# Inductive (In Floor) Recharging



## Woodsmith (Jun 5, 2008)

It would require a lot of infrastructure and standardisation both in componants and in parking bays. Many drivers can't park in the centre of a bay because they are bad at parking or because they are stupid and park across two bays or at a silly angle blocking three bays.

There would need to be safety checks so that two or three charging coils don't energise together for the one car.

Have you checked for the effect of that charging process on people with pacemakers? Also the magnetic effects on credit card strips, bits of metalic refuse on the road surface and metal body parts in people? How about noise and vibration from ac hum?

These were the sorts of things, and others, I was requested to examine for a thesis proposal I was working on a couple of years back when the ground loop induction charging process was a part of the proposal.


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## rankhornjp (Nov 26, 2007)

They have a similar system for go carts (not inductive tho). A set of spring loaded contacts are attached to the bottom of the cart with durable brass conductors. They contact raised metal plates in the pit area that completes the circuit when the cart enters the pit and stops over them for five seconds. It is hooked to a smart charger that only charges the needed amount of energy then shuts off automatically. When a cart is not over the plates, the unit stays off, saving energy. The metal plates are raised so that the contacts don't touch the ground when the cart is in motion. You would still have the issues of bad parking, but it wouldn't work it you weren't parked correctly. It would be like putting the charge connectors on top of a speed bump that is in the parking spot. With the right charger you would eliminate the need for the packs to be universal and you could retro-fit the system to just about any car....


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## dataman19 (Oct 7, 2009)

rankhornjp..
Interesting points... But we already considered this and have issues with liability. In fact we have issues with liability with both indusctive, reactive and direct electrical charging interconnects...
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Until Congress extends the Liability Waiver to After-market cahrgers we will continue to stumble around this liability issue. Anything that is intended for public use must be idiot proof. An absolute must!
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If some idiot places two coat hanger wires across the terminals and then attaches them to his portable stereo, energizes the charger with the intent of powering his stereo while he Tailgates at the Mall, Stadium or whatever - Should he electrocute himself - the operator of the charger along with the owner and the Manufacturer could be held liable....
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We live in a world of stupid and ambiquous laws, and live in a society that prey upon the corporate world (not that all the corporate greed has gone un noticed by the common people). The legal arguments are always in favor of "Why didn't You plan For This" instead of "What was that stupid person thinking?".
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No matter if the charger is intended for your own personal use, the use of a Co-Op or the use of an exclusive club - it should be idiot proofed. And it should be locked away so that an idiot cannot defeat the safeguards.
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Which brings up the ultimate quandry: If you build a charging station for EVs that is intended for Public Use - How do you keep the malicious criminals, the vandals, and the relatively challenged stupid people from messing with it?
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We need a public network of charging stations. But the only ones covered by the Federal Liability Exemptions are: A) Public Utility Providers (ie: the electric companies) and B) National Automakers (protected from liability and missuse of products manufactured for use in their end product - ie: their cars, trucks, EVs). Everyone else is fair game for the legal buzzards.
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Two years of Law School Taught me enough to make me not want to be a lawyer. Phycology wasn't that interesting after two years either. Engineering and Technology was what I stuck with and after 24+ years of Government Service I am now into Alternative Energy and Bio Fuels Research.
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If the Investors quit quibbling about the pennies being spent and stick to their promise of total funding - we will soon launch the first national after market EV car company. But then again - those darn lawyers and Wall Street babies keep chiming in and fouling up the funding...
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Dang... Stupid people (and even educated Stupid People)- they are all driving us crazy..
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Dataman19


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## dimitri (May 16, 2008)

I'm sure you know that production EVs in the 90s had inductive paddle chargers. Same principle, except the paddle had to be inserted in the car. This provided safety by not exposing any contacts. 

However, for inductive charger to be efficient, both parts have to be as close as possible, practically touching each other, because losses are exponential with the distance. In your example of a floor integrated inductor and the other part on the bottom of the car, even a 4 inch clearance will make it useless from efficiency perspective.

Add to this requirememt of perfect horizontal plane matching and you are in a world of engineering troubles.

Sorry to be pessimistic, but with recent approval of standard EV connector SAE J1772, I just don't see anything else being adopted.

http://en.wikipedia.org/wiki/SAE_J1772


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## samborambo (Aug 27, 2008)

This is a practical inductive charger system implemented about 45 mins from where I live: http://www.ipenz.org.nz/IPENZ/Forms/pdfs/TreNZ1.pdf

It charges low speed people movers around a geothermal park. 7 minutes is enough to replenish 2kWh for the next trip around. They're using pretty standard LA cells and getting close to 3000 cycles by means of high current pulse charging.

The system uses many secondary pickups to charge groups of cells to keep the pack reasonably balanced. It's somewhat close to an active cell balancer.

I still haven't been down to check it out yet although it looks very interesting.

Sam.


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## Woodsmith (Jun 5, 2008)

When I looked at a practical way to impliment it I figured the road coil to be a flush plate that can be driven over and a movable coil under the vehicle that was lowered to the road when charging was required.


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## MJ Monterey (Aug 20, 2009)

Dataman,

Great concept, I am a bit ignorant but please educate me (yes I am open to it)

As an add-on to the side affects concerns/scenarios to consider (these are not intended to be negative or tear apart your concept, think of them as FAQ type questions, remember I am ignorant). 
What are the potential affects on surgically implanted steel pins?
Potential affects to persons using walkers and wheel chairs?
Potential affects to hearing aids and other electronic devices?
Can I sit in my car and do work on my laptop safely while charging during lunch?

On to the constructive concepts.
Could you size this to fit into a standard in ground utility box (if such a thing exist)? this would make service and upgrades more practical than digging up the parking lot

Can the grid side coils (do you have a good term for this?) be small enough so that they can move on an xy carriage system underground to better align with the receptor pad

Have you looked at the potential for a drop down receptor pad? If the distance between pads has an affect on efficiency, this may be a nice added option for higher efficiency charging.

Added option for the purchase agreement network handshaking procedure. Can you allow for a "please do not charge right now" or ability to decline service (if $/kWh is to high) option?. Scenario1: I am a short distance from home and can recharge more cost effectively at home. Scenario2: I have regen capabilities and will be going down hill from the parking spot for a while and my battery is mostly full. True the vehicle should not be in a charging spot if not charging but we both know it will come up.

I do have a real life experience with utilities under a cement slab. A house I owned a while back had the plumbing run in the fill gravel under the cement slab floor. The expansion and contraction of the copper pipe abraded small pinhole leaks in the plumbing. So if you opt to put the grid side coils under or in the slab, consider a molded plastic housing and spec the materials that the housing is placed in.

I will roll the concept around abit more and look forward to more discussion.....


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## Tesseract (Sep 27, 2008)

I love this idea... actually, a minor variant of it... resonant charging with negotiated frequency of operation.

Dimitri - it solves the problem of needing the primary and secondary to be as close as possible, as in a regular "transformer"... the resonant variation uses the same inductive loop in the floor/parking lot but adds a variable capacitor to form a resonant tank. The "transmitter" (ground coil) and "receiver" (in the EV) negotiate the frequency necessary to maximize power transmission efficiency and the best thing is that the two coils don't need to be perfectly aligned and close to each other to achieve very high efficiencies.

A somewhat cheesy website that promotes commercial applications of one version of this technology is: http://www.ecoupled.com/resourcesMain.html

Normally I would not mention such a website, but their technology has actually made it into a few products, one of which I saw a demo of at a local Best Buy (the "Universal Pad").

Now, the problem with this interfering with pacemakers and such is no red herring - resonantly coupled power transmission could really do a number on those sorts of devices - but HOPEFULLY (am I being naive, here?) the use of sufficient warnings, and that coupling efficiency is nearly 0 if there "receiver" isn't tuned, will both serve to minimize this sort of problem.

Dunno, but the more I think about this, the more I'm convinced that any "charging station" that requires a cord will be a commercial flop unless it is delivers some compelling advantage (like 1C or higher charging current straight into the pack).


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## MJ Monterey (Aug 20, 2009)

Quick question on the paddle charger. 

Could the cable vandalism issue be resolved by flipping the connection? 

Put the paddle and cables on the car side and the "plug" on a short wall in front of the car.


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## dataman19 (Oct 7, 2009)

Boy, 
When you guys brainstorm - you brainstorm!!
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Woodsmith (post #2) - Yes it will take a lot of infrastructure. Most of the cost could have been paid by the NREL Grant for Infrastructure (that is until Congress amended the act to exclude non-utilities - Thank you Congress!!!).
Safety checks are a component of every viable commercial design (this is why space heaters are required to have tip-over switches).
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Pace makers will always be a problem. People with Pace makers are normally well aware of their hazards and risks (those with alheimer's and dimensia should be taken into consideration in every way - after all it should not be a goal of society to prey upon the weak). But ye there needs to be considerations about these issues.
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rankhornjp (post #3)- I think I addressed your points in my last post. Points well stated and I thank You...
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Dtaman19 (post #4) --- Oops - That's me (I guess I fall in the mindless thought category)...
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 dimitri (post #5) - Yes I am aware of the paddle charger methods. I am also aware of the potential problems. There are many cons and only a few pros - just like the plug-in chargers. As an example - We have had gasoline pumps since the 1950's - yet people often drive off with the hose still in their gasoline fill receptacle. You would think they would learn - but I guess you cannot possibly account for every dumb thing that the Human being does? Or can you?
.. As for the coils needing to be in close proximity - not quite so. For 99% transmission (or even power coupling efficiencies above 80% you would have to have a distance shorter than the square root of the Field Coil Flux Density - which is roughly 10 times the coil wire bundle diameter multiplied by about 1/2 the distance between the coils and multiplied by 3.14. So a loop with a loop diameter of 3 feet and a bundled wire coil with a diameter of the wire bundle of say 8" (a common size for air core transformers) you are looking at a distance in excess of 6 inches (easil;y adaptable). The coil flux density changes based upon frequency. Your inductive frequency is limited by the frequency interraction with other RF devices (ie radios, Computers, etc - even pace makers and hearing aides) and the ability to control 1st and particularly 2nd, 3rd, 4th and even 5th order harmonic radiation (these are the additional frequencies produced. For example, if you have a 100KHz transmitter, your ist level harmonics are 200KHz and your 2nd level harmonics are 300 KHz and 400 Khz, your third level harmonics are 300KHz, 600 KHz and 800 KHz - they get more complicated because they tend to interact and overlap from here on up - but they also decrease in intensity as the harmonics interact with each other and as the distance from the coil increases).
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 samborambo (Post #6) - Inductive chargers for people movers have been around since Uncle Walk used them in the original Disney Land. In fact Disney Corporations Imagenerring, Inc owns most of the intellectual property rights and patents for Indusctive Charging systems. How do I know this - Because I watched them build Disneyland. Even back then I was a handfull and too inquisitive for my elders - but Walt was ahead of his time, too bad his kids never adapted their dads traits...
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The low speed people mover is a controlled environment. They have a set nbattery size, a set charge rate, and a set environment. A public access charging port would not have these luxuries and would present many more challenges.
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 Woodsmith (Post #7) excellent point. And probably the best idea for implementation.
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But remeber- there are always trade offs. Just like carrying around the on-board 220V/110V Vharger in the EV - the additional mechanicals and electronics is additional weight, weight that detracts from the miles per charge. Still a decent approach..
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MJ Monterey (Post # 8) -Excellent Concerns. And extremely valid points. There will always be incompatible scenarios. Pace Makers are always concerns with any electromagnetic or Ionized Energy Systems. For the uneducated: Ionized Energy is the proper term for electromagnetic radiation or RF Energy. Since RF systems impart electromagnetic energy into the infinate impedance of free air the result us ionized energy. Just as sunlight is ionized energy, and is most charictarized by the phenomenon known as suns spots - which dump an inordinate amount of ionized energy that disrupts radio communications and even power transmission lines (and yes sometimes impair pace makers).
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You description of a buried electrical utility line causing problems with sanitary and potable water plumbing is a good example of collateral effects. It is also the reason that the National Building Code establishes new standards in separation distance and the use of sand barriers to negate these effects. Same rationale could be applied to this In Ground charger project. These additional seemingly non important factors should be considered and evaluated for possible implications.
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 Tesseract (post #9) I see the light bulb shining above your head.... Yes it would be great - when perfected. When that will happen, who knows. Most of the research is aimed at extending the 100 mile per charge range now attinable. There is no glory in designing a parking spot, most engineers see this as a minor endeavor, after all what good are they if the cars aren't in production. But then what good is producing the cars if you don't have a charging grid in place (ah the ole Chicken vs The Egg scenario...).
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Today, 03:57 PM MJ Monterey (post #10). Yes the vandalism issue is reduced significantly by placing the moving coil in the vehicle undercarriage. But as stated earlier - this increases vehicle weight. It also means the driver will need better parking skills. Putting the extender arm assembly in the road bed wiould allow for side to side and foreward backward adjustment (called X-Y-Z axis control).
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This is the only lengthly response I will give in this thread. I apologize for not responding in kind earlier. You have all contributed emmensely and I thank you.
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We believe the roadbed platform that elevates andadjusts side to side and forewards and backwards is the most practical. The only actual vandalism issues are when the platform is raised. Then the platform can be jammed with a brick or Iron bar. To minimize this problem the whole system must be designed to trap the vehicle and hold it in place (disconnect the ability to drive off) while the platform is trapped. This would allow for the opportinity for a technician to remove the obstacles prior to the vehicle moving and exposing the system to vandalism. But it also means there will be an extremely upset owner/operator of the affected vehicle. Ah - what to do...
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So you see - we haven't solved all the problems. But I believe we are at a significant start..
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dataman19
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## rankhornjp (Nov 26, 2007)

dataman19 said:


> ...If some idiot places two coat hanger wires across the terminals and then attaches them to his portable stereo, energizes the charger with the intent of powering his stereo while he Tailgates at the Mall, Stadium or whatever - Should he electrocute himself - the operator of the charger along with the owner and the Manufacturer could be held liable....


The chargers I've seen wont "start" until there is a "request" for power from a battery (i guess any load would work), so the contacts aren't HOT all the time.

Thinking out loud: 
retractable covers for the contacts that prevents access until a set of parameters is met.

some kind of weight switch so that the contacts are only exposed when there is a car parked on top (problem: could be over come by lots of people standing in the space, not very practical, but doable)....

RFID chip (or similar) mounted in the car to open the covers and turn on the charger, coupled with a "membership" contract that releases owner of liability in case of misuse? You would have to limit the range so that it couldn't turn on more than one parking space at a time, or network the chargers together to accomplish this: if RFID:1234 has activated charger 3 then it can't activate any other chargers. (Problem: someone stupid enough could crawl under the car and get power...)

let 3-4 fry themselves and maybe everyone else will learn? Probably the most expensive option....


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## dataman19 (Oct 7, 2009)

Good post..
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except "let them fry themselves"..
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That sounds like a true litigation lawyer in the making...
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But the concept would work out in the long run..
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dataman19


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## MJ Monterey (Aug 20, 2009)

Dataman, going back to your basic at grade concept. 

Would it be feasible to house the emitter in a full width (6 feet?) parking curb (raised area in front of the car about 2 feet deep) and have the cars receiver mounted between the front bumper and front tire? 

This would mount the emitter surface permanently 4 inches or so above grade.

Single axis automated adjustment side to side to allow for the parking challenged.

If they are too far vertically away it becomes the vehicle owners responsibility to drop the receiver (via a parallel link set up?) after handshaking protocols. Safety interlocks for the arm if needed are vehicle owners responsibility.

Jack


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## MJ Monterey (Aug 20, 2009)

As an update a friend forwarded this to me:

http://www.physorg.com/news199685767.html


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## GerhardRP (Nov 17, 2009)

MJ Monterey said:


> Dataman, going back to your basic at grade concept.
> 
> Would it be feasible to house the emitter in a full width (6 feet?) parking curb (raised area in front of the car about 2 feet deep) and have the cars receiver mounted between the front bumper and front tire?
> 
> ...


Jack and I are on the same wavelength. The charging station would be a head-in parking space. The reciever would be in the front bumper. Vertical alignment would be by specification. Horizontally, use Jack's scheme.
Gerhard


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