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Brainstorming for an inexpensive automated charging solution

Discussion in 'Model S: Battery & Charging' started by Todd Burch, Aug 8, 2015.

  1. Todd Burch

    Todd Burch Electron Pilot

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    The metal charging snake prototype that Tesla recently demoed had me thinking some. While the snake is really cool, it looks mechanically complex and not at all inexpensive.

    So this had me thinking about some ways that future Tesla vehicles could support automatic charging.

    First, before the discussion goes off on wireless charging: It's simply nowhere near efficient enough, and probably won't be for another 10-15 years. So I was brainstorming a design for how vehicles could charge automatically, until the major disadvantages of wireless charging are eventually overcome.

    This is not intended to be a retrofit for a Model S--I understand that this requires a modification to Tesla's skateboard design, but I think it is doable with relatively little pain.

    Existing solutions involve the charging snake, or an articulated robot arm that plugs the existing connector into the car. While a robotic approach is certainly not too difficult to implement and could be decently reliable, it has a few disadvantages:

    1. Cost. Such a system is not likely to be easily affordable.

    2. Size constraints. A robotic system (snake or articulated robot) would require a certain amount of space next to the car to operate. Some charging situations may not have this space available.

    3. Complex. Because it involves moving parts and control systems, it is inherently less reliable than a design with less moving parts.

    So here's what I was thinking.

    First, an existing side-mounted charge port is necessary on cars going forward, because there is so much infrastructure that uses the traditional plug approach. The proposal below would be ideal for home use (a garage or parking space) or for Superchargers.

    It would work like this (excuse the horrible hasty Photoshop hacking, I am a mechanical engineer but lack artistic skills...especially when using a touchpad ;):

    On the underside of the car would be 5 flat, thin copper pads...maybe 6"x6". Each of these pads would be concealed behind a small sliding panel (could be plastic) on the bottom of the car to protect them from dirt and the elements. Each panel has a small lip at the front edge which you can grab and slide aft with your hand. When released it is closed by spring force.

    Each of these pads on the car would be connected to +120V, -120V, Neutral, Ground, and one for handshaking:
    pads.jpg

    On the garage floor would be 5 roller arms, each set up with a spring so that they naturally want to press up against the bottom of the car. The wheel itself is conductive and attached to, in this particular example, the +120V line:
    system.jpg

    As the car drives over these, the spring compresses to the proper height of the bottom of the car. As the roller approaches the lip on the sliding panel, it catches it and slides it back, exposing the copper charging pad. The spring force is enough to keep pressure on the lip to open it, and maintain good contact with the copper pad, but if the car keeps going the wheel will roll under the lip with no damage done.

    So anyway, the car stops with the wheel contacting the pad and communicates to this device that it is now in park. A handshake process begins, and the device begins ramping up current. The current flows through the wheel, to the pad, and into the car.

    This device could be screwed onto a garage floor, wires could be fed forward (so you don't drive over them), and there are probably several ways to "guide" the car so that the wheels are over the pad.

    The point was that this type of thing could be implemented fairly cheaply and installed in any garage or parking space easily. It has few moving parts, requires little additional hardware on the car, and the guidance to get lined up wouldn't be too difficult. (The copper pads could be increased in size to, for example, 1 ft x 1 ft if needed.

    Just initial brainstorming. Each wheel would need some sort of safety shroud, and weather considerations would need to be taken into consideration, but just wanted to through this initial brainstorming out there. I've gotta go for now :).
     
  2. vitaliy

    vitaliy Member

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    I was thinking about a tail-like-cable (ridgid) that will extend and fall. The lower end then would be moved slightly to left/right by ground supercharger...
    Sorry for my broken english, but it's like tailhook for aircraft cruisers Tailhook - Wikipedia, the free encyclopedia
     
  3. RDoc

    RDoc S85D

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    It seems to me that the first question in any design is "What are the use cases?". Personally, I don't see any compelling ones for home use and only some pretty esoteric ones for public use, but I'd strongly suggest that before designing something, come up with a set of requirements.
     
  4. mgboyes

    mgboyes Member

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    I'm sorry to be so blunt but your idea is terrible. Dangerously unsafe (exposed copper pads and wheels and whatnot with mains voltage on them, while charging is in progress), mechanically fragile (sprung connectors that might not catch on the underside of a flat-bottomed Model S but which will almost certainly get ripped off the first time someone drives an ICE over them, or fatally damaged when someone drives diagonally over them and they have to bear the weight of a 2.2 ton car), and likely to be highly inefficient and/or a fire hazard in real world conditions (what happens when the pads are dirty, or have some dry grass caught on them?).

    There are wireless charging systems in use today that are 90% efficient from supply to battery, which is not far behind wired connections. If Tesla wanted to fit a new charging system to their cars, that's what they'd do.

    As it is they need to deal with the nearly 100,000 cars that are already on the road, and I think the snake idea is a pretty solid bet. It wouldn't necessarily even need permanent installation - you could just put it on the floor at the side of your garage and let it do its thing (though obviously mine will be installed on the ceiling and hang down to connect to the car :)
     
  5. Canuck

    Canuck Active Member

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    I'm not all that inconvenienced by having to plug it in.
     
  6. deonb

    deonb Active Member

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    Me too. But this is not about that. It's about the car parking itself on auto and having to plug itself in while you're not present.
     
  7. Todd Burch

    Todd Burch Electron Pilot

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    Agree that it's not a big inconvenience, but:

    1. This would eliminate the possibility of "forgetting" to plug in. (It's never happened to me, but I know it happens to some).
    2. Cord gets out of the way when in a narrow garage (my case).
    3. It *is* one less thing to worry about.
    4. It's a "neato" thing that helps sell cars.
    5. It's another dagger in the heart of the ICE (you mean I don't even have to plug it in?), therefore it advances the market toward EVs.
    6. It enables self-parking and self-retrieval.
    7. It could reduce Supercharger congestion. Park by a Supercharger, and the car automatically pulls into a spot, charges, then moves back out of the spot while you eat lunch.

    There are probably other reasons I haven't listed.
     
  8. deonb

    deonb Active Member

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    Let's set a baseline.

    For an idea to be better than wireless charging, the delta in cost over wireless has to be less, or be more environmentally friendly than the 12% efficiency losses from wireless charging.

    So over 100'000 miles of charge, wireless charging losses will be 12% of 100'000miles at 350wh/m = 4200 kWh @ 12c = $504.

    That means:

    Your baseline for cost difference is: $504
    Your baseline for CO2 difference is: 5082 lbs (natural gas)


    Both would be a tough target to beat, but by all means - do try.
     
  9. Todd Burch

    Todd Burch Electron Pilot

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    deonb, last time I looked into it, wireless charging was actually quite a bit lower than the current efficiencies. I'm now reading about systems that can deliver 40 kW at 90% efficiency...that's actually really good, and I think justifies wireless charging.

    Wow, I'm impressed. That seems to change everything. Question is, what is the cost of an inductive system that delivers that kind of efficiency and is still capable of delivering 10kW or so of power?
     
  10. deonb

    deonb Active Member

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    I can't find any prices on that. However, fundamentally the amount of copper inside a 10kW induction charger is going to be around the same as the amount of copper inside a 10kW isolation transformer. So here's a 10kW isolation transformer for $2500
    http://www.cnet.com/products/apc-isolation-transformer-transformer-10-kw-10000-va/

    You have to separate this into 2 devices, which Plugless Power has already done at a cost of $1500. So add these together and you get a price of around $4000. That would be my guess at a ball park for a 10kW induction charger.


    I think for most uses the 3.3kW from Plugless Power is enough though, giving ~100 miles of range/night. That means your UMC stays in the car unless you returned from a long trip and are out of range, in which case you can take out the UMC and plug in. For the majority of time for the majority of people, the car will do fine with 3.3kW though.

    I think the Plugless Power problem isn't the 3.3kW, but fitting the charger underneath the Tesla battery, otherwise I'm sure they would have come out with something for us already.
     
  11. Todd Burch

    Todd Burch Electron Pilot

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    With efficiencies at 90%, it makes me wonder why Tesla hasn't started to integrate inductive charging as an option on their cars.
     
  12. PluglessSteve

    PluglessSteve Member

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    Heya, Steve Cummings here - full disclosure, I work for Plugless. A couple points to consider and a timeline. 1. moving parts and friction points mean wear and tear...this is not a problem with wireless EV charging (WEVC) 2. how about a 6.6kW Plugless system for Tesla that will be available in months? Stay tuned.
     
  13. Jason

    Jason Member

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    Such a tease!

    any details you can share?

     

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