# Wireless Electricity Transfer (Witricity help)

#### zero_coke

Joined Apr 22, 2009
294
zero coke,

To make a matching pair of tuned LC circuits, you need to figure the frequency (fr) you want the circuit to resonate at. From that fr you can determine capacitor and inductor values. One of the elements should be variable, in order to easily 'tune' the circuit. Then build both circuits and then them up!

I would recommend getting some kind of simulation software (pspice) and simulating your design first. That way, you can play with the values easily double-check your math, and (most importantly ) not waste any money on wrong parts.

How you actually measure stuff depends on what kind of test equipment you have. If you have a good oscilloscope, and a function generator, you can look at the input and output signals of the circuit. Remember a resonant circuit also behaves as a filter, passing your desired frequency and rejecting others. So if you can supply various input frequencies and observe the output, and if your circuit is correct, you will see that the magnitude of the output is much smaller than the input, except when near the resonant frequency.
Okay, so regarding the L, C, and Frequency values I don't know how to calculate them. I know the formula is:

But I don't know the L or C values to calculate the resonant frequency.

Regarding the SPICE software, I find it difficult to use becasue it seems like its a programming language on its own and I really don't want to branch off learning other things because I don't have the time...its command line but its sort of hard for complex circuits...

And what do you mean by measuring input/output frequencies? How do you measure these? And sorry again but can you tell me what you mean by the input will be much smaller than the output? Is this our goal?

So -SK- I did what you said and I drew this diagram so please let me know if I'm missing something o have something wrong:

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#### -SK-

Joined Apr 14, 2009
25
Ok, I can see that your understanding of circuit design is quite limited. I'm not trying to 'put you down', but once again this is a serious complex project that you are trying to jump into. You need to learn alot more before you proceed with this.
I really don't want to branch off learning other things because I don't have the time...its command line but its sort of hard for complex circuits...
If you don't want to learn, this will never work for you. The best way to learn about these circuits is to simulate them and observe their behavior. For example, if you simulate the circuit you show in the picture you will see that it will not work as you want it to.

http://www.linear.com/designtools/software/ltspice.jsp

This is a free spice program you can try. I use Orcad PSpice, I'm sure there are many other versions. Microcap is another free simulation program. The version I use, and Microcap, and others, are graphical programs. You drag and drop components onto the schematic, connect them up, and run the sim. It is fairly simple to get into, and there are loads of tutorials out there to help you out.

Start by simulating some of the examples shown in the 'textbook' sections of this site. Once you figure out how to use the software, simulate your input stage, aka the parallel resonant circuit. Try a variety of resonant frequencies with different L and C values and observe the DC and AC behavior of the circuits. The formula is there for you to calculate the missing pieces when at least one is known. So for example, pick a resonant frequency, pick a capacitance, and you can solve for what inductance you need.

Once you can do that, you can come up with an idea of what circuit you need in the real world. Also, your questions about the circuit's operation will be answered by performing a simulation. Then we'll get to the next part.

#### zero_coke

Joined Apr 22, 2009
294
That's really awesome -SK-. I'm still learning and I've been doing quite a bit of reading on circuits. I'm currently reading the entire textbook on this site, and I'm on page 250 of 1000, so I got more to read. Thank you very much for your help throughout. I will try the simulation programs and then play around with it.

#### zero_coke

Joined Apr 22, 2009
294
Man how in the world do you use these freakin softwares? I just want to draw a simple battery connected to an LED and it's like rocket science to do it...these people never take into account the human factor seriously.

Are there any simple SPICE simulators out there? I tried LTSpice, it was probably the most complicated thing to use in the world. Then I tried MicroCAP, and forget the usage, I couldn't even install the damn thing. I have to pretty much hack the registry and use some russian made keygen and use the HASPemul whatever program to find HEX codes and then use these codes during installation of the software....I can't imagine the usage....aaargh!!

I tried OrCAD PSpice, and I install the program and there is like 10 different programs, and none are the ones I can actually use to make circuits and simulate them. Seriously is it just me or are these softwares made only and ONLY for extreme experts in circuit design and theory?

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#### CDRIVE

Joined Jul 1, 2008
2,219
Well yes, they're not written for neophytes. Here's TINA that's free from Texas Instruments.

#### -SK-

Joined Apr 14, 2009
25
I know orcad has lots of random programs in it. The one you want is the schematic capture program. On different versions it is called ' Capture CIS', 'Schematic Capture', or just 'Capture'. To simulate stuff, there is a button along the top toolbar called 'simulation profile' or 'edit simulation profile' or something like that. Click on that to set up your sim parameters. I don't remember microcap that well, and I'm not as familiar with other programs, but I can give a few pointers for orcad.

Here are a couple of basic tutorials I found:
http://www.ee.siue.edu/~gengel/pdf/PSPICEtutorial.pdf

#### zero_coke

Joined Apr 22, 2009
294
Well yes, they're not written for neophytes. Here's TINA that's free from Texas Instruments.
Is this one supposed to be easier to use or another one of the 'others'? Anyways, I'll download it and try it. Thanks.

And -SK-, I have two programs that match what you said:

There's CAPTURE Student and SCHEMATICS as two different programs out of the 15 programs installed. Which one is it?

EDIT: Nevermind, I started reading the tutorial you posted and got it. Thanks

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#### CDRIVE

Joined Jul 1, 2008
2,219
Is this one supposed to be easier to use or another one of the 'others'? Anyways, I'll download it and try it. Thanks.
Well I think it's easy to use and quite intuitive too. Actually the free version is a stripped down version of the commercial version that I have, but it's more that usable. I used the free version prior to purchasing the Classic Suite version.

#### zero_coke

Joined Apr 22, 2009
294
Okay so I tried the programs and I am not able to use them since they're very complicated...Now I'm just going back to internet research to build this thing...

So -SK- can you tell me why my current design won't work? I think the only thing I'm missing is a signal generator to find the resonant frequency and once I find that it should work , right? I mean, here's the pic again for your convenience:

#### zero_coke

Joined Apr 22, 2009
294
Anyone? I need some help in setting this up please. So I need to make a LC circuit, an inductor attached to a capacitor. On the receiving end, an inductor and a light bulb. Is this right?

#### thingmaker3

Joined May 16, 2005
5,083
So -SK- can you tell me why my current design won't work?
Coupling efficiency is reduced in proportion to the square of the distance between coils. Try 0.5cm or 0.05cm instead of 50cm.

Also try a either a much higher frequency or much larger coils. Try adding iron or ferrite cores to the coils.

#### THE_RB

Joined Feb 11, 2008
5,438
Hey Zero, it looks a lot like the little air couple transformers they sue to charge electric toothbrushes. Maybe do a google search for "hacking electric toothbrush" etc.

The one I looked inside was powered from 4v ac and the coil was a few hundred turns total about 1.25 inches diameter. A smaller coil in the toothbrush base was slightly less diameter and turns.

It charged a AA size NiCd battery over a few hours so I'm thinking thats plenty enough to light a led for your experiment.

PS. You dont need the capacitor on the coil, it will operate at mains frequency you dont need to try to make it into a resonant circuit. What you do need is HEAPS of turns of very fine wire and close distances.

#### zero_coke

Joined Apr 22, 2009
294
Thanks guys. But I'm not trying to make something sort of to a transformer...it looks similar but this is wireless electricity transfer over a good distance, say a couple feet. In a transformer or those toothbrushes you are talking about, they have very very minimal distances, and in a transformer the two coils are so close it is almost neglible distance. What I'm trying to do is light up a lightbulb from a couple feet, or I will try lol.

So the trick has to do with the frequency of the transmitting coil, and since for electromagnetic induction to happen there needs to be a pulse or alternating of curent, which is why I'll use AC and use a capacitor to charge and discharge so it will induce current into the second coil, at a specific resonant frequency doh.

What kind of coil should I use? I saw the people at MIT used a 20 inch coil of around 10 turns, and its thickness was about 1-2 cm. I have the same coil, but I think I need to set up an LC circuit, and attach a function generator set at 10 MHz and see if it will work.

Any ideas on why this won't work?

#### CDRIVE

Joined Jul 1, 2008
2,219
What I'm trying to do is light up a lightbulb from a couple feet, or I will try lol......

What kind of coil should I use? I saw the people at MIT used a 20 inch coil of around 10 turns, and its thickness was about 1-2 cm. I have the same coil, but I think I need to set up an LC circuit, and attach a function generator set at 10 MHz and see if it will work.
Since this is destined to be forever known as the thread that refuses to die, perhaps you can tell us what the wattage of the lamp that they used was and what the output wattage from their source was? This is just a wild guess on my part, but I'm betting this lab experiment had a power transfer efficiency in the negative range! One thing I'm sure of is; you don't own a function generator that is going to approach the power you will need even for a wimpy fractional wattage lamp!

#### zero_coke

Joined Apr 22, 2009
294
Since this is destined to be forever known as the thread that refuses to die, perhaps you can tell us what the wattage of the lamp that they used was and what the output wattage from their source was? This is just a wild guess on my part, but I'm betting this lab experiment had a power transfer efficiency in the negative range! One thing I'm sure of is; you don't own a function generator that is going to approach the power you will need even for a wimpy fractional wattage lamp!
Ok. Listen. All they did was light up a standard 60W light bulb, 7 feet away. I'm sure a standard function generator ($300) is sufficient to do this. I need a schematic on doing this...I'm reading on LC circuits but still, not enough... #### CDRIVE Joined Jul 1, 2008 2,219 Ok. Listen. All they did was light up a standard 60W light bulb, 7 feet away. I'm sure a standard function generator ($300) is sufficient to do this. ...
Yeah, 60W function generators are about as common as Hens Teeth!
If you're going to persist in this endeavor it might behoove you to set your sights a bit lower.... like a fractional wattage lamp.

#### bigcape

Joined Sep 18, 2009
158
The core problem is you are depending entirely on inductance to restrict current flow. This would be reasonable if you had a 1000 turns on the primary coil, but 10 turns? The house could burn down. Go to the AAC book and read up on inductors. Your primary was probably in the neighborhood of 0.01µH, with a reactance of an ohm or so. Not good, very bad.

So this is how my cordless/waterproof SoniCare toothebrush charges with NO electrical contacts when it sits in its cradle?

Everything should charge its batteries this way!

#### rjenkins

Joined Nov 6, 2005
1,013
In that article, they mention an efficiency of 15%

That means to get 60W out, they are putting 400W in, and that is no doubt after a lot of optimisation of their setup.

You need a very serious RF amp to get that type of power, not a function generator.

Also note the lamp is not connected to the large resonator coil, there is a smaller matching coil driving the lamp - the text states the lamp is inductvely coupled to the receiving coil.

This means there is no resistive load on the resonator coils so they are extremely high Q to get even that power efficiency.

Looking at the size, turns and turn spacing of the resonator coils, I'd say they are self-resonant at around 10MHz without additional loading capacitors. Notice the bits of packing in the top of the coil - it appears the turn spacing has been 'tweaked' to get exactly the required frequency.

#### lostcowboy

Joined Sep 20, 2009
2