I need your help. IPT (Inductive Power Transfer)

THIS INSTRUCTABLE IS NOT YET COMPLETE. I have been trying to build a wireless charger but have come across a problem. I have documented what I have done and learnt so far. Hopefully from this you can see my errors and help me out. Please read the last page to see what I think the problem is and suggest any ways to get around this. THANKS

The Project
I am trying to build a circuit that will allow gadgets that are usually charged by USB to be charged wirelessly. As an example I am reverse engineering an A4tech battery-less mouse. However it is too great a challenge for me and I am seeking help from you. I thought it would be better for me to turn this into a group effort than to ditch the project. I will give a detailed description of what I have built and learnt and hopefully you can tell me where I went wrong.

Step 1: Background Information

Transferring power wirelessly is reasonably simple. If you think about it, all transformers are wireless. But we want something that's truly wireless. Like the Splashpad (see picture). It is pretty much a transformer with an air core.
The mouse I was talking about (see other picture) in the introduction is exactly the same as the Splashpad it uses induction to transfer power across an air gap. This is the same technology as RFID; in fact it uses this to communicate with the pad. To make our own wireless device we need to know more about induction.

Comments

[aaronmurray]

Great post, thanks for all the accompanying info. Is it possible to dim the secondary by way of reducing the voltage through the primary or does that mess up the tuning of teh coils?

[akshaya ladwa]

i need to charge my mobile by wireless system using wifi radiations & signals

[davelanda]

very well...

[MadScientist101]

how many microfarads is 181K ?

[spark light]

180 pF
or
.00018 uF
here's a handy link:
http://www.electronics2000.co.uk/calc/capacitor-code-calculator.php

[awmayhall]

So I tried using your circuits in a circuit simulator. I couldn't get them to work properly.

[ARJOON]

i need to connect one of the circuits to a transformer without a centre tap how can i do it

[Aiden1015]

 I think your problem is you're having 2 different resonating frequencies. the primary may be at one, but the secondary is at another, thus a low, almost 0 voltage. the easiest thing would be to play with inductor lengths. or figure out which capacitors on the mouse, with the inductor, create the resonator, figure out the capacitor value and calculate the needed inductance for your secondary.

[cerincok]

From your video, the circuit seems to be working greatly. But less power are transferred. What voltage did you get at your secondary coil?.

[puffin_juice]

I dont think my meter can measure such low voltages at such high frequencies. I got a reading of 0.015mV while the LED was glowing.

[BinnX]

Can you tell me which transistors you used.... its no. and what is your wire gauge for primary secondary coil.

[cerincok]

Yep...i think you're right. Maybe you should use an oscilloscope to measure the exact voltage value..

[faham]

Your problem is simple: you have an impedance mismatch. This means that your primary coil is not well matche to the signal source, and to make it work you will need to match the signal source impedance to the coil impedance. Also you can consider the coil and the parallel cap as an LC resnance circuit acting as once circuit. You need a transistor driver and voltage multiplier, do not worry too much about the current now but please lift up the voltage as of now so you can get more transfer of power. Also remeber that the USB is limited in power and the manufacturer have made accurate calculations on how much power to transfer vs matching the impedance. What I would do is the following: The antenna coil must be driven by higher voltage higher current signal source first, since the USB cant provide higher current lets focus on higher voltage. Now charge up this high voltage in a cap and drive it to the coil via a MOSFET transistor with low ON rDS resistance and proper gate charge. I bet once you do that you should be able to then measure much higher voltage than what you reported. The secret to solving your problem is impedance matching... Please let me know how it goes and call me if you have a problem. Good luck... By the way I worked with high voltage security circuits and TV and power transfer circuits and I can help you as my time allows me. 

[EvilMika]

I'm currently working on a similar project.  Have you looked into using a FET Driver instead of a 555 timer?  This will lead you to much higher voltages and current, thus a stronger magnetic field. 

Also, how did you wind such nice coils?

[killersquirel11]

4 Nails and a wooden board
4 pegs and a pegboard
4 pencils and two friends
A very well-trained cat

...basically anything that has the ability to have four rectangularly spaced supports ought to do the trick

[acmefixer]

"A very well-trained cat" -- Hahahahahah!  Cats don't have masters, they have staff!!  ;-)

[framistan]

It is possible your circuit is using more milliamps than your charging circuit is delivering...  Ohms law works only when your source of AMPERAGE is UNLIMITED...  In the real world, you are limited by what your SOURCE can deliver.  For example, if you place two tiny 9volt batteries in series, you will have 18 volts... connect this to your automobile in place of your car battery.  Ohms law says it should work... but you know there are not enough AMPERES AVAILABLE to do that job.  The same is true on little circuits that only draw milliamperes.  If the current source is too low, then amperes will not be delivered and THEN you see the voltage sag down low as result.

[acmefixer]

In the Real World, you're telling us what you observe on the outside of the battery.  But inside the battery there is actually an _internal resistance_.  If that were very, very low, then the 9V battery would deliver as much current as a car battery, but it's not low.  So when you attempt to run your car with it, the voltage drops across the internal resistance, and all you get outside the battery is a very low voltage, what's left after the V drop across the internal resistance.
BTW, if you try to run the car with the two 9V batteries, they will get hot because of the power dissipated in the internal resistance.

There are these car starting packs that you can buy that are very small, and put out a very high current because their internal resistance is very low.  Thus they are able to turn over the engine and start the automobile.

[Gjdj3]

I don't know if you still check this instructable, or if you're even an active member of the community, but I think I may have found the problem.

You say throughout the instructable that you want a high frequency. For an inductive coupling application, however, high frequency is not a good thing. To fix this you could try adding a capacitor in series with the coupled signals, as sort of a filter. You could also try lowering the frequency.

[arhodes18]

 Can anybody explain the part of the schematic he added in step 10 I can't for the life of me understand it!!
PLEASE!

[hms1018]

Check out this person's instructable!     http://www.instructables.com/id/Wireless-Power-Transmission-Over-Short-Distances-U/     It's pretty cool!

[DarStarr]

Dont power it off the pc. Grab a more powerful adapter that plugs straight into the wall.

[Masteroffencing]

i agree with darstar u should just get a wall mount for it

[gamerjunky09]

Yeah I also agree. I might try to start my own project for my black berry. I will post my figures as soon as i start.

[acmefixer]

A few observations. The smaller coil looks like it doesn't have enough turns. More turns should help. When I say more, I mean double or even more. The full wave bridge is a power waster. I would remove two of the diodes and double the number of turns in the smaller coil, turning it into a center tapped coil. This and the two diodes make a full wave rectifier. The diodes should be low loss, use 1N5817 schottky diodes for these.

[killersquirel11]

Also, with what little I know of electronics...
Would increasing the voltage and number of coils on the primary also provide a marked improvement?

[breadpig]

Hi

Anyone has infomation on how to determine the mutual inductance or coupling factor? And also the equation to determine the inductance of the coils?

hope if anyone can help me :(
rgds
alex

[EvilMika]

Breadpig, this is simple an air-core transformer so M should follow as such:
M=N1*N2*Phi=K * (L1*L2)^.5
where N1 is the # of turns on the primary, N2 is the # of turns on the secondary, and Phi is the permeance of air.

From this you can extract K, the coupling factor,
K= (N1*N2*Phi) / (L1*L2)^.5

As for determining the inductance of the coils, if you do not have a multimeter or some other device to measure this, you can sweep the frequency on a frequency generator looking at the voltage across a parallel cap and your coil.  The peak voltage is then related to 2*pi*f = 1/(L*C)^.5

[paulm]

 Make sure you are perfectly aligned with the primary coil, at an angle of 90 degrees, you will get no power.

also, where is the power regulation for the mouse?

[freeh18]

 why are you using square wave?
why not sine wave ?

[Xellers]

http://www.youtube.com/watch?v=SSgo_N-5JOg

[robotkid249]

PLEASE READ:

What is you simply had an wall wart that supplied 9VAC after it conevrted the '120 VAC. Then run a transistor so the 555 timer, turns the Wall Wart on and off at 120 kHz, providing you with the 120 kHz square wave, AC signal at 9VAC

[edfel01]

wow u put alot of work into this good job even if its not done yet

[headcipher]

Have you tried using a much lower frequency? I know it may not be exactly the same thing, but I am a utility locator, and I use inductive antennas daily to apply a alternating current to a pipe or wire. I do not pretend to understand the physics, but I can tell you the results I see. When using induction I have various transmitters that project signals at these frequencies: 9.82khz, 33khz, 65.5khz, 83khz, and 200khz. My most advanced couple of recievers also measure the milliamps applied to the target for identification purposes I. E. the signal with the highest rating is the target. The lower the frequency the higher the amp reading, but on the otherside of the coin the lower frequency has less penetration. If you ever have an opportunity to use one of these pieces of equipment, turn it on on a plate of any kind of metal and the lower the frequency you use the more likely you will hear the metal vibrate.

[TheMaskedAvenger]

I recently read about an MIT experiment that took this kind of thing to the "next level." It involved using something called "evanescent waves." Here's the article: http://technology.newscientist.com/article/dn12014-wireless-power-could-have-cellphone-users-beaming.html
Does anyone here know more about this? It seems to me that a magnetic field, unless it was really, really strong, would not be able to do this kind of thing.

[tanmanknex]

well, TECHNICALLY it's not really a magnetic field. it's really an electromagnetic field, AKA radio/gamma/microwaves/light.

[Meigus]

I think the problem here is that you simply don't have enough magnetic field strength. The whole point of this newer style transmission of energy is specifically that it's not transferred through light-based resonance. Even if you multiplied the antenna alot, it'd be like someone with a radio near an x-watt transmitter - the inductance of the wire is too small to pick up enough signal to blow. A design advice: try copying speakers. The whole point of speakers is to drive sound, however, speakers work by a permanent magnet being pushed back and forth, in your case it would create a pulsed magnetic field with no modification, other than the possible removal of the springy styrofoam cone (unfortunately, that foam also holds it in place, so you should probably leave it in as it doesn't impede magnetism). This would be a perfect starting point as a second speaker (say, part of a two speaker set) at most, like, 1 inch distance away and proper orientation (facing head on or completely away - any other would incur loss) would feel a significant change in magnetic field, and induce current in it's own winding. A more extreme scientific use: Using the all-purpose magnetic field "resonance" that occurs for any ferromagnetic material, there've been experiments where a magnet was put in someones fingertip. With short training, they could detect positive fields, negative fields, and even low-hertz fields by the magnet pushing/pushing/vibrating. I think the whole point of what I'm trying to explain is this: Instead of a pure electromagnetic wave, which I think you're trying, I believe you MUST transform a constant field into a waved constant field, whether it be normal-magnet based or a DC electromagnetic. This would make a resonant magnetic wave, but not nearly as high frequency as what we'd consider light. A too high frequency actually would be counter productive, there should be a push or pull, too fast and the reciever doesn't have enough time-strength to act, this exact same principle applies to a specific efficiency of a DC motor (I remember the term now, it's called "slip" look it up on wikipedia). An electromagnetic field would only be useful for the transmitter (to strengthen the range and locking strength). I'm pretty sure the constant field is necessary, so for a test, try using a speaker laying face down on your inductor plate (the one you want your mouse on). A speaker should have significantly more windings than your mouse or pad, so a volt-meter should read a high voltage being induced in the speaker. Just try to keep the frequency under 20,000 for the speaker to resonate properly (it should even make an audible tone if the wires from the speaker are shorted). Try a speaker-test after you make adjustments to the pad to improve the efficiency of the transmitter, should make it faster, easier, and more consistent than modifying the mouse. And if you claim "well a low frequency would have to low resistance" then you either need more windings, or a better inductor, or some such thing to increase inductance. The resistance should be basically infinite when the opposing inductor isn't allowed to short/do work. The inabilty to have an infinite resistance is why wall transformers are ALWAYS drawing power, even when the opposite windings aren't connected to anything. And again, if your inductor is in the field but "switched off", 0 ohm transmitter resistance change is failure to transmit power, infinite resistance is perfect transmission.

[tanmanknex]

um... you have pushing twice in the third paragraph on the last line. did you mean to do that?

[thermoelectric]

After looking at the picture of the primary inductor (the close up shot) it seems to have only a couple of turns, Is that true or are my eyes decieveing me? If it's only a couple of turns, it is probably set up sort of like a tesla coil in some ways. That might help you... Just have a look at tesla coils and see if there are many similarities, I think there are..

[viking_r]

HI, I am working on the same project.(for my final year). right now i am working on the primary coil and acc. to my calc. i need to transfer .24 henry though it. for that purpose i need a 32awg wire(copper). my question is do i have to use copper windg. or can i use aluminium wndg also??? i think puffin_juice is usin al wire in video. for rest of the circuit i am currently using function generator.... one more thing is it possible for you guys to post the full circuit diag.(or the one used in the video by puffin_juce) thanx