Wireless Electricity Transfer (Witricity help)

beenthere

Joined Apr 20, 2004
15,819
There are certain key concepts in this part of their info -
Learn how WiTricity Corp. harnesses highly resonant magnetic coupling to transfer power over distances ranging from centimeters—to several meters.
It is very short range.
 

rjenkins

Joined Nov 6, 2005
1,013
According to the MIT article, the theoretical best efficiency for resonant coupling is 50% and somewhat below that is more practical.

It may be 90% at centimetres while still acting as a transformer, but it won't be practically efficient at significant distances.

Any system like this is basically throwing power in all directions and if a receiver happens to be near enough it will catch a bit of that power, but once out of 'coupled' range the strength decreases by inverse square law.
 

hobbyist

Joined Aug 10, 2008
890
Almost any good designer will start off at small scale, to test the proof of concept, and iron out any bugs, and dthen up the scale, a LITTLE at a time, because undoubtly new bugs will enter in, so everytime you up the scale, tou can fix the bugs by knowing where there at, so once you reach the full scale version, you would have ironed out all the bugs nessasary, to have a SAFE and proper working prototype.
 

Ste_Mulv

Joined Sep 23, 2009
7
I have just had a quick read over these posts and it is a really great idea!

I have been thinking about trying somthing like this myself, but i realised it would be well hard, so I have put it on the to-do shelf that will probably never get done.

I do know that wifi power has been proven to work loads of times, and many companies have tried get a commercial product up and running, however there were of course incompatability issues between manufactures. To solve this some developers (National Instruments, TI, logitec etc) came to gether to create a wifi power standard, that would allow all manufactures to be compaitable with each other. This standard was only created in Q2/Q3 2009, so is very new.

If I were to embark on a project like this one, I would start with that standard, as anything you do build, may as well be intercompatible with future products that will no doubt start to flood the marketplace.

Also if I were to attempt something like this, I would also wait until the creases in the standard have been ironed out. As an example I have used bus communication devices under a couple of standards, and although flexible and widly used the CAN bus standards are too difficult to get inter-compatibilty between manufactures, however the KNX standard is amazing, although not as flexible as CAN, i have seen dis boards with 60+ manufactures all working seemlessly after all being programmed by one single piece of software (ETS professional). If the wifi power consortium are going to be as successful as they hope to be, I reckon they will have to be as tight as the KNX org and that will take a while to acheive.

Good luck though and keep us posted how you get on.

Also, don't go anywhere near any mains voltage! you will get hurt!!!

Ste
 

Thread Starter

zero_coke

Joined Apr 22, 2009
294
Ok I found this:

The MIT researchers successfully demonstrated the ability to power a 60 watt light bulb wirelessly, using two 5-turn copper coils of 60 cm (24 in) diameter, that were 2 m (7 ft) away, at roughly 45% efficiency.The coils were designed to resonate together at 9.9 MHz and were oriented along the same axis. One was connected inductively to a power source, and the other one to a bulb. The setup powered the bulb on, even when the direct line of sight was blocked using a wooden panel.


Allright. I decided to light up an LED instead of a lightbulb, and not use my house power but rather a lower AC power supply.

So heres my new idea:

I think an LED can be lit up at 100 MHz over a distance of 2.5 feet.

I randomly chose those values for these variables, but I want to "tune" the frequency using the dial on the signal generator until I, well, see the LED light up? Then that would be my resonant frequency. I just chose a value for frequency to know what kind of capacitor and inductor to get. Also I chose a value for the capacitor so the only unknown is the inductor (L).

According to the formula,
f = 1/(2*(PI)*LC)

where

f = 150MHz
c = 0.50 uF

100 000 000 Hz = 1 / (2*PI*0.50uF*L)
L = 3.18 mH

We would need an inductor of 3.18 mH.

So our system will consist of a:

Inductor (3.18 mH)
2 x Capacitor (0.5 uF)
Lamp (12V , 60 mA, 0.72 Watts)
And change frequency of AC signal to 100MHz using a Signal/Function Generator

Here's my virtual experimental setup:

 

bigcape

Joined Sep 18, 2009
158
Ok I found this:

The MIT researchers successfully demonstrated the ability to power a 60 watt light bulb wirelessly, using two 5-turn copper coils of 60 cm (24 in) diameter, that were 2 m (7 ft) away, at roughly 45% efficiency.The coils were designed to resonate together at 9.9 MHz and were oriented along the same axis. One was connected inductively to a power source, and the other one to a bulb. The setup powered the bulb on, even when the direct line of sight was blocked using a wooden panel.


Allright. I decided to light up an LED instead of a lightbulb, and not use my house power but rather a lower AC power supply.

So heres my new idea:

I think an LED can be lit up at 100 MHz over a distance of 2.5 feet.

I randomly chose those values for these variables, but I want to "tune" the frequency using the dial on the signal generator until I, well, see the LED light up? Then that would be my resonant frequency. I just chose a value for frequency to know what kind of capacitor and inductor to get. Also I chose a value for the capacitor so the only unknown is the inductor (L).

According to the formula,
f = 1/(2*(PI)*LC)

where

f = 150MHz
c = 0.50 uF

100 000 000 Hz = 1 / (2*PI*0.50uF*L)
L = 3.18 mH

We would need an inductor of 3.18 mH.

So our system will consist of a:

Inductor (3.18 mH)
2 x Capacitor (0.5 uF)
Lamp (12V , 60 mA, 0.72 Watts)
And change frequency of AC signal to 100MHz using a Signal/Function Generator

Here's my virtual experimental setup:

WHOO HOO! NOW THAT SOUNDS LIKE A BAD- @%% EXPERIMENT!

You know the battery charges in my Sonicare toothebrush that way maybe I will take it apart and see how "IT" works!

What are you going to use as the CORE for your coils?
 

rjenkins

Joined Nov 6, 2005
1,013
zero_coke,

you have your formula wrong, it's: F = 1 / (2 * pi * square root( L * C ))
L is in Henries and C in Farads.

Your 0.50 uF + 3.18 mH is actually resonant at about 4KHz.

To use an anything like sensible inductor at 100MHz, the capacitor will likely be in the tens of picofarads range.
 

tibbles

Joined Jun 27, 2008
249
sounds very similar to early radio transmitters /recievers and at the frequencies discussed would be a powerful source of radio interferance, so would need plenty of shielding
also i dont know if its different in canada but the variac does not apparantly provide isolation
good luck with your project
dougal
 

CDRIVE

Joined Jul 1, 2008
2,219
I will readily admit that I didn't bother to do the LC calculation for resonance at 150MHz but I can assure you that the values that you posted are not even close.... Not even a little bit!

BTW, no one is here is going to be surprised or, I quote, "shocked", because most of us know that it ain't gonna happen. Simply believing that you can make something happen will not make it so. If that were true I would flap my arms and fly to work every day. :rolleyes:
 

Thread Starter

zero_coke

Joined Apr 22, 2009
294
I will readily admit that I didn't bother to do the LC calculation for resonance at 150MHz but I can assure you that the values that you posted are not even close.... Not even a little bit!

BTW, no one is here is going to be surprised or, I quote, "shocked", because most of us know that it ain't gonna happen. Simply believing that you can make something happen will not make it so. If that were true I would flap my arms and fly to work every day. :rolleyes:

I am gonna make this thing man. I really don't care about anything. This is gonna happen, one way or another. I will use trial and error and ask questions till I get it.

So whats wrong with my setup? What am I missing?
 

Wendy

Joined Mar 24, 2008
22,800
Several things that I can see. You're transmitter is a series resonant circuit, which can work, but I suspect a parallel resonant circuit would be much more efficient.

The other issue has been mentioned, you're frequency calculations are off by many orders of magnitude.

I encourage experimentation, but you're going to have to climb those learning curves. There is no substitute, what you're trying to do uses multiple disciplines, and your coupling will always be horrendous. You'll probably use 100W to light up a ¼W LED circuit.


Ultimately I suspect (if you persist in these experiments) that you are going to have to build a decent power amplifier to drive your transmitter. Building oscillators is easy, amps are only slightly less so. I doubt you'll find off the shelf equipment to do this.

One last note, the web is a terrific source of info, but there is a lot of disinformation too. Don't be so willing to accept what you read, a lot of it may be true, but there are a lot of scammers and crackpots too. Another reason to climb that learning curve, to be able to distinguish a possible good idea from a crackpot spouting pseudo science. Near as I can tell, the crackpots are winning.

One of my favorite sources is Physorg News, a science site. Here is a recent article you might be interested in.

http://www.physorg.com/news173714272.html
 

CDRIVE

Joined Jul 1, 2008
2,219
No one is saying that this can't be done. Nearly anything can be done with enough power to do the job. Radiated energy is very real thing. When I was a novice ham, who had recently returned from the South East Asia war games, I was living in a small apartment. Obviously, my antenna options were exceedingly limited in that environment. Alas, CQ magazine had a novel indoor antenna scheme that seemed to be just what the doctor ordered. It consisted of a metal room divider pole cut in half and then connected together with a wooden insulator. A large 3" dia coil coupled the two sections of poles and was tapped for operation on different bands. This pole was located within arms reach of my operating position. The antenna was fed from a single length of antenna wire that went to the output of a RC matching network mounted on a 8x8 block of pine. This wire ran under my operating table just inches from my groin! The input from this antenna tuner was 50 RG8 which went to the output jack of my 90W transmitter.

Now that you've got a good idea what the layout was you can see that I was part of the antenna because my proximity put my directly in the field. When I pressed the key down the hair on my arms and on my legs would stand up and I could feel a significant burning sensation on my skin. Current at these frequencies flow predominantly on the skin of the conductor, including biological conductors. It's a miracle that I was able to father children after months of doing this! :rolleyes: That said, the available energy falls of with inversely with square of the distance from the antenna.

If anyone reading this is wondering why my body didn't constantly change the tuning of this antenna as I moved around, I can assure you it did. On the other hand I QSL'd 48 states! :eek:
 

Thread Starter

zero_coke

Joined Apr 22, 2009
294
First off, thank you Bill Marsden. I appreciate your post and the link to the article.

And as to CDRIVE, I have no clue what you just said in your last post here:

No one is saying that this can't be done. Nearly anything can be done with enough power to do the job. Radiated energy is very real thing. When I was a novice ham, who had recently returned from the South East Asia war games, I was living in a small apartment. Obviously, my antenna options were exceedingly limited in that environment. Alas, CQ magazine had a novel indoor antenna scheme that seemed to be just what the doctor ordered. It consisted of a metal room divider pole cut in half and then connected together with a wooden insulator. A large 3" dia coil coupled the two sections of poles and was tapped for operation on different bands. This pole was located within arms reach of my operating position. The antenna was fed from a single length of antenna wire that went to the output of a RC matching network mounted on a 8x8 block of pine. This wire ran under my operating table just inches from my groin! The input from this antenna tuner was 50 RG8 which went to the output jack of my 90W transmitter.

Now that you've got a good idea what the layout was you can see that I was part of the antenna because my proximity put my directly in the field. When I pressed the key down the hair on my arms and on my legs would stand up and I could feel a significant burning sensation on my skin. Current at these frequencies flow predominantly on the skin of the conductor, including biological conductors. It's a miracle that I was able to father children after months of doing this! :rolleyes: That said, the available energy falls of with inversely with square of the distance from the antenna.

If anyone reading this is wondering why my body didn't constantly change the tuning of this antenna as I moved around, I can assure you it did. On the other hand I QSL'd 48 states! :eek:

What are you talking about? Sorry its just confusing.
 
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