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Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
I am trying to wirelessly charge my cell phone since plugging it in is just too much effort. My first experiment went very well. I set a NE555 to 155KHz 64% Duty cycle connected to a largish coil and was able to power an LED. My next logical step is to increase the power by adding a 2N3055 to the output of the timer. But, whats the next step? Someone suggested that I add some Caps to the coils to make them resonant? Any suggestions?
Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Hey man. I've been looking at the same thing for weeks. If you have not already checked Marko's thread, go here , there is a lot of discussion on it.
I was able to successfully replicate his build, but have not yet tried building a receiver coil for any of my old phones. What stopping me is the temp of the receiver cap.
My build has a 80nF cap bank on the transmitter, and a matched 250V 80nf WIMA poly cap on the receiver. My receiver cap gets to about 110 C after 90 seconds of operation, so I shut it down. Rectified output on the receiver is 5V to 12V depending on distance to the transmitter.
You can get the right voltages to charge the phone, but may melt other components. The smaller the receiver cap, the faster it heats. The smallest one I tried was 63V 80nF, and blew up in about 1 second. My larger caps run longer, but won't fit inside the phone's plastic shell.
This is not to say it can't be done. Fulton Innovation has a complete line of products for wireless energy transfer, powering everything from cell phone chargers to blenders and stove elements... The Youtube vids from CES 2009 demos can be found here -
Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
Wow. Im not too concerned with keeping it inside the phone case. My goal is to be able to fit the reciever, phone and car keys all in one pocket. =) . 110C wouldnt feel to good in my pocket though...
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
Note that all the demonstrations underline one very serious limitation -- range. With a highly optimized setup, one could realistically expect ranges in the neighborhood of a handful of feet, at efficiencies ranging from 50% to less than 1%. It's definitely not something you'll be able to walk around with in your pocket, unless your pockets are extremely large, or you don't walk far.
Some clever experimentation could allow you to set up a charging zone of some sort, though, to top off the phone when you're in a commonly-visited area. A night stand or work desk, for example. Sadly, even a very good set up will result in a fair amount of wasted energy as compared to simply plugging the phone in, which is frowned upon these days. Still, it is fun to tinker with; Marko's thread has a wealth of information to get you started.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
One thing I'd be interested in seeing how it works is using relatively low intensity RF (either by low power at close range, or moderate power at range) to slowly charge up a capacitor and give a burst of charging. This would be suitable for overnight charging as most cellphone chargers push power into those lithium batteries at 0.5-1C and charge from almost dead to full in 1-2 hours. Could an overnight charge, or low-intensity energy capture for topping up charge be practical? Perhaps a small 'mousepad' sized RF coil where objects such as cellphones, PDAs, etc can be charged.
Although I don't use my cellphone much, so maybe that is why charging is so fast. PDAs and smartphones probably draw even more power...
Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Chris Russell wrote ...
Note that all the demonstrations underline one very serious limitation -- range. With a highly optimized setup, one could realistically expect ranges in the neighborhood of a handful of feet, at efficiencies ranging from 50% to less than 1%.
Bang on. Not that I could get more than 8" to work. I wasn't looking to either though.
Chris Russell wrote ...
It's definitely not something you'll be able to walk around with in your pocket, unless your pockets are extremely large, or you don't walk far.
I don't agree here. My receiver (no PCB) was small enough to fit in my jeans pocket. I could easily build a small box to fit it in, and strap it to the back of an old Blackberry, only increasing thickness by 50%. That may be big for pants pockets, but in an average jacket, no problem. My goal was to fit it inside the original phone's case.
aonomus wrote ...
One thing I'd be interested in seeing how it works is using relatively low intensity RF (either by low power at close range, or moderate power at range) to slowly charge up a capacitor and give a burst of charging. This would be suitable for overnight charging as most cellphone chargers push power into those lithium batteries at 0.5-1C and charge from almost dead to full in 1-2 hours. Could an overnight charge, or low-intensity energy capture for topping up charge be practical? Perhaps a small 'mousepad' sized RF coil where objects such as cellphones, PDAs, etc can be charged.
Although I don't use my cellphone much, so maybe that is why charging is so fast. PDAs and smartphones probably draw even more power...
The low power/tighter coupling works in Marko's setup. I ran my transmitter off a 120V-12V transformer connected to my variac. At full power (12V) you can still control the voltage output of the receiver by moving it further away. From 1/2" to 6", I can get a rectified 12V DC on the receiver. From 6" to 8" it drops to ~4V DC.
A true Cellphone (eg. Motorola Razr) will charge on just about any charger out there. Smartphones, in my experience, are a little more picky. And the wireless charging mousepad? That was one of eCoupled's first developments.
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
Zenador wrote ...
I don't agree here. My receiver (no PCB) was small enough to fit in my jeans pocket. I could easily build a small box to fit it in, and strap it to the back of an old Blackberry, only increasing thickness by 50%. That may be big for pants pockets, but in an average jacket, no problem. My goal was to fit it inside the original phone's case.
I should clarify; it's not something that you'll be able to walk around with in your pocket while charging. The aforementioned problem of range prevents that, especially for a small, pocket-sized coil. You could certainly build something with a very short range that would fit in one's pocket, perhaps even something that would adhere to the back of the phone, or slip on to a keychain. I just wanted to point out that unless one willing to wear a backpack coil, or do something clever like stitching a large coil into a sweater, one should expect to have to set the receiver down very near the sending coil.
aonomus wrote ... Perhaps a small 'mousepad' sized RF coil where objects such as cellphones, PDAs, etc can be charged.
The idea of having a charging mat has been tossed around before, and even demonstrated, IIRC. It's an inherently attractive idea to me, especially since it would be trivial to have the mat sense whether a load is present, and shut off when no devices are present to consume power, thus preventing RF pollution in my immediate area. I'm not sure why it never got off the ground, commercially speaking. I'd guess that the lower efficiency is a turn-off for potential investors and marketers. My own phone admonishes me to unplug the charger from the wall when it's charged; presumably the manufacturer is worried about the .01W the switchmode charger will draw when not in use. I'd also wager that the potential loss of aftermarket charger sales prevents much interest from phone manufacturers.
Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Chris Russell wrote ...
The idea of having a charging mat has been tossed around before, and even demonstrated, IIRC. It's an inherently attractive idea to me, especially since it would be trivial to have the mat sense whether a load is present, and shut off when no devices are present to consume power, thus preventing RF pollution in my immediate area. I'm not sure why it never got off the ground, commercially speaking. I'd guess that the lower efficiency is a turn-off for potential investors and marketers. My own phone admonishes me to unplug the charger from the wall when it's charged; presumably the manufacturer is worried about the .01W the switchmode charger will draw when not in use. I'd also wager that the potential loss of aftermarket charger sales prevents much interest from phone manufacturers.
Not only has it been demonstrated, it's commercially available, for at least one mobile phone. The Palm Pre has an accessory charging "station." The Touchstone station retails fro $79 CAD from Bell Canada
I think it's only a matter of time before this becomes main stream.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Chris Russell wrote ...
Note that all the demonstrations underline one very serious limitation -- range. With a highly optimized setup, one could realistically expect ranges in the neighborhood of a handful of feet, at efficiencies ranging from 50% to less than 1%. It's definitely not something you'll be able to walk around with in your pocket, unless your pockets are extremely large, or you don't walk far.
I agree that range is an issue; but there's no particular theoretical limit. I think under optimum conditions range is typically limited to about one or a few transmitter coil diameters or quarter wavelength (whichever is smaller).
In principle you could have a coil the size of a wall, or the floor. (With big *thick* litz wire!)
wrote ... Some clever experimentation could allow you to set up a charging zone of some sort, though, to top off the phone when you're in a commonly-visited area. A night stand or work desk, for example. Sadly, even a very good set up will result in a fair amount of wasted energy as compared to simply plugging the phone in, which is frowned upon these days. Still, it is fun to tinker with; Marko's thread has a wealth of information to get you started.
I think for charging cell phones; efficiency is (within reason) irrelevant. Cell phones just don't take much power; a typical person consumes about 2 kilowatts total energy on *average* over a total day (>~50 kWh equivalent). A cell phone doesn't even take a watt on average.
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Wireless Power
(With big *thick* litz wire!)