Hi All,

interesting discussion.

however, a few basic things we need to know:

1) Electricity consists of:

a) Voltage - Potential difference between 2 points
b) Current - the flow of energy (electron flows at the opposite direction - current was discovered/established b4 electron)
c) Impedance - the resistance to the current flow in a medium

Comparing to water:

Water at the reservoir high above the hills has potential energy. Water flows downward to a lower area thru water pipes. The size of the water pipes determine the amount of water flowing thru it. Can we transfer water without pipes? Maybe in the future?

2) In order for electricity to flow, we need a medium or "conductor" (the "pipes"). Without the pipe, water will get splashed everywhere & some areas might be flooded & ppl drowned (hazard!). Same with electricity.

3) While conductor is used for transfer of current (i wont refer to electron on sub-atomic level), we need insulator to protect the surrounding from getting electrical shock and flash-over. Short-circuit is a fault that is not desired in electrical system. it is similar to water leakage in the pipes.

4) Air is an insulator. If current flows thru air, it's an "arc". Arcing occurs when very high current flows thru the conductor and it ionized the air and caused the dielectric (insulator) breakdown. it will find the closest path to ground/earth/another conducting path to complete the circuit. This is similar to lightning phenomenon.



In practice, we do not want "arcing" to occur because this is electrical hazard. Very high current is flowing thru and a lot of heat is generated.

While i cannot foresee the future (anything is possible), at the time being, electricity must be channeled thru a conductor and protected by insulators.

Electricity is different from data transfer.

Thanks.

I LOLed at the "Power transfer doesn't means we need to use electrical current".

I guess there is nothing more i can say until u read about P=IV

I rest my case. hva nice day.

hi, nice pic.

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

LOL

What's the iron core for?

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.

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

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

Hi,

Thanks 4 the definition.

Now we are talking about "electricity" rite? So, i'm talking in the context of electrical power. If u take wat i said about power involving current out of the context....

Tun Abdullah Badawi "transferred power" to DS Najib - NO CURRENT INVOLVED ("wireless" too )

OK, U WIN


Solar "Power" or Solar "Energy"?

Can we decide a term to be used amicably here? Well, I have said in my reply to Senior Member befitozi:




OK, let's look at SOLAR ENERGY:



So, we can see the nuclear fusion gives out energy.

This energy is transferred to earth, and the "light" that we receive during daytime is from photons.

(The cycle starts with the thermal collision of two protons (1H + 1H) to form a deuteron (2H), with the simultaneous creation of a positron (e+) and a neutrino (v). The positron very quickly encounters a free electron (e-) in the sun and both particles annihilate, their mass energy appearing as two gamma-ray photons) Nuclear Fusion

It is this energy that we "harvest" at the photovoltaic cells:

This energy causes the photovoltaic to emit electrons and this electron causes current flow, which in a complete circuit connected to load, gives us power.

So, i dun call it solar power when it's not yet realized as "power"... while it's still in the transfer process as "energy".

Another story:

Money gives us "buying power" & i must earn money 2buy something.

U can say u dun need to involve "money transaction" to buy something (by barter trade )

Money, is like current, it flows from 1 party to another, giving the person having it "buying power"....

So, I plant durian in my orchard (sun).

Passers-by asked: 'What r u doing?"
Me: I'm planting "buying power"
Passers-by: ???

So, during durian season (nuclear fusion), i collected my durian & transport to pasar malam to sell.
Passers-by: Wat r u doing?
Me: I'm transferring my "buying power" to pasar malam
Passers-by: ???

So i sold my durian (photon) & i got money (current) & now i have "buying power"... I can buy 10 nasi lemak for my family

OK, sorry. Went to far off the track LOL



May i ask something...

Touch n' Go cards, u need to touch it rite? The "reader" reads the info in the microchips via RF.

Those SmartTAG, (active RFID) has battery & thus it transmit the signal back to the reader via RF.

Err.. RF... = power transfer?

Nevermind.

Guys, interesting discussion here. No hard feelings OK?

Topic: Transfers power wirelessly, Wifi, 3G. can electricity did that too? (Science)

The definition of power is RATE of Energy Transfer.

Power dun "exist" while energy is converted from 1 state to another. It is a measure of rate: how fast work is done.

If I push a box, I'm transferring energy to the box, overcoming friction and cause it to move (kinetic energy).

How fast i perform the work (rate), is a measure of the amount of power i have.

If i can push a box for 1 m in 1 sec and u do it in 2 sec, i'm more "powerful" than u. (example only )

I do not transfer POWER to the box.

Secondly, when u pay for electricity, u r paying for ENERGY = kWh transferred to your house. Not for "POWER" transferred to your house.

Since ur avatar looks like wikipedia , here u go: Electrical Energy

kthanxbai