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Tesla cell-level fuse bondwire material?

Discussion in 'Technical' started by ASK1, Apr 14, 2015.

  1. ASK1

    ASK1 New Member

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    As you may know, Tesla uses wirebonding to connect each cell to the rest of the pack, and that these bondwires also act as fuses to remove the cell from the pack if there is a current surge involving that cell. Does anyone know what material they use for these wires? It is silver?
     
  2. obrien28

    obrien28 Midnight Engineer

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    Most likely silver/copper or some alloy thereof, you can read more about fuse materials in general on this Quora Page
     
  3. spaceballs

    spaceballs Member

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    No idea of the material, but I have a few used bondwires (from a Tesla Roadster ESS) if you like a few.
     
  4. ASK1

    ASK1 New Member

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    I would absolutely be interested.

    The reason I ask is that I'm making a battery pack for an electric bike, and I want to incorporate cell-level fusing into my pack. Most people building packs don't attempt to have cell-level fusing, so it's hard to find resources on the topic.

    I did find a paper that kind of covers the transient-heating math that's behind the fuse design. http://www.jpier.org/PIERM/pierm31/15.13051311.pdf
     
  5. spaceballs

    spaceballs Member

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    Sure PM me your address, note these fuses are pretty short so might be hard to re-use. I would only use them for testing.
     
  6. okashira

    okashira Member

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    They are aluminum
     
  7. kennybobby

    kennybobby Member

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    #7 kennybobby, Apr 22, 2015
    Last edited: Apr 23, 2015
    Thanks for letting us know. Have you measured the wire diameter?

    i'm going to guess for aluminum that it is #23 gage wire with a diameter of 0.0226" (0.574mm).
     
  8. okashira

    okashira Member

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    Not even close. :) 0.28mm is what I measure on both my p85 packs wires.
     
  9. spaceballs

    spaceballs Member

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    Confirmed the one bond wire from okashira (from a cells I got still had one on) it ranges from 0.27mm - 0.29mm.
     
  10. kennybobby

    kennybobby Member

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    That would be #29 AWG with diameter of 0.011", with a fusing current greater than 7 but less than 10 amps.

    That is quite puzzling with respect to the whiz kid jason's data, that the bond wires will pass 25 amps but fuse at 26--How can that be?

    The fusing current of 29 gage copper is greater than 10 but less than 14, but even that doesn't seem like it would have enough margin if the load were drawing 3 to 5 times the C rating of the cells. The 25 amps seems like the right amount of margin for the cells.

    Is there another material that can carry 25 amps (and fuse at 26) in the #29 gage diameter?
     
  11. okashira

    okashira Member

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    #11 okashira, Apr 27, 2015
    Last edited: Apr 27, 2015
    I don't think they are #awg anything, they are just custom solid aluminum wire, made especially for fuse bonding applications.
    Second, Aluminum, IIRC, is the highest fusing current material available per diameter due to high conductivity and thermal conductivity.
    Third, the fusing current is higher then you quoted, because they are only ~8mm long
    Finally, I don't know if it's 25A, but certainty more then 10A. If I get the time, I will test it.

    http://heraeus-contactmaterials.com/media/webmedia_local/media/downloads/documentsbw/brochure/HERAEUS_BondingWire_Brochure_2012.pdf
    Edit: looks like copper and gold are higher... but based on my estimation , 15-20 A for these alum wires.
     
  12. Natechal

    Natechal Member

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    This is a very helpful tip, especially for newbies like me.
     
  13. spaceballs

    spaceballs Member

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    Got your PM.
    I couldn't find my Roadster bondwires I misplaced them somewhere, but got bondwires from a model s pack (from okashira) and I just dropped them off in the mail.
     

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