Wireless Power Transfer

[Number]

Wireless Power Transfer, Inductive Coupling, Resonant Energy Transfer, or whatever you want to call it, has been a goal of mine for approaching a year now. In order to build this device, I wanted to build and increase my electrical knowledge, in every aspect of the term. The frequency generator I just made (kudos to Kris & Steve) was built specifically for this project.

Goals:
To wirelessly power simple components. This is mainly a project for proof of concept and to provide visual reference that this (Wireless Transfer) can be done.

Details:
According to Cornell College (Reference) they used a signal/function generator (expensive part fyi)
to send a given frequency to a primary coil, which then induces current into a secondary coil. I've tried to list frequencies in videos I have found, but anything appears to work as long as you "tune" the coils to one another.

This is odd because I have not been able to figure out how to find a frequency that works, or the size of coils. I looked at the following information to determine the values of each coil: the frequency, the current through the circuit & coils, and to find out certain tolerances. However there did not appear to be any detailed examples as to how you would tune each coil.

Attempts:
I have tried to mimic the projects found on Google & YouTube but have had little success.This schematic has drawn much attention and seems to be the basis behind most people's projects. It can be viewed Here. I also referenced This Instructable. And many other movies and sites. However these two are the clear winners in my research so far.

Final Thoughts:
My hope is that another person & myself could work together to build this. I am not sure if this project is for my skill level or not; personally I think it is. However just a general breakdown of how to go about this would be most appreciated. Awhile back I did mimic 3 schematics and all 3 have failed. Which is why I am now turning to the community.

This project is what served as my inspiration to get serious about electronics. So it means a great deal to complete this and eventually make changes to increase it, in whatever terms that may be. Learning the principles behind why this works (which I know a majority of) and how to improve it is also a major goal.

So please, if you can, help me out with this thing!

 

[(*steve*)]

The entire problem can be expressed in a single word -- coupling.

You need to look at how the signal generator is coupled to the first coil, then how the two coils are coupled to each other, and finally how the load is coupled to the second coil.

Looking at the first of these, the primary coil must be designed so it has sufficient inductance at the operating frequency to impose a suitable load to the frequency source. This essentially is about the output capabilities of the source, the frequency and the inductance. For the chosen frequency the inductance must be high enough so as not to appear as a short circuit, but also not an open circuit.

Then, the 2 coils must be designed so that the magnetic field from one induces a voltage in the other. The shape, size, core (air?) and distance will all be a factor.

Finally we need to look at the load and ensure the power output from the secondary is suitable for it (e.g. the load appears as neither a short nor an open circuit).

Then, we need to go back to the beginning because loading the second coil will change the behaviour of the first one. It must still represent an appropriate load to the signal generator.

There are no hard and fast rules about exactly what frequency you need or exactly how many turns each coil must be, or how much power you can get out. But you need to find the right balance of all of these.

There are some good examples you might wish to investigate. The one which comes to mind is the rechargeable electric toothbrush. This delivers enough power to a totally sealed toothbrush to charge the batteries inside.

I have fairly recently seen a video of someone taking one of these apart to investigate it -- here.

 

[Number]

Wireless toothbrushes were my first go-to item to dismantle are investigate. Except the base where all the action was taking place was sealed in some kind of resin or epoxy; or both. Assuming coupling is the key factor, which from your explanation it clearly seems so, I wonder what kind of equation ties these together. I did see on WikiPedia an equation for Inductance and for Frequencies, even efficiency, but nothing on coupling. I'm not sure how I would derive that anyways.

Some research into coupling is a good starting place though, I'll be sure to look into that later as the week progresses.

EDIT:
After some additional digging I found some useful information.

Inductive coupling favors low frequency energy sources. High frequency energy sources generally use capacitive coupling.

I'm not sure what context "low" is being described as. Is low considered 1MHz and under, or over? Or some other value. What would your opinion be on this?

 

[Number]

Well holy smokes, I think I found something that will aide in this project.

I do not know if this is 100% correct, so if anyone could verify its validity, that would be most appreciated. It appears like it is correct, but a second opinion never hurts.

Reference

I also came across this, it looks solid as well. I'm not sure if I should use a high or low frequency. Currently my frequency generator goes up to 100 KHz. As before, I do not know if this is a high or low frequency in terms of this project or in real life, where much higher frequencies around in the gigahertz, not kilohertz. Clarification on this would be most appreciated.

EDIT:
It turns out once I got the ball rolling with coupling, the information has just been pouring in. From this website I was able to get and notice certain properties and patterns. Thankfully it all is very straightforward & logical. When I did the calculator on the page I entered in many different values and all increasing in magnitudes of ten or of two. The most beneficial thing to get more inductance seems to be the diameter of the coil. Nothing produced a bigger gain than the diameter did. So I will use an old tidy cats bucket, a good 6-8 inch diameter rounded edge should make a decent coil. Would using thinner wire or thicker wire be better in this instance? My assumption is if the coil is bigger, use bigger wire. Kind of like using the right tool for the job, don't bring a pneumatic drill to fix a screw in the wall, that's overkill. So with that reasoning I think my 14 or 16 gauge magnet wire might be better. :shrug:

 

[CDRIVE]

I don't think I'll ever understand the obsession with this. It's been quite a few years since I read my first post about this on another forum but the whole concept is the antithesis of the current energy conservation craze.

Chris

 

[(*steve*)]

I'm not sure if I should use a high or low frequency. Currently my frequency generator goes up to 100 KHz. As before, I do not know if this is a high or low frequency in terms of this project or in real life, where much higher frequencies around in the gigahertz, not kilohertz. Clarification on this would be most appreciated.

There is good information here that you should read.

EDIT:
It turns out once I got the ball rolling with coupling, the information has just been pouring in. From this website I was able to get and notice certain properties and patterns.

Yeah, all that is assumed in the post I have pointed you to.

 

[Number]

There is good information here that you should read.



Yeah, all that is assumed in the post I have pointed you to.

Thanks for the info. I went HERE and got some information too.

 

[GreenGiant]

I don't think I'll ever understand the obsession with this. It's been quite a few years since I read my first post about this on another forum but the whole concept is the antithesis of the current energy conservation craze.

Chris

Im with you Chris, its cool that you can just toss your device down and charge it, but the potential for ruining things with the large magnetic fields, and the inefficiency of it all just doesnt make sense to me. (though I have heard that wireless charging has got to about 80% efficiency at this point)

There are some cool applications of this technology though, there is a video game out there called "Skylanders" which uses a game pad (called a portal) onto which you place little character figurines, these figurines will light up when places on the plastic pad, and the information about the characters is stored (and read) wirelessly in the figurine, I thought that was pretty cool.

 

[CDRIVE]

Im with you Chris, its cool that you can just toss your device down and charge it, but the potential for ruining things with the large magnetic fields, and the inefficiency of it all just doesnt make sense to me. (though I have heard that wireless charging has got to about 80% efficiency at this point)

It's not the wireless charging technology that I question. The proximity of the primary and secondary coils and the physical construction of a tooth brush charger is made to approximate a transformer as best they can. However, the vast majority of the interest in this technology manifests itself in a pipe dream of grid-less power distribution.

Chris

 

[Number]

Im with you Chris, its cool that you can just toss your device down and charge it, but the potential for ruining things with the large magnetic fields, and the inefficiency of it all just doesnt make sense to me. (though I have heard that wireless charging has got to about 80% efficiency at this point)

There are some cool applications of this technology though, there is a video game out there called "Skylanders" which uses a game pad (called a portal) onto which you place little character figurines, these figurines will light up when places on the plastic pad, and the information about the characters is stored (and read) wirelessly in the figurine, I thought that was pretty cool.

My son is obsessed with Skylanders, and the pad is one of the reasons. I have yet to purchase it, and probably won't, as I think video games are a waste of time, especially for children. But nonetheless, it is fascinating.

The obsession with wireless power is that it's just cool, it's interesting, and there's still room to explore with it. New technologies are always at the forefront of things. It's fascinating, its different, and it goes against how we've used our electronics for decades. Personally I think just lighting a lamp with no wires is very interesting. We all have our 'thing'.

 

[Number]

It's not the wireless charging technology that I question. The proximity of the primary and secondary coils and the physical construction of a tooth brush charger is made to approximate a transformer as best they can. However, the vast majority of the interest in this technology manifests itself in a pipe dream of grid-less power distribution.

Chris

Yeah, I don't find that to be a very feasible idea. I'm just interested in making things light up. Or, do a rehash of those old hockey board games where the little guys went around, almost randomly I might add. Or just to get rid of some cords and free up some space/clutter.

 

[CDRIVE]

I think video games are a waste of time, especially for children.

If they're educational and work their little pea brain a bit they're OK. Not too many of those out there though.

Chris