Wireless recharging for battery powered 'buses

[jamespetts]

I thought that some people might be interested in an article about some new experimental 'buses in Milton Keynes on the BBC website.

[ӔO]

I wonder why they decided on inductive charging over a direct connection socket or overhead wires?

[jamespetts]

I suspect because residents tend to object to overhead wires as spoiling the view (and they are probably more expensive to erect), and a direct connexion socket would be more labour intensive, requiring plugging and unplugging at the end of every route, and would also thereby reduce turnaround speed.

[ӔO]

Apparently it is 80% efficiency at 1cm and 60% at 12cm (+30cm underground), so I don't think the long term costs would be cheaper than overhead.
However, that's a lot more efficient than I was expecting it would be, considering how sensitive Qi chargers are

[Ters]

Reminds me of an old (20 years or so) Uncle Scrooge comic where Scrooge launched a project of replacing all cars within a city with autonomous, inductively power cars. I think I've read about some of the other similar projects at the end of the article, or if not, some other idea/project, providing inductive charging for all vehicles.

I wonder why they decided on inductive charging over a direct connection socket[...]?

I picture buses driving around with a long extension cord. But everything from toothbrushes to mobile phones use inductive charging, and the former have so for some time. I'd say it makes more sense for something that moves and can't as easily be plugged in.

[Lmallet]

Interesting idea, they use the wait time at the end of a route to charge for a few minutes.  I wonder if the buses can skip the charge if they are running late, or if they absolutely need to stop for a set number of minutes.

[Markohs]

I wonder if the extra magnetic energy and static energy probably generated by this mechanisms can affect passenger's health, or damage their electronic devices (phones). Getting some extra battery power on your mobile phone for free whould be cool through.

[Ters]

Well, I've seen mobile phones affect 10000+ volt appliances more than the other way around. It could be interesting if passengers with metallic objects on them (buttons, piercings, medical implants) got pulled to the floor everytime the bus passed over a charging station. It would be the end of the system very quickly. But I think the magnetic field would get blocked by the floor of the bus, and mostly confined between the sender and receiver, so you'd probably have to crawl under the bus to get affected in any significant way. I can't at the moment find any numbers for comparing magnetic chargers against other magnetic fields surrounding us.

[prissi]

The stray filed depends on the air gap (and hence more stray field less efficiency). Passenger on the bus will not get any field at all (Faraday cage), at least if the bus is mainly made of steel (which is so far the most common case).

Since people are allowed to make NMRs which use much stronger fields (>4 Tesla) without nay side effects (apart from magnetic parts on or in the body), the effect of these low frequency fields is neglible.

[sdog]

The buses lower the secondary coil, to nearly touch the ground, that might be exactly what's needed. Question now is, how deep is the coil burried and properties of the medium it is buried in.

A 30% efficiency loss while charging, might still be better than carrying more battery mass on the route. Especially when looking at life-cycle-costs of Li-Ion batteries. Overhead wires always have the difficulty of connecting to them properly. For the short stretch that is needed for charging the stationary bus, overhead rails could be used as well. Such a gantry can't be expensive to build, maintain, (defrost...) and can't be much more ugly than a bus-stop or traffic sign.

Stray fields should not be a safety issue: It is easy to safeguard that the transmission only happens when the secondary coils is placed in the correct position of the primary coil. Frequencies for such power transmissions are low. Field strength is greatest within the circumference of the coils, and quickly drops of outside. The bus above the coils prevents people from getting to close, and being mostly metal shields quite well.

Here's Bombardier's product page:
http://primove.bombardier.com

unfortunately, i haven't found any specs there.