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From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: A couple of problems with EV charging roads?
Date: Sun, 02 Jun 2024 10:51:11 -0700
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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!