely plays a role.

The iron core as Xerone pointed out is to increase it's transfer efficiency but is not a must. We can have a primary winding that coils over a secondary winding with nothing but air in between and it'll still work. The transformer example simply illustrate there's no wired connection between the primary and secondary windings, thus proving power can indeed be transferred "wirelessly".

Again power transmission doesn't necessarily needs electrical current. I've provided an example where power transfer can be done without using nor involving electricity at all in my previous post. So what's wrong with my statement?

Hi,

OK, air has low permeability.

However, quoting wat u said about "air DEFINITELY plays a role". Can u explain how does air play a role in "power transfer" in the transformer? With the characteristic of having low permeability?

For example:

I want to cross over to the other side of the river bank, but there is a huge river separating me and the other side of the river bank.

So... i use a bridge.

But, how does the river play a role for me to cross the bridge?

The river itself is a "barrier" in the first place. Just like air, it is not playing a role because it is a problem that requires a solution.

It is due to the fact that air is a "barrier" that the iron core is used in the first place.

Back to the power & current issue:

(Maybe if we call it TRANSFER of ENERGY, it will be better. It's easier to agree energy can be transfered and converted in many ways, as long as "Conservation of Energy" is observed.)

Now, when there is power, there is a function of current & voltage involved. No matter it is power loss or power transfered or power consumed, power is computed as a function of voltage, current and impedance (Ohm's Law).

The "phenomenon" in the iron core is electromagnetic induction, per se.

What the magnetic flux does is to induce emf in the other side of the windings, causing current to flow when the circuit is connected to a load and thus, power is consumed.

Then, may i ask, how do u compute the amount of power transferred by the magnetic flux?

Bear in mind that what goes on in the iron core, although this is an undesired power loss, is I^2 x R, where I is the eddy current. Although this is power loss, it is also a part of the equation:

Total Input Power = Total Output Power (power consumed at the load) + Total Power Loss (iron & copper).

(Conservation of Energy. Checked.)

Nevermind.

Basically, I get wat u mean. U want to induce lots of magnetic flux (devoid of "current"), then propagate it thru air (wirelessly) and thus cause the receiving end to have electricity (like the transformer).

So, we can somehow use a device to transfer 240Vac supply from 13A socket outlet across the living room to a laptop on the table thru thin air... hmm... ya, i like it too!

But u have said it very well, air has low permeability. So do u still expect power to be transferred via EM wave thru thin air?

Anyway, i do not deny that there may be a possibility someday to make it feasible.

So, what is the next best thing available? Thru current in a conductor, can?

Thanks

This post has been edited by enmavel: Apr 2 2010, 04:01 PM

1. I'm saying air plays a role in wireless transmission. And the reason is low permeability.

2. It's calculated by Faraday's Law. In a complete Maxwell field equation form it is : [curl.E = - d/dt B ] where E is electric field and B is the magnetic field.

3. Of course we can. Except that you will receive only 1nW out of 100W of what you want to transfer

4. Definitely. Maybe you should relook your perspective of what 'air' is. Air is simply space with very very few particles, where as a liquid would have more and solid even more. Of course current can flow through air just extremely inefficient as you said in your first post. Arcing occurs, it is dangerous and massively inefficient. that's why i propose the idea of using higher dimensional space. The concepts of it aren't very new, and certainly isn't fiction either.

5. That's the whole point of this discussion isn't it? .We are trying to find a way to avoid using a solid conductor for obvious physical reasons. On top of that, we are also dismissing the fact that transfer through current is needed. Which you seem to claim that is the best way to do so. Clearly not, else Nikola Tesla would have ruled the world with his inventions.

This post has been edited by befitozi: Apr 2 2010, 04:19 PM

Hi,

Thinking in this direction, if the exterior of a house is being wound with a large coil and subjected to induced electromagnetic field, and all the electrical equipment in the house has built-in "secondary" windings, that can in turn, induce emf and VOILA! ... "wireless" power transfer!

But conducting objects will be heated up too... like the pot on the induction cooker.

Therefore in practice, induced EM field is what ppl is trying to avoid. if 2 conductors r placed side by side, with only 1 carrying current, the 2nd conductor will also have induced current flowing due to the induced magnetic field. (that's y 3-phase power cables are arranged in trefoil formation)

Then other appliances will also need very good insulation, because EM is also a source of "noise", especially in AV equipment....

i do not know if human body is OK with such exposure too...

Is this wat we want to do "wirelessly"?

For the sake of discussion, some suggestions in the following analogy, for the fun of it:

let's say i have a large water reservoir on top of a hill. i want to supply water to the village downhill but i do not want to use water pipes.

Maybe i can do it "pipeless" by allowing the water to evaporate and become clouds. The clouds will then drift to the village and become rain. Villagers can then collect the rain water for their daily use.

Or,

Maybe i can freeze the water into sizable ice cubes/balls etc. then roll it down hill for the villagers to collect and thaw into water to use.

Or,

Transport the water bucket by bucket to the village by trucks.

I think wat we need to consider are:

a) safety
b efficiency
c) feasibility

thanks

1. Radio waves are EM too. As long as it is below UV frequency it should be fine

2. Similar to the idea i said about higher dimensions. Using a different medium not in direct contact with our physical world

3. Similar to laser/photonic transmission. Very promising field imo.

This post has been edited by befitozi: Apr 2 2010, 05:01 PM

I am not sure but, if we do want to use the same transformer principles to excite the secondary coil installed in some electronic device without the need for a medium, shouldn't the change in EM field be at a sufficiently high frequency? Would keeping it at radio wave frequencies work?

I don't think we should look into magnetism as a solution. I used it merely as an example to show that current is not necessary to transmit power.

But another field where magnetism should be explored extensively is magnetic levitation. but that's a whole new topic all together