Re: A couple of problems with EV charging roads?

On 3/06/2024 3:51 am, john larkin wrote:

On Sun, 2 Jun 2024 12:32:25 -0500, Crash Gordon <uucp@crashelex.com>
wrote:
 

I've seen a couple of articles about roads with embedded inductive
charging for EVs.  And there are a couple of issues that seem to me to
make these roads unfeasible.  (I'm not even going to get into any of the
financial side)
>
My qualifications:  I have a few decades experience in circuit design
and have had the word "Engineer" in my job title at several different
employers, but never went to college.  So I have a lot of
"wisdom-through-experience" but there are a lot of holes in my basic
knowledge -- I tend to know a lot about the things I know, but nothing
at all about other closely related things.  So I am quite willing to
accept that there's stuff going on here I simply don't understand.  Feel
free to educate me.  Moving along...
>
>
First: Inductive charging is basically building a transformer where the
primary is in one device (in this case, the road surface) and the
secondary is in a different device (here, an EV).  Ordinarily when we
design transformers, we take great care to maximize the coupling between
the primary and secondary because loose coupling is responsible for much
of the loss in transferred power.
>
But in charging an EV there is necessarily going to be a considerable
air gap between the primary and the secondary.  Although we can optimize
in other areas to account for this somewhat, it seems to me that there's
going to be a lot of energy lost here, mostly as heat radiated into the air.
>
Second: In order to transfer significant energy, there's going to have
to be some significant coupling of magnetic fields between the EV and
the road.  Wouldn't this be a source of substantial drag?  Effectively
the car would be driving "uphill" the whole time it's charging.
>

 I'd expect that drag to be small. But if the car drops down a coil, to
be closer to the roadway, air drag will increase.
 

>
My thought is that if we're going to be shoveling huge amounts of
electricity into a road surface, we could use it more efficiently by
building a giant linear actuator with the EV as the moving part.
>
>
Opinions?

 It's a silly idea. The cost would be incredible. And we're eliminating
power plants and working towards rotating blackouts already. Imagine
adding a megawatt per mile of road.
 Resonant coils can couple fairly well, even with an air gap. I think
some electric busses charge that way.
 Efficiency will be low. Some of the transmitted energy will heat the
soil and rerod and car parts. And melt snow!

John Larkin seems to be just as ignorant as Crash Gordon.
Varying magnetic fields only transmit energy when they induce current in the soil, snow and reinforcing rods (which aren't a feature of most road construction). Car parts might be a problem, but a car isn't designed to be a Faraday cage, and probably won't present the sort of current loop which could pick up much energy from the charging field.
Electric buses recharge by parking on top of the coupling loop. We haven't had any stories about cars parking or waiting briefly on the same spots and getting hot - the charging hardware presumably has a bus sensor and turns off when there isn't a bus there to charge.
In-road chargers will presumably be just as smart.
--
Bil Sloman, Sydney