High Efficient wireless power transfer

[Akmalidin]

I have been working on the wireless energy transfer recently.Therefore, I am having low efficiency.I have set several coils with different parameters.Could anybody suggest any method to increase the efficiency?I want to transmit high voltage with high efficiency about 50-70W. I have tried with 25 V in source and got max 5 V in receiver coil,the current received was 3 mA when I supplied 1A .The distance is 25 cmAnother question that bothers me is , even though coils reach resonant frequencies they are not transmitting high voltage and current.Why?

 

[anorlunda]

How much power are you trying to transmit?

What have you tried?

What are your results?

We can't help you without more detail.

 

[Akmalidin]

I have edited the post.please read and give me suggestions.
Thank you

 

[anorlunda]

How much distance between the coils?

 

[Akmalidin]

The distance is 25 cm

 

[anorlunda]

Have you studied transformer design? Is sounds like you are building a transformer, even if your don't realize it.

 

[Akmalidin]

yes I have studied and my goal is also building the step up transformer.what could you suggest?

 

[anorlunda]

Good for you. The simplest, most efficient step up I know is an autotransformer. But thst might not meet your other requirements such as wireless or isolation. You should really make up your mind what you're trying to achieve first. I suggest searching the threads in this forum. Several threads discuss homemade transformers.

Perhaps someone else can recommend a textbook or an online forum for this OP.

 

[anorlunda]

I am in the middle of Lake Okeechobee at the moment, so my Internet bandwidth is near zero. But a search for "making a transformer" on YouTube brought up some hits. (It also brought up numerous videos on kids transformers toys)

 

[Akmalidin]

thank you

 

[jim hardy]

you'll find this site interesting

http://amasci.com/tesla/tmistk.html

TESLA'S BIG MISTAKE?
William Beaty Sept 1999LINKS

While experimenting with a long, thin 'secondary' coil from a Tesla Coil, I suddenly connected up several things in my mind which had been separate up to that moment. After years of messing with Tesla Coils, I finally see what Tesla was up to with single wire transmission, with resonant coils, and with longitudinal waves. See if the following doesn't make sense...

 

[Akmalidin]

First of all, thank you for the information ,I found it really interesting and generated in me some doubts that I have never thought of.In this experiments, impedance matching was not mentioned.Is the matching of impedance really important?

 

[jim hardy]

impedance matching was not mentioned.Is the matching of impedance really important?

third paragraph:

If we choose the correct value of load resistor for the "receive" coil, then all of the electromagnetic energy flowing along the long thin secondary will be absorbed by the receive coil without reflecting.

as with any transmission line

 

[Akmalidin]

I got the point.But I just want to clarify the reason why we need it.Is it because of, If we have the same impedance, We will have the same resonant frequency? And that is why it is preferable to deploy twin coils to get high efficiency as they resonate in the same frequency?

 

[jim hardy]

Resistance will absorb energy. Reactance won't.

The right amount of resistance will absorb all the incoming energy, any other value will reflect some of it.

Remember, a resonant circuit appears resistive because X_L.and X_C are equal and oppposite.

 

[Akmalidin]

As the right resistance value provides high absorbing, Could you please tell me how to determine the right resistance value?

 

[Akmalidin]

But I thought, resistance dissipates the energy ,how can it adsorb? and what is the benefit of that absorption?

 

[jim hardy]

I think you'll have to build one and experiment.

Your device involves transmission line basics, as mentioned by Beatty in that article.

here's a very abbreviated introduction.
http://afni.nimh.nih.gov/sscc/staff/rwcox/ISMRM_2006/Syllabus%202006%20-%203340/files/H_03.pdf

But I thought, resistance dissipates the energy ,how can it adsorb? and what is the benefit of that absorption?

energy enters the resistor as electrical and comes out as thermal.

 

[NascentOxygen]

I have been working on the wireless energy transfer recently.Therefore, I am having low efficiency.I have set several coils with different parameters.Could anybody suggest any method to increase the efficiency?

Are you doing this at mains frequency, 50/60 Hz? Are the coils placed inside one another, or end to end? Are you using an iron or ferrite core?

 

[Akmalidin]

I am using resonant frequency not 50/60 HZ.the coils are separated with distance 25 cm. I am not using either iron or ferrite core as my coils are separated.

 

[Mike_In_Plano]

The concept of "mutual inductance" means everything when analyzing this problem. At 25cm, the mutual inductance will be very low for small diameter coils. Even with large diameters, the mutual inductance is low.

The circuit requires high primary currents typically with a parallel capacitance to generate high circulating currents. The secondary also requires capacitance, to tune out leakage inductance seen by the receiving coil.

 

[NascentOxygen]

I am using resonant frequency not 50/60 HZ.the coils are separated with distance 25 cm. I am not using either iron or ferrite core as my coils are separated.

How are you energizing the coil? Approximately what is the frequency you're using?

25 cm is way too far apart. You could use cores; a separation of 0.5 mm still counts as "wireless" (without a direct connecting wire).

 

[anorlunda]

The OP never told us what he is trying to accomplish, nor what he defines as efficient. Therefore, all our speculations regarding what is "better" could be off the mark.

An induction phone charger, and a radio transmitter plus remote receiver, both fit the definition of wireless power transfer.

 

[Akmalidin]

sorry for making all this things obscure .The frequency i use is 500kHZ as the coils are resonating.The impedance matching dramatically increased the results but however, still i did not get really good efficiency.The input voltage is 25V and 1.5A.I want to have in the output as least 16V and 0.5A.So what could improve my results?

 

[NascentOxygen]

You insist on having the coils 25cm apart? Would it be acceptable to have a cylindrical ferrite core spanning that gap, so both coils were on the same core? You could slide one coil off the core when you needed to separate them.

A transformer with a removable secondary winding...

 

[Akmalidin]

yes I would like to keep the distance.i don't think it is acceptable to deploy the cylindrical ferrite core as I don't want anything to be present in between coils.

 

[anorlunda]

Akmalidin, what are you trying to accomplish?

 

[Akmalidin]

As I mentioned I want to have really good efficiency to charge my phone !

 

[NascentOxygen]

As I mentioned I want to have really good efficiency to charge my phone !

For high $\eta$ over a 25cm span you need microwave dishes.