Air Coupled EV Charging

ote:

y sort really. They have a video that compares their 10 kW system to the " standard" 3.3 kW system. I've never seen a 3.3 kW L2 charger. That would be 240 volts, ~15 amps. The lowest I've seen is about 7 kW. ...

hybrids are ~2kW.

use.

use.

ly work up to those levels (3.3kW or less) even if the EVSE advertises high er capability.

ower is constant at the maximum rating until close to the end of the charge .

on the Pilot line. The charger internal to the vehicle only consumes power up to that amount or to its internal limit.

John is confused...

But then you saw that coming, didn't you?

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  Rick C. 

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gnuarm.deletethisbit
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If the coil has an inductance and is driven by a sine wave voltage at some frequency, the current is defined. We don't know or care what's inside the black-box amplifier.

The current into the coil will of course be mainly reactive until this coil magnetically couples to some load. Like a nearby beer can maybe.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

Rerod, dirt, house wiring, car body, 6-packs of whatever, washing machine, bedsprings in the room above. It's like Tesla's scheme to broadcast power everywhere.

Hey, a neighbor could put a tank coil in *his* garage and steal your power. Or sue you if his dog gets cancer.

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John Larkin         Highland Technology, Inc 
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John Larkin

On Monday, 25 March 2019 15:44:00 UTC-7, John Larkin wrote: ...

...

It will be largely reactive even when coupled because of the large leakage inductance.

EV wireless charging systems have 'Foreign Object Detection' so that they w on't energize at high level until communication with the vehicle is establ ished and the losses are within expected limits - it should not energize wi th a beer can or other piece of metal in the field.

They also have proximity detection to disable the high magnetic fields if n on-metallic objects (such as pets or people) are close to the high-magnetic field region.

kw

Reply to
keith

This isn't a Tesla idea. Why do you hate Tesla so much that you project all EV matters onto Tesla?

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Reply to
gnuarm.deletethisbit

e inductance.

won't energize at high level until communication with the vehicle is esta blished and the losses are within expected limits - it should not energize with a beer can or other piece of metal in the field.

non-metallic objects (such as pets or people) are close to the high-magnet ic field region.

Another video I saw at the company's web site shows them holding a cell pho ne in the field without being affected. Also the person's hand.

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gnuarm.deletethisbit

On Monday, 25 March 2019 15:51:34 UTC-7, John Larkin wrote: ..

...

Err, no.

The ferrite cores used ensure that the field drops off within a few centimeters. There are health safety limits that ensure that the field that can be accessible to a human (or other animal etc) is is very low.

The field would be negligible at a neighbor's house and it would only be active when the car is actually charging.

The receive to transmit coil distance is measured in single digit cm - if there is no car there to communicate with the transmitter or any leakage etc is detected the energization is disabled.

kw

Reply to
keith

The coil will spread the field, but resonant action pulls it in

And, it's not about the current in the coil, but rather that you create a resonant circuit, so that the leakage inductance is not in play (reactive power). The capacitor is essential. Read up on resonant WPT. Search the APEC/IEEE papers, you'll get it then

Cheers

Klaus

Reply to
klaus.kragelund

No, it's not. It is actually directed somewhat since ferrite is place on the back of each coil

Nope

When you are further than 10 times the diameter of the coil the field is low

Cheers

Klaus

Reply to
klaus.kragelund

A couple of years ago there was a paper at APEC (APEC-conf.org) investigating the effects on humans and animals. Conclusion: no real danger

Cheers

Klaus

Reply to
klaus.kragelund

Q is simply whatever you let it be.

A low Q will transfer very little power at less than modest k. You need Q >= 1/k, roughly speaking.

That means for a given power transfer at high efficiency, you need quadratically (cubically? worse?) higher Q with respect to distance.

For the same power transfer, that means Q times more reactive power. The coil gets massive, fast.

Tim

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Reply to
Tim Williams

Because it gets hot (or not).

Also, something about harmonics, or the apparent complexity (apparent in terms of, say, cost?) of the system.

You can make a sine wave directly, and handle all the reactive power in a linear power amplifier; but the efficiency goes as 50% / Q. The box gets stupendously hot.

You can direct drive it, but the harmonics will be apparent, and the efficiency will be, say, 70-90%, but not 98%. Or with a multilevel inverter, the steps will be less apparent (and even easier to filter), but the design will be far more complex.

Or you can direct drive a tank, which is tuned with a capacitor, and doesn't get hot, and has a circuit simple enough an undergrad can build one*.

(*I first demonstrated a 1kW variable frequency induction heater back then.)

Other quirks: how the tuned frequency varies with (complex valued!) load. If it responds like a passive tuned circuit, well, there's that. If it behaves stepwise, they may be switching capacitors to keep frequency within bounds (this is probably how an ISM band wireless power system would operate -- a power cap DAC).

There are of course many other possibilities in design and behavior space, but the further out you go, the exponentially less likely you get.

Tim

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Reply to
Tim Williams
"

This isn't a Tesla idea. Why do you hate Tesla so much that you project all EV matters onto Tesla? "

I think he is talking about Tesla the (old) man, not Tesla the car company.

Reply to
edward.ming.lee

The recurring pattern is that someone rediscovers resonance, takes out

10 or 20 patents, makes fuzzy claims, raises 10 or 20 million dollars, and disappears. It happened for cell phone charging and now for cars. The usual claim is that the resonant coupling works at great distances. Investors seem to like it; maybe they are thinking of tuning forks and violins.

It's just impedance matching. If it makes near-field loop coupling easier, fine. But it's not going to be anywhere as efficient as a simple connector.

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Reply to
John Larkin

I wouldn't recommend using a linear amp to charge a vehicle.

Class D isn't hard. It approaches 100% efficiency into any load, because ideal switches are lossless.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

If you've got 100V and 100A in the coil the the driver runs off 10KW input there's a fair chance that it's resonant.

resonance is just an effective way to pile VAR into the coil, it's not the only way, you could use 100A 100V drivers, and flyback diodes, to recover the immaginary power - you save money by not needing bipolar capacitors, but loose on the large switches and diodes needed.

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Reply to
Jasen Betts

Yep, but that's NOT the case. The coil is resonated, the drive into it is class C, and the current is NOT defined, so it can climb until the power transfer to the battery is adequate. What power engineering sense would it make, to drive sine wave voltage (low impedance) into a resonant LC circuit?

Low impedance voltage source is BAD engineering. Design it like you want it to WORK.

Reply to
whit3rd

The driver has to be low impedance somehow, or efficiency would suck.

The final system in a near-field coupler must be low-Q, because we're sucking kilowatts out of it. Resonating might have small routine advantages in a low-Q system to improve matching a little. Most of the money-raising claims for resonance are to allow distances between the transmitter and the receiver, which allow low coupling and high Q. And heat everything else in the garage.

Well, I've done magnetic coupled power. Have you?

What waveform is actually used in inductive car chargers? I'd think that a softened square wave would make sense on both ends.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

There is something about coupled resonant circuits.

First of all, if you pump power into a resonant circuit, the oscillating field keeps growing until something in the vicinity absorbs as much power as you are pumping into it. (Or until something breaks.) In a simple-minded LTspice simulation (below), I even found that *more* power can be transferred as the coupling gets weaker!

And most of us will know about dip meters, where the energy drawn from an oscillating field will peak when a resonant circuit is coupled to it. Think of it as a form of impedance matching, where most of the power goes into the load that is properly matched.

Jeroen Belleman

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SYMATTR Type ind SYMBOL cap 48 128 R0 SYMATTR InstName C1 SYMATTR Value 159.15n SYMBOL current -144 128 R0 WINDOW 123 24 108 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName I1 SYMATTR Value SINE(0 1 100k) SYMATTR Value2 AC 1 SYMBOL res 496 96 R0 SYMATTR InstName R1 SYMATTR Value 10 SYMBOL ind2 336 112 R0 SYMATTR InstName L2

SYMATTR Type ind TEXT 56 312 Left 2 !.tran 1m TEXT 184 40 Left 2 !K12 L1 L2 0.1 TEXT 56 352 Left 2 !;ac dec 1k 50k 200k

Reply to
Jeroen Belleman

The Q better be quite low, otherwise there are huge voltages (across the capacitor) and huge currents (through the coil). After all, we are talking about similar RF powers as US medium wave ("AM") broadcasting stations (50 kW).

Reply to
upsidedown

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