It is not only "how it could be done" but also how it already *is* being done. One commercial bus line in Utrecht, the Netherlands is being charged wirelessly at the end station of the bus line. The driver received some training how to position the bus such that it is aligned with the charging pad, but since bus drivers are already pretty good at positioning a bus at a stop, this was no burden - just a matter of knowing where to place it to make sure that the bus will be charged by the time it is making its next trip. Indeed the bus stop has an embedded coil in the bus bay and the bus has the (resonant) pickup. Buses in the Netherlands also are equipped with ride-height control that allows them to "kneel" at every stop, giving disabled passengers an easier way than to climb in/out the bus - typically the front of the bus is *level* with the curb while the bus is stopped. This no doubt also helps to reduce the distance between charging pad and pickup coil on the bus.
Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: cwa...@proxim.com Private: http://www.cvandewater.info Skype: cor_van_de_water Tel: +1 408 383 7626 -----Original Message----- From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Peter C. Thompson via EV Sent: Wednesday, July 23, 2014 7:40 AM To: ev@lists.evdl.org Subject: Re: [EVDL] EVLN: BMW&Daimler developing 3-Hour Wireless Inductive EVSE for i3 EV Took some digging, but using the phrase "resonant magnetic induction" produce this paper: http://hflab.k.u-tokyo.ac.jp/paper_2010/papers/imura/WEVJ3-2380096.pdf For those that aren't into heavy equations, it shows how you can design coils to absorb resonating magnetic fields over air gaps as large as 200mm with efficiency over 90%. Note that larger air gaps can be acheived with different antenna designs - this will be very useful for larger vehicles (e.g. heavy trucks or buses). Cheers! On 7/23/14, 2:53 AM, George Tyler via EV wrote: > I have done a lot of transformer and inductor design over the years, always > said "you can't focus or direct a magnetic field", apart from ordinary > magnetic materials of course. On day I found something that someone had put > together on the web: He pointed out that if you have a resonant coil in a > magnetic field then the field it creates cancels the field around the > outside, and enhances it in the center on the coil. The effect is just like > "sucking" in the field into the coil! > I can always learn..... > > -----Original Message----- > From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Martin WINLOW via > EV > Sent: Wednesday, 23 July 2014 8:19 p.m. > To: Lee Hart; Electric Vehicle Discussion List > Subject: Re: [EVDL] EVLN: BMW&Daimler developing 3-Hour Wireless Inductive > EVSE for i3 EV > > "Calling Nikola Tesla! Calling Nikola Tesla! Come back! All is forgiven!" > > I bet *he'd* have something to say on this subject! MW > > > On 21 Jul 2014, at 20:24, Lee Hart via EV wrote: > >> From: Peri Hartman >>> Is it possible to use multiple coils to focus the "beam"? >> Magnetic fields are devilishly difficult to direct or focus. >> >> With electricity, we have great conductors (copper, silver, etc.) and > great insulators (air, plastics, etc.) There are *many* orders of magnitude > difference in their conductivity, so we can tightly control where the > current flows. >> With magnetics, we have no good conductors, and no good insulators. It's > as if our best electrical conductor was carbon (which we make resistors out > of), and our best insulator was water (which conducts pretty well, > especially if dirty). Imagine trying to make a circuit work where the > conductors are all carbon, and it's submerged in water, which partially > shorts everything to everything else! >> (Superconductors can give us good magnetic insulators; but they don't work > except at cryogenic temperatures). >>> I don't know wave theory but I believe directional radio transmitters >>> work by having two or more antennas. Can something similar be done with > inductive coils? >> Yes; sort of. Every electric field inevitably has a magnetic field, and > vice versa. That's why we call it "electromagnetics". However, for these > fields to act like waves, which we can focus and direct like light, the > frequencies need to be very high. The elements of a directional antenna need > to have dimensions on the order of 1/4 wavelength or more. >> Wavelength (in meters) = 300 / Frequency (in MHz). At 100 MHz (the > frequency of FM radio and the old VHF television), the wavelength is about 3 > meters -- so a 1/4 wave antenna is about 0.75 meters or 30" long. It's not > too hard to make antennas with multiple elements in parallel to focus and > direct these frequencies (like the traditional TV antennas that look like > giant metal combs). >> At 1 MHz (the AM radio broadcast band) the wavelength is about 300 meters; > thus the tremendously high towers needed to effectively transmit it (the > whole tower is the antenna). It's hopeless to make receiving antennas this > big. We have to use far smaller antennas, that are far less efficient and > require substantial amplification to work. >> The inductive chargers mentioned here are using 85 KHz. The wavelength is > on the order of 3500 meters! It's impossible to direct such frequencies with > the techniques used for radio antennas. >> Vicor makes switchmode converters that operate just over 1 MHz; about the > highest practical frequency for state of the art switchmode converters. They > had to go to heroic lengths to get their transformers to operate with > reasonable efficiency (90%). Such frequencies are not yet practical for high > power converters. >> Lower frequency transformers are more efficient. Conventional 60 Hz > transformers can be over 99% efficient, if you use enough copper and iron. > But to do so, they require *very* tight coupling between the primary and > secondary -- minimal gap between them. This is the opposite of the > requirement to have some separation between primary and secondary as imposed > by the wireless charging proponents. >> I think the only way to make a practical "wireless" charger will be to use > more or less ordinary frequencies, and mechanically position the primary and > secondary coils as close as possible. This means either moving the car's > secondary coil or the charging station's primary coil so they touch. >> -- >> Excellence does not require perfection. -- Henry James >> -- >> Lee A. Hart http://www.sunrise-ev.com/controllers.htm now includes the >> GE EV-1 > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA > (http://groups.yahoo.com/group/NEDRA) > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) > > _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
