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Redundant flex circuit

Discussion in 'Technical' started by Cosmacelf, Aug 2, 2017.

  1. Cosmacelf

    Cosmacelf Active Member

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    In today's 2Q conference call, Elon mentioned they were going to try to use new technology to reduce the wiring harness length to 100 meters in the upcoming Model Y (and Model 3 eventually too). He called this technology a "redundant flex circuit". Anyone know what he is talking about?
     
  2. SMAlset

    SMAlset Member

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    I posted this link in another thread on the Model 3 regarding concerns of things like lack of a heated steering wheel. Thought maybe it could be a clue as to why that feature wasn't apparently being offered (yet), and needless to say much to the chagrin of cold weather area drivers too. To me it made some sense. If they aren't ready to use the technology yet but it's been long in the works and near ready, why set up their production lines for a more traditional wiring option package like Cold Weather when a new way of supplying it will be coming down the road in the near term. Here's the article I saw.

    Tesla’s "flexible circuit" technology could spark wiring changes in EVs
     
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  3. BioSehnsucht

    BioSehnsucht Member

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    My take on it was that it might be something like USB-C (w/ Power Delivery) or Ethernet (w/ Power-over-Ethernet) where you have data and power signals together, with a "standardized" (as in, many identical connectors, not that there's some open standard) plug, and use switches / hubs to connect everything.

    Most likely would have 48V power, ground, and both a high speed CAN bus and ethernet signaling (though you could probably get by with just one or the other, CAN bus would be limiting for a few applications and ethernet overkill for most), possibly low speed CAN too. Certain wire harness segments might omit one or the other (i.e., your window switches might be power, ground, and CAN bus only). Each 'last mile' segment (a segment that terminates in something like a switch or gizmo, not another hub/switch) would just go to the nearest hub/switch, rather than having dozens or hundreds of wires running back to a common location. A hub-and-spoke or star topology rather than a home run one...

    And then you have a second, logically identical, but physically redundant set of connections. Possibly with the non-terminal connections being arranged in a ring (or two rings) so that no single point of failure (except on a terminal run) could interrupt data.
     
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  4. Cosmacelf

    Cosmacelf Active Member

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    That ... makes sense.
     
  5. Doug_G

    Doug_G Lead Moderator

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    Agreed, that makes sense.

    There's nothing new about flex circuits per se; small flex circuits are widely used throughout industry (heck we use them). But using them to replace wiring in a car is something I haven't seen before. You would think they would be more expensive than simple wiring; but thinking about it there would be a number of advantages and I can see how it could lower costs overall.

    As Bio pointed out, higher voltage DC allows you to use lighter wiring to deliver the same power. That makes using lighter weight flex circuits more practical.

    As for communications buses, those are already used in cars but flex circuits could make them better. Flex circuits can have tightly controlled impedance, which could help make high speed bus communication faster and more reliable.

    Another point is that assembling wiring harnesses is still a fairly manual activity. Flex circuits are typically assembled by machine. The only difference is that these flex units would be much larger than usual, so perhaps some new handling systems would be required. If you can eliminate manual assembly of wiring harnesses there is a big potential there to lower costs.

    Flex circuits can also have more on board than just connectors. They can also have electronic circuits built in. There could be communications switches and line drivers built right into them.

    CAN bus already helps reduce wiring in cars. Back in the day if you wanted a switch to operate a window, there had to be a wire from that switch to the motor. Now there are multiple signals traveling on a single wire. This technique would presumably expand on that.
     
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