Contactless Electrical Current Transfer? 73
ferralis (Not an EE) asks: "Recently I've come up with a design for a very fun toy (to be unveiled later if I'm successful). What's missing is a means to send electrical power over a distance of five to ten centimeters (2-4 inches). I've done some research (mostly online) and have found extremely limited information. Even my beloved Google has forsaken me, and even my pleadings to eldritch information deities such as AltaVista have gone unrewarded. Can anyone help?"
"The way I see it, to do this a person needs merely set up a high-frequency electrical field using a larger coil (primary) and a similar but smaller coil (secondary) can be placed within it, creating an air-core transformer. Unfortunately I can't find the math or even anecdotes about what happens when the secondary is off-center, or there is more than one secondary introduced... and I am not looking to build a Tesla coil here. I can imagine that many toys could be built using such a system, and one would think the knowledge would be well known and readily available, but apparently it is not. For this application, efficiency is -not- an issue."
The coil thing should work. (Score:3, Informative)
Re:The coil thing should work. (Score:3, Insightful)
However he says he needs to do it over a distance of 2 to 4 inches, and there won't be enough coupling between the coils to achieve enough voltage to charge the battery.
I'm not saying that it is impossible, but rather exotic electronics means expensive electronics, and most toys are very price sensitive.
Anyway, that was Tesla's great dream, to transmit power.
Google failed? (Score:2)
As I regularly tell one of my friends : you have used too many pronouns / variables in that sentence in order to come to a conclusion / make any sense. That said, describe in tight detail what exactly you want to do and maybe we can help you figure out a way to do it.
I want to make something something and have it use some power to do something something and it will be cool if I can figure this part out. Surprisingly, given all tho
Re:Google failed? (Score:2)
Idiot. That assumes someone bothered to write a web page about air core transformer theory. It is dangerous to assume that all human knowledge is on the web, and that google has indexed it.
I did some transformer theory stuff when i was studying for my HND. Go buy to a library and borrow a book on Electrical Engineering. Its how people did research before the friggin net came along
Re:Google failed? (Score:2)
Re:The coil thing should work. (Score:2)
You'll need to get the magnetron out of a microwave (higher wattage is better, but danger increases with power) and build a wave guide horn for it, then simply point it at what you want to power, of course you might want to do something like build a faraday cage around the whole damn unit...
Enjoy, and please don't kill yoursel
Re:The coil thing should work. (Score:2)
You'll need to get the magnetron out of a microwave (higher wattage is better, but danger increases with power) and build a wave guide horn for it, then simply point it at what you want to power, of course you might want to do something like build a faraday cage around the whole damn unit...
You're insane. Microwave oven innards are extremely dangerous. Best case scenario is cataracts; worst case scenario is cooked liver or electrocution.
Besides, unless you got the impedance of the waveguide just right, y
Re:The coil thing should work. (Score:2)
However I digress, you can do this safely, it simply requires knowledge of microwave radation and exactly what you can and cannot do safely.
Now I'm gonna go press my head against the front of my microwave and watch some food cook for a while.
Coupling Electricity by Coils - Transformers (Score:2)
I have an electric toothbrush that charges wirelessly, I assume by using coils. Try dismantling one of those?
I'd imagine so. This technique is also used to recharge the batteries in some pacemakers. It's just a non-conventional transformer.
But the problem he has is the distance. The charger for the pacemaker, toothbrush, electric shaver, etc. can be brought very close to the device being recharged: he wishes to charge something at a distance. The holder will also be aligning the coils very closely.
Here'
This is more common than you think (Score:2)
ferralis asks about distance, but doesn't mention the size of the objects on either side. This is crucial if you are trying to use magnetic coupling, be
A question (Score:5, Funny)
I've thought of this before too (Score:3, Funny)
I mean, we've got wireless everything already, and all those radio waves and GHz signals are basically a form of energy streaming through the air, so why couldn't we do it with electricity?
Think of the bliss a wireless power bar would bring.
Patent pending.
Re:I've thought of this before too (Score:3, Informative)
Re:I've thought of this before too (Score:2)
Re:I've thought of this before too (Score:3, Informative)
The reason wireless electricity is a problem is that as distance increases linearly, power drops off exponentially
Actually, cubically.
Re:I've thought of this before too (Score:2)
Re:I've thought of this before too (Score:2)
Or quadratically, if the distribution is from a line instead of a point....
Touché. :-)
Re:I've thought of this before too (Score:2)
Re:I've thought of this before too (Score:4, Informative)
No that's not the reason, just pick a medium that can be focused. I'm sure you can transmit power wirelessly using microwave or laser very long distances. (Consider that nearly all of the energy we use on Earth has been "transmitted wirelessly" from the Sun).
The problem is safety - if anything or anyone happens to be in the path of such a transmission, they get fried.
Here's a link about using microwave to transmit power from the moon [spacefuture.com].
Re:I've thought of this before too (Score:1)
Re:I've thought of this before too (Score:1)
You meant that to sound stupid, as a joke, right? Focusing puts the power that decreases exponentially (or quadratically, as menscher so helpfully pointed out in his half-correct post - inverse square law anybody?... not inverse cube.) into a smaller area... no point in dissipating your power in directions where it's not needed. However, it's not a laser... and even they dissipate exponentially, as their spatial coherence is not perfect.
Re:I've thought of this before too (Score:2)
Well, I'm no scientist really - but does the power really decrease? Where does that energy go then?
Re:I've thought of this before too (Score:1)
Computers are too easy to use (Score:3, Informative)
A great many turbines will break apart if they lose their loads and overspeed, standard reaction-type steam turbines and many water turbines among them. The virtue of the Tesla turbine is that its pieces are very simple, its vice is that it is woefully inefficient com
Re:I've thought of this before too (Score:1, Funny)
Eternal bliss, as you step between it and your home network and wind up arcing 110 volts.
Well maybe not eternal bliss, if you have the evil bit set.
Prior Art (Score:2)
Found this on Google (Score:4, Informative)
or this? (Score:3, Informative)
Induction (Score:2)
Re:Induction (Score:2)
Re:Induction (Score:3, Informative)
Another way would be an infrared laser and a solar cell, but I don't think you can get much power out of it.
easy (Score:5, Funny)
Re:easy (Score:1)
One solution... (Score:5, Funny)
Re:One solution... (Score:3, Funny)
Re:One solution... (Score:3, Informative)
Considering that the "ZipZap" RC mincars use something like this, I would guess that it's a viable solution. I'm amazed that the clone I bought had the car, motor, steering, rechargeable battery, radio control transmitter and in-car receiver, etc, and with manufacturing and trans-Pacific shipping it got ito my hands for $6. Chinese labor is cheap!
Re:One solution... (Score:1)
Apology accepted
IIRC the tiny RC cars use a large capacitance capacitor to store their energy, which is why they can be charged quickly by the controllers.
Re:One solution... (Score:3, Interesting)
(I'm proud of that run on up above, yes I am).
--
Evan
Re:One solution... (Score:1)
Re:One solution... (Score:2)
Re:One solution... (Score:1)
So does dumping your toxic waste untreated into the environment.
Carrier Mice (Score:1)
What the hell are you people learning in schools these days? Are your teachers clowns?
Well... (Score:4, Funny)
Obligatory (Score:2)
Huh? flashlight + solar cell = wireless power (Score:2)
Details? (Score:4, Insightful)
Unfortunately this is one of those questions like you get on sci.electronics.* which doesn't include the basics like how much power is required; at what voltage and current levels, AC or DC, what frequency, can "it" run unconnected (e.g. on battery) and if so for how long (application-wise, not technology-wise), etc. etc.
Barring nice engineer-friendly technical specs, at least outline more specifically what you're trying to do, at least in vague terms, would be more helpful. Starting out by saying it's a product idea (rather than just some hobby thing) was probably mistake if you're paranoid about competitors.
Without some minimal specifications of this sort, absolutely any answer you get will either be hopelessly vague, utterly useless or simply a troll.
Re:Details? (Score:3, Informative)
Details:
Type: DC (at the end, I'm assuming high-freq AC in transit)
Voltage: Between 3 and 10 volts, the curcuite is pretty flexible.
Current: In the milliamp category, basically just charging one tiny NiMH battery in a waterproof enclosure that I'd prefer for ease of use/durability to have no insertion points.
Thanks!
rectenna (Score:3, Interesting)
google [google.com]
Re:rectenna (Score:1)
frying depends on the frequency and power (Score:2)
Re:rectenna (Score:2)
Power is the key, sure, 1000W microwave oven magnetron will damn certainly fry (well, boil) everything, but try hopping in front of 1000W laser for example and come back to tell that visible light doesn't fry you equally well.
Go to WPT (Score:4, Informative)
Wacom Tablets (Score:1)
You didn't state how much power you need. (Score:4, Interesting)
Since you didn't give us any information on how much power you actually need (a few milliwatts I hope...) then all I can tell you is to avoid air coils. You'll get almost no practical energy transfer. Make the smaller coil fit inside the larger coil, and put a suitable core inside the smaller coil.
Alternately, if you want two flat faces facing each other, get two large cheap speakers. Remove the cone and coils from the magnet assembly. You may need to remove the magnets themselves and replace them with another ferromagnetic material. Place new coils where the old speaker coils were (wrapped around the core inside the assembly). Face them to each other and put low voltage AC on one side.
There are transformer books which will give you the information you need to accomplish this. It's hard to give you better information than that, though, without knowing the power requirements of your device.
If this [microbeam.ch] PDF treatment on the subject doesn't help, then you probably don't have enough knowledge to correctly design one and you ought to simply start toying around with different designs until you find a suitable match. If/when you mass manufacture the device you'll want to pass it by a real engineer who can redesign it for you. Pay attention to the references in the paper for more information.
-Adam
FCC Class B certification (Score:2)
Oh, I'm wrong! Laser! (Score:2)
Re:FCC Class B certification (Score:3, Funny)
The catcher runs a generator. Now all you need is
an infinite supply of metal balls.
Okay, no metals balls? Use one of atmospheric gas
molecules, alpha particles, or photons.
(1) Atmospheric gases: Use a motor on the power
source to drive a fan. Use a fan on the power sink
to drive a generator.
(2) Alpha particles: Nevermind. This is a non-starter unless you can do thermionic power.
(3) Photons laser on the pow
I don't mean to troll, but (Score:1)
Or if you are too lazy, pay some college physics student a couple bucks and they'll get you the info you need in no time.
I hate to make the same point that many have made before, but aren't there any better ask
Sparks (Score:1)
True wireless electrical current transfer occurs as a spark (think lightning). That is current flowing through whatever meduim between highly positively charged and negati
Small beef... (Score:2)
I know that this is a case of pedantic nit-picking coming from an physics ignoramus, but maybe it points ot a way to get this guy's job done. If you get the right frequen
Batteries (Score:1)
Electromagnetism (Score:1)
Short-range power transmission (Score:4, Informative)
Anyway.
Short-range inductive power transmission works reasonably well. It's commonly used to recharge electric shavers and toothbrushes. Considerable power can be transferred this way. The GM EV1 electric car used an inductive charger, where a flat "paddle" containing a coil was inserted into a rectangular slot in the car.
Efficiency improves with frequency. The EV1 charger ran at 400KHz or so. But you have to take precautions not to become an RF emitter, and get FCC type approval. If you stay with 60Hz, that's usually not a problem.
Coil area helps. If you can use large diameter coils, bigger than the air gap between them, it will probably work.
If you don't need much power but want directionality, one interesting option might be to have a bright light aimed at a solar cell. You'll be lucky to get 1% efficiency. If that's enough, you're done. It's safe.
If you need very little power but have room for a physically large antenna, you might be able to build something that runs off ambient RF fields. Just make a big flat coil, wire it to a diode, and see what comes out. The output will vary enormously depending on how close you are to a transmitter. If you're lucky, you might be able to power a clock.
Do you mind if things get wet? (Score:3, Funny)
few suggestions (Score:1)
- try searching for "contactless smartcards" .. i don't know much details about how is done, but these devices use contactless transmited power ... also see ISO14443 & ISO15693
- check Mifare & NFC technologies from Philips and Felica from Sony
- as a side note, my electric toothbrush(philips jordan) has a docking/charging station wich does its job without any metalic contact - it's just a plastic-on-plastic touch there, i remember being a bit boggled by the device when i first saw it :).
Again
Biot-Savart (Score:2)