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Wireless power- my own setup and questions

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rp181

Wed Apr 29 2009, 10:18PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Hey all,
I just got a function generator, and it delivered today. (

)The square wave gets horrible at higher frequencies, it looks like a sine wave, with an asymmetrical top). I rigged up a simple setup, to just test the basic theory. I wrapped a coil (4-5 turns, around 1.75" ID, unknown gauge), and tested the resonance with a 5.6nf ceramic capacitor in parallel. The resonance turned out to be around 1.3mhz. The other coil I made was around 1.27 Mhz, I figured close enough. The coil did pick up the receiving power, I just had a scope connected to the output. Now my questions:
1) The receiving coil is 180 degrees out of phase. Is this just due to the resonant cycle?
2) When The coil was connected, the resonant frequency jumped to about 2.1 Mhz. I do not know if this was me, is there something that could have caused this?
3) When I move on to switching higher powers (I plan to go up to 1kW with luck), how do I switch this power? Are regular MOSFET's and IGBT's capable of handling this? I want to try up to 5Mhz.
4) How does the frequency affect the the performance?
5) Am I measuring resonant frequency right? I just connect the function generator and scope to the LC circuit, and play with the function generator until the sine wave peak is highest.

If anyone has any good articles about this, please post

Thanks in advance.

twist2b

Wed Apr 29 2009, 11:17PM

Registered Member #2086 Joined: Tue Apr 21 2009, 02:33AM
Location:
Posts: 117

First off, what you are explaining (waves) sounds like a

SawTooth wave... you obviously just have the wrong setting?
The link you posted does not work.
The ones I can answer (I don't know how right I am -_- but I studied this alot, and starting it in the summer)
5Mhz is NOT enough, you need 10, and even then your going to get only so good results. POWER MOSFET. :P

frequency = critical, the whole point of MIT's research was to find a method to keep the power outside of the danger zone (we have been able to transfer for a WHILE, but its never been ideal)
The frequency effects the efficiency of coupling.
The faster the coupling rate, the less loss (which in a small scale, it is more important)
Range and rate coupling, I don't expect you to understand ALL of it, but just get the idea of how much its going to effect the formula:

(da1/dt) = -i(w1-iT1)a1+ika2 , (da2/dt) = -i(w2-iT2)a2+ika1

The amplitude (a1(t) and a2(t) )
eigenfrequencies are the w1,2
T1,2 are the resonance widths due to absorption, radiation, etc.
K is the coupling coefficient.

if the resonance is EXACT (w1=w2 and T1=T2)
You should be a pretty happy man. And the coupling should be better.

Obviously this formula is more theory then actually realistic, but its supposed to give you an idea of what your going to end up with.

antenna length is wavelength/2 and this is applicable to a length of wire.

I am prob not the best to answer these questions (sorry -_- )
But i tried, hope I helped at least some.

BUUUUT, seriously, ..life gives you lem.. resonance, make resonade..

rp181

Wed Apr 29 2009, 11:40PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Interesting. I have seen people trying to get high frequency, and others trying for low (I know marko is trying for low). I will try both, and see what happens.
I do not know why the link does not work, but it is a BKprecision 4007DDS, so the limit is 7Mhz.
The wave setting is on sine, on higher frequencies, the square wave looks more like the smooth-wave on you chart.]

The coil seems to work semi decent right now. Powered by only the function generator, and a receiving coil 3" away, a 3v white LED lights brightly.

Bjørn

Wed Apr 29 2009, 11:53PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Your URL started with (http instead of http, it should work now.

How are you measuring your square wave, for example a 20 MHz oscilloscope would not be able to show a very good 7 MHz square wave.

twist2b

Thu Apr 30 2009, 12:34AM

Registered Member #2086 Joined: Tue Apr 21 2009, 02:33AM
Location:
Posts: 117

rp181 wrote ...

Interesting. I have seen people trying to get high frequency, and others trying for low (I know marko is trying for low). I will try both, and see what happens.
I do not know why the link does not work, but it is a BKprecision 4007DDS, so the limit is 7Mhz.
The wave setting is on sine, on higher frequencies, the square wave looks more like the smooth-wave on you chart.]

The coil seems to work semi decent right now. Powered by only the function generator, and a receiving coil 3" away, a 3v white LED lights brightly.

Wow, congrats man!!! I did not know low frequencies had any success.
post some pictures if you don't mind.
Also, can you post a schematic?
Did you add a dialectric?
Tell us what happens when you put your hand in front
Now, try a 5V with a greater distance. Shoot for medium range (as you try to progress) and see what happens.
Keep us updated, this is one of my favorite subjects.

rp181

Thu Apr 30 2009, 02:26AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Updates:
I Added a IGBT, and connected my bench PSU, rather then just the function generator. The IGBT makes the input waveform a bit funky, but the output is still sine. I upped the voltage to 32v, and the LED with light brightly from 1.5 feet away. This is with new coils, 5-6 turns of solid 12 AWG, around 2.5" ID. I will take pictures now.

Something interested I noticed. Usually, when you are on the resonant frequency, and move away, the power drops to 0. For some reason, my coil seems to have two resoant points. At around 100khZ, it lights brightly, drawing around 500ma. When I up it, it turns off, and starts again at around 930khz, but this time, with only 40ma, with the same output.

Can these do anything to equipment? My function generator froze a couple times, but still gave a output, i just couldn't change it until i restarted it. My PSU displays error 006, which is a header error. This should only come with serial communication with a computer, but it is being triggered from some reason. I just recently put a diode on the output, it seems to prevent that from happening, but I have not ran it long yet.

I will go take pictures now and try putting my hand in between. All I have tried is ferrite, which compleatly shuts it down only when the reciever coil is perpendicular to the transmitter. Otherwise, it has no affect.

@bjorn
Yes, I am using a 20mhz scope. I guess that is the problem.
EDIT:
So the diode didn't work, I got the error again. You can see it in the video. The video came out dark, but you can still see all the main things.
The video is still uploading, but i probably won't come on again today. You can look under "zanta24" channel on youtube.

EDIT EDIT:
here it is:

twist2b

Thu Apr 30 2009, 06:47PM

Registered Member #2086 Joined: Tue Apr 21 2009, 02:33AM
Location:
Posts: 117

Nice. Personally I still stick to my point, if you want medium range, you need higher herts (10 :P )
I did not know you just wanted wireless with range not the current issue.
They say that the range is dependent on the wavelength, and you want to reach it at a half wave (something like that)
I wish you showed us what happened when you put your hand in the way. Did you add coupling? I could not see.

Congrats though, very fun right?

BTW - whats with the thumping>?!~

rp181

Thu Apr 30 2009, 08:37PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

The thumping is just from my camera's bad sound pick-up. I used a 5.6nf capacitor in parallel, currently the smallest capacitor I have. I tried without a capacitor, but performance was dismal.

When I put my hand in the way, or some paper, nothing happens. When I put my calculator in the way, the output drops very little.

...

Thu Apr 30 2009, 09:57PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The issue with the square wave is probably an artifact of your oscilliscope, you could try running it through some cmos logic (any old not gate or the like would work fine) and look at the output that that, it will have a square wave output.

As to damaging your equipment, yes it is entirely possible to damage your equipment, and when it starts to act funky it is time to shut everything down and do some reseach on how to protect it. There is no point in blowing out a $500 power supply when all you needed was a $.25 filter on the output to keep the rf from getting back into it.

I would recommend moving your work coil a little further away form the equipment (if you can light a led with the coupled power from 2ft away, imagine what it is doing to the precision electronics in your psu!), add a gate driver between your signal generator and the power transistor (for small semiconductors the ucc37322 would work fine, for anything in bigger than a to-220 package go for a one of IXYS monster gate drivers), adding a low esr 100ufd electrolytic, 10ufd tantalum, and 100nf ceramic capacitor across the output of your power supply, and if your circuit won't mind it a small inductor after the capacitors to keep transients from making their way back in.

Also, an IGBT is a very poor choice for super high freqiency stuff (they usually start to run into trouble in the 100s of khz, even 1mhz would be pretty good for one), and switch over to mosfets. You are basically building a 1mhz am transmitter, and you start need thinking as such.

rp181

Fri May 01 2009, 12:46AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Thanks for the reply.
When I switch between wave modes, the sine works better anyway. I stopped doing anything with it for now. For the filter, does it matter the type? I do not have any tantalum in that range, but I have some lyctics in that range, if not, I will buy some. I am currently using a TO-247 IGBT, ultrafast from ST. I will add a gate driver on there, and see if there is improvement.

Some more questions:
How do I measure output power reliably? I can measure the voltage with a capacitor on the output, but how do i measure current? I tried a rogowski coil, but The waveform looked the same as when there was nothing through the coil, and it was on. A direct multimeter approach also won't work.
Do you have a MOSFET suggestion? I will look through sites later, but I always doubt my self

I plan on eventually moving up to 1kW.
Does anyone know where I can get solderable breadboards? The ones that are in boards, like the STAMP and other micro controller boards.

I will do some more research on RF AM transmitters. Are there any laws I need to worry about?

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