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Miniature wireless power demonstrator

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LAN_403

mister_rf

Mon May 07 2012, 10:16PM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

There was no relay at that time and the circuit was triggered by using a simple switch, but later I had to use one in order to simplify the start-up procedure.

About the capacitor, there are actually two pieces hidden there (close to the power supply terminal blocks), see the picture:

1336428716 4465 FT74096 Capacitor Test Wireless

Monir

Wed May 09 2012, 02:57PM

Registered Member #3680 Joined: Wed Feb 09 2011, 12:48PM
Location: Porto Alegre - RS - Brasil
Posts: 3

Hello Mister_rf

Thank for help me!

Did you try to simulate the circuit in a software?
Is this C7 the little gray capacitor, isn't?

[]'s

Tue Jun 05 2012, 12:10PM

Registered Member #4750 Joined: Sat May 05 2012, 02:29PM
Location:
Posts: 1

Hello everybody,

My native language is not English, so I apologize for my mistake

Primarily, Marko, I want to say thank you very much for this project. I'm electrical & electronics engineering student. I made this project, wireless energy transfer, for my electromagnetic field theory lesson and I attached these photos. Transmitter circuit frequency is approximate 1 Mhz and I measured 15-20 cm transfer distance. Maybe in the future I would like to promote this project. Thanks everybody and Marko.

Best regards.

Crozatti

Sat Aug 25 2012, 03:30PM

Registered Member #4752 Joined: Sat May 05 2012, 07:00PM
Location:
Posts: 2

Hey guys,

First of all, thanks for Marko for this great project, it really works and it's very detailed making the possibility for a layman like me construct the project. Thanks!

Now, I'm going to step 2, construct the wireless mobile charger, with the help of the detailed post of mister_rf.

Thanks for all guys, you're really great!

wops

Thu Nov 08 2012, 10:49PM

Registered Member #7846 Joined: Sun Nov 04 2012, 06:59PM
Location:
Posts: 1

Hello everyone,

First thank you all very much for posting and sharing your knowledge about wireless energy it is really nice to get so much informations from one thread !! Thank you especially marko for all your work.

I'm trying to make your circuit, the one with the new PCB, I can't wait for my components to arrive because I'm really excited to start the experiments !

One question though, I tried to make a simulation of the circuit on LT SPICE IV, it seemed that it worked but my question is, does it fit reality and especially what you saw during your experiment ?

Here are the circuit on lt spice, and the current in the inductor L3 from the tank

One more question, how did you chose the value of the choke ? why 100micro and not more or less ?

thanks !

--
Wops

Sulaiman

Fri Nov 09 2012, 01:31PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

MISTER RF .... is that really how you connected the relay?
I would expect the gate drive on before the dc to the inductor(s).

Crozatti

Sat Dec 08 2012, 07:29PM

Registered Member #4752 Joined: Sat May 05 2012, 07:00PM
Location:
Posts: 2

Hi guys,

I finished my project with a junction of marko and mister_rf schamatics, and the results is charger a phone over 25cm with full power.
I believe that is a great result, but, I have a little and important doubt...

How I calculate the inductance of inductive magnetic coupling? I mean, the "antenna"?
Can anyone help me?

Thank you

zero_coke

Fri Mar 08 2013, 05:22AM

Registered Member #8368 Joined: Wed Nov 28 2012, 04:11AM
Location:
Posts: 9

Hi Marko,

Great experiment! I have a few questions of my own if you could please answer:

1) We are planning on using separate modules do the oscillating and power amplification. How come you are using a Royer Oscillator instead of using a signal generator + a Power Amplifier? I understand Power Amplifiers are lossy but class E and class F oscillators work well in high frequencies and are efficient. Can you tell me why please.

2) When I'm out looking for capacitors, what ratings should I be looking for? I noticed you used the WIMA FKP1 series and about 8 of them in parallel. Is the reason you have 8 because you want to distribute the power amongst the capacitors? If so, what ratings of voltage should I get them in and how many should I use?

3) When you were pumping out ~20A into your coil, did you measure the H and E field around your coil? I'm asking this because safety standards dictate a maximum field strength of ~5 A/m from 0-1MHz and about ~5/f from 1-10 MHz where f is in MHz. I'm wondering because this sort of limits how much current you can pump out into your driving coil. We calculated a maximum current of 2.8A for our coils to be below this field strength. Can you please verify this.

4) Is there an advantage in using a 4 coil system whereby your transmitting coil is inductively coupled to your source coil? I noticed some people did this and it improves their resonator Q and increases the overall efficiency of the system but I don't know exactly why. I know that by having an extra coil in the middle you can refer impedances back and forth depending on the # of turns you have setup but when these coils are so far apart can you even refer the impedance of your load coils which are like 30cm+ away from your transmitter to your primary coil? I don't think things work like the transformer action way at such low coupling. I dont know if the formula exists for referring impedances with non-unity coupling coefficient values.

5) Thanks man :)

Marko

Sat Mar 09 2013, 01:18PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hello everyone! Glad to see so many people still being interested in this project that dates from my high school days. I'm now actually approaching the end of my college studies and am having only less and less time to teach about things like these. However I have some time right now so I'll try to answer a few good questions here.

zero_coke:

1. - It's absolutely possible to use a fixed frequency signal source and a class E or similar amplifier to feed the transmitting circuit, and could easily be more efficient than the Royer oscillator (especially the crappy version presented in this thread, I haven't been using that for a long time now!). However, the fixed signal source would mean you now have two degrees of tuning instead of one which greatly complicates the tuning process. If your system is moved around or intended to be used in a serious application the resonant frequencies of the resonators will certainly change and you'd have to readjust both the resonators mutually, as well as the signal source. Royer oscillator always drives the transmitting resonator at resonance, so only one degree of tuning is necessary. Bonus for you if you can make the receiver self-tuning too!

For any serious application, I'd make sure that at least the primary side is self resonant no matter what topology is used. For really high power I'd probably favor a series resonant half bridge class DE amplifier with PLL or similar feedback. However, one must note another advantage of royer oscillator - unlike most other topologies, it always keeps the tank circuit voltage constant. Series resonant on the other hand would ring up without load and would need an extra control loop to prevent it from blowing itself up if it's Q is allowed to go too high.

2. I used 8 parallel capacitors to distribute the fairly heavy tank current among them. For a higher power design the number of capacitors could easily get impractical - in this case it would be a good idea to switch towards conduction cooled capacitors such as used for induction heating.
In royer oscillator, the capacitors see pi*supply voltage peak. I used overrated 1000V caps to get more surface area for cooling, and because I had them at hand after all.

3.Well, I don't have any equipment that I can use to accurately measure H at RF frequencies - though inside the coil it can be estimated as H = I/D where D is diameter of the loop... so in this case its about 200A/m for a 10cm coil. I figured any such rules are silly, so I ignored them; induction heaters can produce 2-3 orders of magnitude greater H in vicinity of their coils and yet no laws seem to prevent them from being produced and used. You can't do anything about laws of physics here!

I'd only be concerned that stray radiation that could disrupt radio communications, so I'd probably chose some ISM band frequency like 6.775, 13.55 Mhz or such. Note that is a double edged blade, as it would enable your wireless transmitter to resonate and fry some RFID and radio devices operating at these frequencies. So you might just chose a frequency low enough to assure that your system doesn't get to radiate significant power as radio waves.

4. "4 coil" system is really nothing but a method of feeding power into and out of resonators. You could also do it directly by series or parallel feeding, as well as use a ferrite transformer for insulation if necessary. If your resonators are Tesla coils they become such high impedance that it's practical to feed power by capacitive means as well!

You're probably referring to MIT experiment where resonators were free coils that had single loop coils near them to feed power in and out. The resonators likely had kilovolts on them and were rather impractical to be fed directly by a vacuum tube oscillator, or to drive a light bulb directly, so the air core step-up and step-down transformers were required.

On the other hand, I loaded my single-turn copper loop with a big capacitor which makes it's impedance so low that it can transfer fun amounts of power with as little as 50V input.

Q of the resonators doesn't really have much to do with this - it's all about losses in copper and capacitor dielectric in the resonator (if capacitors are present, of course).

Marko

zero_coke

Sat Mar 09 2013, 08:41PM

Registered Member #8368 Joined: Wed Nov 28 2012, 04:11AM
Location:
Posts: 9

You are awesome man! Thanks for taking the time to answer the questions. I have some pictures to show you and a few more questions if you have the time please.

First is the signal generator we bought to generate a signal at some particular frequency:
https://www.dropbox.com/s/wprrxo55gxjzfuu/oscillator%20-%20top%20view.jpg

Next is the pre-stage amplifier (5W output) needed to drive our main amplifier:
https://www.dropbox.com/s/skcmh1s361oui2y/pre-amplifier%20-%20top%20view.jpg

And finally this is our main amplifier (140W):
https://www.dropbox.com/s/t7paoiugywegm4d/amplifier%20-%20top%20view.jpg?

And then we have our coils which are 1 turn, 10 turns, 10 turns, and 1 turn, respectively. The first two coils are inductively coupled which is on the transmitting end and the last two are inductively coupled on the receiving end. The middle two are resonant coupled. The first two coils are copper pipe, and the last two coils are just copper wire (not thin wire or anything, just a

I have a few questions now that I'd like to ask:

1 - We couldn't find any reason to pick a high frequency or low frequency for our resonant frequency for this application. According to our simulations it seems like lower frequencies give better performance in terms of power input and power output, but I'm still not convinced as to why even though the numbers dictate. Wouldn't using higher frequencies be more efficient? I always thought that operating at higher frequencies would increase efficiency of the system.

2 - I noticed that you said you had 1 capacitor in the transmitting end. Can you tell me again why you had just 1 instead of multiple capacitors?

3 - Can you please tell me again how the resonant frequency will change in my setup as compared to the royer oscillator setup? So are you saying that by moving the receiver closer/away from the transmitter I will need to re-adjust my resonant frequency? I just need a little more explaining if you don't mind sorry. I don't know why the resonant frequency will change if I move the receiver. By the way, our load is going to be either a light bulb or a fan so that might not be a problem in this setup would it?

4 - Do we need to match the output impedance of our amplifier to the coils? I mean, the amplifier is rated for 140W into a 50 Ohm load, so do we need to make sure that the coil at its resonant frequency has an impedance of 50 Ohms? I'm assuming if you have this setup, maximum power will be delivered to the driving coil right? What if our coil does not have 50 Ohms, do we just add a series resistor to match it?

5 -Do you have any recommendation for us? Right now we have a signal generator connected to an amplifier and that amplifier is connected to our main driving coil. It's basically as simple as that. We're hoping that with about 100W input into our main transmitting coil, we can get about 20-30W at the output. Does this seem feasible to you?

Thanks very much Marko and friends!

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