Air Coupled EV Charging

And how can a power transformer that big run at 80KHz? Doesn't that require a small number of turns, and can that be efficient?

I understand resonance. I don't understand how it can be efficient charging a car at any distance. The field will be all over the place. Better hope there's no rerod in the floor or damp dirt underneath.

People keep discovering the miracle of resonant charging. I think even MIT got some press on that.

More efficient? Do you mean less labour is involved? there's no way that it's more energy efficient than a plug.

I agree, their numbers have to be in error -- maybe made up for the investors? No need tho, they could be 10% worse and still have a good set of customers.

Not until i figure out what to do with the metal after warrant expired. I won't be able to get parts for repairs, or even helps to fix problems. I walk pass a Tesla showroom all the time. Nice looking car, but at a distance.

Wondering if they are keeping the SF Van Ness Tesla open afterall.

At a much higher voltage. You do see arcing pretty frequently, which erodes the feed wire and the sliding contact, and generates radio-frequency interference.

Why would you care about the charging time??? Once you get where you are going you can let the car charge while you aren't diving it. What are you trying to say???

There are better charging options. The cool part is that you can charge at home at a much lower cost rather than drive to a filling station, wait in line, deal with a messy, smelly petroleum product and pay more money.

Rick C.

Cars spend 95% of their lives parked. That makes a nineteen to one recharge to discharge ratio the upper limit of what is practical. Two to one is fine.

Me? My car??? You don't want to know what I paid for this car. The subsidy had nothing to do with it.

I bought this car, at the time I did, because I didn't want to wait any longer so I could drive it to a wedding. lol

Rick C.

ositioning a car?

Ok, I guess the company is lying then. They say EV charging with a cable i s 93% efficient and their solution is 96% efficient. I don't know what exa ctly they are counting in that comparison, but if it's not apples to apples , they will get ratted out very quickly.

I do know the connector to the car gets very warm on Tesla Superchargers. The present chargers will provide up to 120 kW. To get to 200 kW it seems they liquid cool the cable. They can't provide half inch bus bar in the fi nal cable. The cable has to be something you can actually pick up and plug into the car. That's a limiting factor.

The focus of this particular product seems to be taxis and buses. The emph asis is charging while normally paused to pick up passengers. For a car 75 kW is about 300 MPH added to the range. If the vehicle is driven at an av erage speed of 30 MPH, the charging time can be 1/10 the driven time. In O slo it seems they have taxi queues where they are employing this. The driv ers seem to prefer it in the trials they've done because they don't need to waste time refueling.

The installed price is $8k for 75 kW. If they had a lower priced 6 to 10 k W home version I would go for it. The speaker points out that it will be k ey for the car makers to be on board and not consider the wireless installa tion to void the warranty.

Rick C.

Now you are just making up stuff. Why not do a little reading or maybe eve n write the company and find out how they calculate the efficiency number? I am pretty sure it isn't a made up number. If they put that in the offic ial company info and it's BS, that's securities fraud.

Rick C.

OK, point taken, but 98%. I'm sorry, but having taken too many tricky inaccurate measurements close to 100%, no, I don't believe it. But I'll ask.

Not 98% that I saw anywhere. In the video the guy claimed using a cable wa s 93% efficient and made it sound like this was the total losses in the cha rging unit because this is the "operator's losses" "taking 100 kWh from the grid and delivering only 93". He goes on to claim their efficiency is 96% . 10 minutes into the previously linked video.

I don't see anything on their web site. No facts or figures of any sort re ally. 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 vo lts, ~15 amps. The lowest I've seen is about 7 kW. Still... wireless is a very desirable feature as long as it is not *worse* than a cable. The com pany the speaker is with seems to be fortum.com which also has no info on t heir web site for this product. I guess they are still in the early stages and don't have Elon Musk running the company.

Rick C.

It is a matter of flux coupling, and resonance improves the effective coupling constant. If you need to voltage-convert and current-limit and rectify, why not magnetic coupling?

In a conventional, no-tuning transformer, with low coupling, energy stops at the primary; in resonant windings, it has Q chances to get into the secondary before it is lost.

what numbers?

Any idea what ISM band is used ? 6.8, 13.6, 27.1.or 40.7 MHz ?

Just wondering how much spurious emissions these devices spews out, causing harm to radio traffic in HF and VHF bands. Fortunately the ISM bands have a harmonic relationship, since such installations will generate a lot of harmonics from the devices itself or from any rusty bolts at those power levels.

The IEC standards also define how strong fields any humans should be subjected to, being 28 V/m for 10-400 MHz. Since this near-field, also the RF currents must be considered.

If the taxi driver is sitting in his car waiting for the next job while the car is being charged, is he subjected to stray files greater than the standard allows ?

Why would the DC charging efficiency be that bad, unless you include the whole chain from mains into the accumulator.

The fast charging station efficiency should be quite high. Just take a one or two transformers transforming the medium voltage (MV) line voltage (typically 14 or 20 kV) into a few hundred volts so that you get 400 Vdc after rectification. Use zigzag secondary or two transformers (wye and delta) and feed it to 12 or 18 pulse rectifier, thus no need for PFC. If be input voltages varies greatly, use SCRs as rectifiers and control firing angle. A big transistor is required to switch off the DC current, but the rest is low power electronics. Of cause any charging control in the car will reduce the total system efficiency, but the same applies o RF charging. Apparently the 96 % RF just contains the RF coupling efficiency, not the full system efficiency.

Win suggested 80kHz may be typical.

Doubt they're using ISM, that makes things harder. Harder inverter, costlier coil, tighter filtering to keep harmonics down, active tuning (ISM bands are quite narrow), etc.

Probably around nothing. It's a standard induction heater, with slightly different tuning control if the secondary is tuned, and an on-off control so it's not transmitting all the time, just weakly pulsing until it detects a load.

So, a big induction cooktop, actually.

Not terribly hard to filter, the nearest harmonics will be a little tricky but not insurmountable. Picking an operating frequency below 150kHz helps with that; picking a 3rd harmonic below that would help even more.

Nah, wrap it with ferrite plates. You need to anyway, just from the basis of not melting the thing to pieces (induction heating of the housing).

When it's open, it's pulsing weakly, or there's another detection mechanism (wouldn't surprise me there's some IoT shit in there for logging the car and authorizing use) locking it out, so no worries when open.

Tim

Then they are using simple inductive coupling, not near field wireless power transmission like NFC.

Fine if the EM radiation is very low outside the charging station, then any frequency cold be used. However, if it spreads out in free space, then some ISM band must be used.

At frequencies below 1 MHz 87 V/m would be allowed.

Yes putting the car and driver into an induction heater :-).

In Europe, the long wave broadcasting band starts at 153 kHz, so you would have to put the frequency below 50 kHz.

Certainly there would be some detection if a car is above the coil or not, just to avoid heating the coil losses when no car is above.

That statement hasn't contradicted anything... :-)

NFC is what, 13.56MHz innit? So it's near field until a good, what, several meters away?

It's simple inductive coupling. :-)

All that varies is whether you really need tuning on the secondary at all (preferably not, but not so reasonable at, say, k < 0.5), or if so, how much; and what Q the coils need, which goes up...cubically? with distance.

Litz cable gives a Q up to 1000 or so, which for that matter would still be challenging to meet with ferrite shields in place, even with good quality ferrite.

More would be possible with superconductors (including shields). I wouldn't put that past them either, I guess. But that introduces considerable costs, and also... how do you supercool the receiver coil? :^)

Yeah, same here more or less, FCC Part 15 starts at 150kHz.

These would probably be industrial actually (FCC Part 18, or probably... CISPR 11?), unless because of where they'd be installed, they have to be 15. You can get away with a lot there; I haven't even seen an industrial induction heater* with a line filter built in(!).

Tim