How is this possible

mivey

Senior Member
It is possible because energy does not travel inside the wire but in the surrounding electromagnetic field. All we have to do is to get the field to interact with a device across the gap to induce a current. Through induction we can create a current and voltage on the other side of the gap. Once we have a current we have a magnetic field. Once we have the voltage we have an electric field. When we have both fields, we can then exchange energy.

A transformer uses that principle to exchange energy across the gap. A radio also uses wave energy except the EM wave leaves the antenna and propagates through the air without the wires to act as a guide. When the EM wave crosses the crystal in the radio, the crystal oscillates and we create a voltage and current inside the radio to hear the information delivered in the radio wave. We actually extract some energy from the radio wave.

The charger could use a gap like a transformer or it could send an EM wave but I'm not sure which it is doing. I suspect it is induction like a transformer since that would be more efficient.

PS: I covered energy travel in the EM wave in a thread a while back but I don't remember the thread.
 

mivey

Senior Member
Yeah, that's it.

To skip the technical and to not re-hash the other thread, we can just use common sense: energy can travel across the gap in a transformer, energy is transferred via inductive heating when we separate conductors in metals pipes and through metal box entries, radio waves transmit energy, microwave ovens transmit energy in waves, and the list goes on.

Using common sense, we can see that we do not have to have a metal-to-metal connection to transmit energy across the gap and charge the vehicle. What is really cool is that they can do this with an acceptable amount of efficiency across such a big gap. I may take some time to read up on what they are doing with the Volt.
 

mivey

Senior Member
I may take some time to read up on what they are doing with the Volt.
Well that was quick:
"The Plugless Power EV charging system uses a centuries-old concept called inductive power transfer ? the same technology used in both household products and electrical transformers around the world. Using magnetic fields, energy is transferred from the transmitting coil in the parking pad and converted into an electrical current by the receiving coil in the vehicle adapter."

So it is just an air-gap transformer. And they are claiming they will have better than 90% efficiency with the residential models. Pretty neat.
 
Well that was quick:
"The Plugless Power EV charging system uses a centuries-old concept called inductive power transfer ? the same technology used in both household products and electrical transformers around the world. Using magnetic fields, energy is transferred from the transmitting coil in the parking pad and converted into an electrical current by the receiving coil in the vehicle adapter."

So it is just an air-gap transformer. And they are claiming they will have better than 90% efficiency with the residential models. Pretty neat.
I agree, way cool!

Just the other day I was thinking about what a bummer it would be if you forgot to plug your plug in only car. I can't even keep my phone charged all the time. I can see how easy it would be to forget to plug the car in. With the cordless charger, that's not a problem.

We already have electronic devices that have cordless chargers. You just place them on a mat.
 

mike_kilroy

Senior Member
Location
United States
I can see how easy it would be to forget to plug the car in.
Actually, once you have a 100% electric car you NEVER forget to plug it in. Not a forgettable thing; very similar to watching that darn charge gauge CONSTANTLY while going someplace. It becomes totally automatic to plug in - even before opening the door for your wife to get out.... I know.....

I wonder how they can get 90% efficiency over 6" inducing 230v@30 amps..... that's a lot of power.
 
Actually, once you have a 100% electric car you NEVER forget to plug it in. Not a forgettable thing; very similar to watching that darn charge gauge CONSTANTLY while going someplace. It becomes totally automatic to plug in - even before opening the door for your wife to get out.... I know.....

I wonder how they can get 90% efficiency over 6" inducing 230v@30 amps..... that's a lot of power.
And I wonder what happens to the cat or dog that goes under the car while charging. Or any loose metal objects. That's gotta be a strong and large magnetic field.
 

mike_kilroy

Senior Member
Location
United States
remember the stink years ago about the fields from electric blankets? Or the dead cows under the hi power lines? Wonder who will start THAT worry again when it catches on?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
If this must be 6" from the transmitter to the receiver I am assuming there is a mat on the floor. This means the receiver is only 6 inches off the ground. That is way to low. I am assuming it is not something you must constant move around. I guess the mat could be built up so the device is higher. When I read it I skimmed it and thought it was under the hood and I was trying to imagine this going thru the hood.
 

mike_kilroy

Senior Member
Location
United States
WiTricity

WiTricity

Guess there is a lot going on in engineering that we don't keep up with! Amazing stuff based on stuff we already know but never had reason to experiment with in such a way.... Check out WiTricity (http://en.wikipedia.org/wiki/WiTricity):

The term WiTricity was used for a project that took place at MIT,...The researchers successfully demonstrated the ability to power a 60 watt light bulb wirelessly, using two 5-turn copper coils of 60 cm (24 in) diameter, that were 2 m (7 ft) away, at roughly 45% efficiency.[4] The coils were designed to resonate together at 9.9 MHz (≈ wavelength 30 m) and were oriented along the same axis. One was connected inductively to a power source, and the other one to a bulb. The setup powered the bulb on, even when the direct line of sight was blocked using a wooden panel. Researchers were able to power a 60 watt light bulb at roughly 90% efficiency at a distance of 3 feet. The research project was spun off into a private company, also called WiTricity......In April 27, 2011, car maker Toyota made an investment in WiTricity.

Key thing seems to be higher freq and resonant coils to catch 90%+ of the field!

my old vette has less than 5" clearance; the electric equinox conversion is probably 6" to the batteries too....

As a young kid of 12 I lite up a 4 foot florescent bulb for friends a foot from my Heathkit 200watt 40 meter dipole in my attic.. sure wish I knew how to spell patent back then.
 
Last edited:

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
And I wonder what happens to the cat or dog that goes under the car while charging. Or any loose metal objects. That's gotta be a strong and large magnetic field.
But it's oscillating, so loose ferromagnetic objects nearby might vibrate a little bit, but they won't get tossed around. Single coil electric guitars through high gain amps might have a problem, though. :D
 
Guess there is a lot going on in engineering that we don't keep up with! Amazing stuff based on stuff we already know but never had reason to experiment with in such a way.... Check out WiTricity (http://en.wikipedia.org/wiki/WiTricity):

The term WiTricity was used for a project that took place at MIT,...The researchers successfully demonstrated the ability to power a 60 watt light bulb wirelessly, using two 5-turn copper coils of 60 cm (24 in) diameter, that were 2 m (7 ft) away, at roughly 45% efficiency.[4] The coils were designed to resonate together at 9.9 MHz (≈ wavelength 30 m) and were oriented along the same axis. One was connected inductively to a power source, and the other one to a bulb. The setup powered the bulb on, even when the direct line of sight was blocked using a wooden panel. Researchers were able to power a 60 watt light bulb at roughly 90% efficiency at a distance of 3 feet. The research project was spun off into a private company, also called WiTricity......In April 27, 2011, car maker Toyota made an investment in WiTricity.

Key thing seems to be higher freq and resonant coils to catch 90%+ of the field!

my old vette has less than 5" clearance; the electric equinox conversion is probably 6" to the batteries too....

As a young kid of 12 I lite up a 4 foot florescent bulb for friends a foot from my Heathkit 200watt 40 meter dipole in my attic.. sure wish I knew how to spell patent back then.
Shades of Tesla!!
 
It is possible because energy does not travel inside the wire but in the surrounding electromagnetic field. All we have to do is to get the field to interact with a device across the gap to induce a current. Through induction we can create a current and voltage on the other side of the gap. Once we have a current we have a magnetic field. Once we have the voltage we have an electric field. When we have both fields, we can then exchange energy.

A transformer uses that principle to exchange energy across the gap. A radio also uses wave energy except the EM wave leaves the antenna and propagates through the air without the wires to act as a guide. When the EM wave crosses the crystal in the radio, the crystal oscillates and we create a voltage and current inside the radio to hear the information delivered in the radio wave. We actually extract some energy from the radio wave.

The charger could use a gap like a transformer or it could send an EM wave but I'm not sure which it is doing. I suspect it is induction like a transformer since that would be more efficient.

PS: I covered energy travel in the EM wave in a thread a while back but I don't remember the thread.
The greater the airgap is the greater the losses are. Thta is why high efficiency motors - rotating transformers - have ever decreasing airgaps between the stator and rotor and why contactor armatures have highly polished mating iron surfaces.
 

mike_kilroy

Senior Member
Location
United States
That was my initial thought also, but after reading the references I posted earlier about how MIT transferred power over 2 meters at 60+% eff, and over 1 meter at 90% efficiency - due to 10mhz freq & tuned resonant coils, I have come to the conclusion that 6" is nothin' and no c0il dropping is likely required!
 
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