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Miniature wireless power demonstrator

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ARB

Sat Aug 31 2013, 06:35AM

Registered Member #27139 Joined: Wed Jul 03 2013, 06:16PM
Location:
Posts: 3

Greetings to everybody.

First of all, I would like to thank Marko for his circuit.

I am studying in the university and in order to apply to the degree of Bachelor in Electronic Engineering I am making a thesis about Wireless Power Transmission. Marko's circuit (the non-SMD version) was helping me as a first insight into the matter. I am trying to modify it, first by substituing the resistor divider to the gates by an optocoupler with a separate 12V source, but for some reason it doesn't work yet.

I would like to ask Marko (if possible) a couple of things: How do you obtain the aproximation that the peak voltage of the resonant LC parallel tank is pi times the DC supply voltage, and how can you estimate the RF current circulating by the MOSFETs? I tried to look in every book available at my faculty, but in every one of them they analize parallel resonant circuits with a current source and not a voltage one, so I can't figure how to apply the theory in this case.

My goal at the end is to, at least, attain charging a cellphone or tablet (5 - 10 W) with a distance of a couple of meters. If you could help me to achieve that, I would be truly thankful.

jechwa

Sat Aug 31 2013, 12:12PM

Registered Member #33559 Joined: Wed Aug 28 2013, 01:43PM
Location:
Posts: 5

ARB wrote ...

How do you obtain the aproximation that the peak voltage of the resonant LC parallel tank is pi times the DC supply voltage

My goal at the end is to, at least, attain charging a cellphone or tablet (5 - 10 W) with a distance of a couple of meters. If you could help me to achieve that, I would be truly thankful.

you find some useful equations here. The page is in german but I think you understand the equations at the bottom:
http://www.mikrocontroller.net/articles/Royer_Converter

You want to transmit wireless power over a distance of meters? You need extremely large
coils!!! Look to my videos. I found a method to increase the distance. At the moment I can
trasmit over a distance seven times the diameter of the Rx coil. But efficiency is only arround
5%.

http://www.youtube.com/channel/UCP6EEu4DG22gg-6l0L4ATJA

cheers Jens

Inducktion

Sat Aug 31 2013, 07:02PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Question, what would happen if you used a higher input voltage, but, say a different design? I'd imagine the allowable distance would increase but I don't know for sure. Like, PLL or something.

jechwa

Sun Sept 01 2013, 03:32PM

Registered Member #33559 Joined: Wed Aug 28 2013, 01:43PM
Location:
Posts: 5

Inducktion wrote ...

Question, what would happen if you used a higher input voltage, but, say a different design? I'd imagine the allowable distance would increase but I don't know for sure. Like, PLL or something.

No problem to increase the input voltage. But then the Mosfets becomes hot so I need a heatsink. The used irfp460 have high drain source resistance. Irfz44 are much better.

ARB

Sun Oct 13 2013, 01:38AM

Registered Member #27139 Joined: Wed Jul 03 2013, 06:16PM
Location:
Posts: 3

Thank you, Jens. In fact, I've tried the same thing as you did; by using intermediate resonators, I've increased the distance.
There is something that intrigues me: Why do you use at most 6 V? If you used 12 V, wouldn't it be better? I am using a 12 V battery with IRFZ44N MOSFETs. The only problem is, they tend at all times to short because no reason. Don't you have the same problem?

jechwa

Mon Oct 14 2013, 01:31PM

Registered Member #33559 Joined: Wed Aug 28 2013, 01:43PM
Location:
Posts: 5

ARB wrote ...

Thank you, Jens. In fact, I've tried the same thing as you did; by using intermediate resonators, I've increased the distance.
There is something that intrigues me: Why do you use at most 6 V? If you used 12 V, wouldn't it be better? I am using a 12 V battery with IRFZ44N MOSFETs. The only problem is, they tend at all times to short because no reason. Don't you have the same problem?

the transmitted power increases with the input voltage. 12 V are much better. but my mosfets are not mounted on heatsinks so they become too hot. the next setup will contain better mosfets and a heatsink. To avoid shortening the mosfets it is important to switch on the power supply abruptly and not softly.

ARB

Wed Mar 19 2014, 02:33AM

Registered Member #27139 Joined: Wed Jul 03 2013, 06:16PM
Location:
Posts: 3

Thanks to all of you for your replies.
I am still struggling for graduating from university using wireless power transmission as a topic in my bachelor' s thesis.
In order to achieve that, my teachers told me I must improve somehow Marko' s design, maybe replacing 1N4148 diodes with some digital control.
I would be very grateful if someone has any suggestions or ideas for this.
Regards.

Sulaiman

Wed Mar 19 2014, 06:10AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

One possible 'improvement' would be to drive the two main power switches/transistors with a known fixed frequency,
e.g. crystal oscillator with dividers,
final drive signal from the complimentary outputs of a flip-flop,
with buffers/drivers.
The transmitter resonant circuit can then be 'tuned' to the desired frequency by altering either inductance or capacitance.
Any receiver can then be tuned to the known frequency.

This should not affect efficiency in any way
BUT
it would allow any 'receiver' to use any 'transmitter'
whilst maintaining the efficiency of high-Q transmit & receive resonant sircuits
e.g. multiple transmitters along a route
or charging at any transmitter en-route,
i.e. an interoperable system, charging any receiver at any transmitter.

as a side benefit,
the operating frequency can be fixed
so that the fundamental and any harmonics are fixed
allowing easier bandwidth planning/usage.

P.S. an afterthought;
loading a transmitter with a receiver will probably (I haven't tried) 'pull' the operating frequency of the transmitter,
potentially reducing efficiency,
ESPECIALLY if more than one receiver is using a single transmitter.
Using fixed frequency drive avoids this problem.

P.P.S.
to demonstrate this you would have to build a few transmitters and receivers,
with similar but not identical frequencies/tuned resonators.
Then implement the fixed frequency drive system and measure the results.

Ben W

Fri Jan 30 2015, 03:36AM

Registered Member #54063 Joined: Tue Dec 23 2014, 01:05AM
Location:
Posts: 1

Hey, I'm interested in building this circuit, but have a couple of questions:

- What are the thicknesses of the tubing used in the transmitting and receiving coils?
- What are the number of windings around the toroid? What gauge wire?

Thanks, I'm in high school and I made a simple inductive coupling system which is able to achieve about 40% transfer at 1 inch, with a maximum separation being about 1.5-2 inches. I'm really interested in conducting more research of how the resonant frequency and multiple factors including passive tank circuits, changes in coil dimensions, and ferrite chokes.

I would greatly appreciate it if someone would be so kind as to rack together a bill of materials, to make it easier on myself.

Thanks for all of your help in advance.

P.S.- I couldn't find the circuit diagram for the secondary circuit being used in the system? Is it just a standard secondary circuit, and if so, what is the capacitor rating?

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