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Does the Model S battery use active balancing?

Discussion in 'Tesla Motors' started by Kwillscherer1026, Jun 28, 2013.

  1. Kwillscherer1026

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  2. Doug_G

    Doug_G Lead Moderator

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    This would cost $14,000 to $21,000 for a Tesla battery. Non-starter. Maybe for prismatic cells...
     
  3. CroDriver

    CroDriver Member

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    No - a BMS treats a string of any number of paralleled cells as one cell. The Roadster has 99 cells in series which means that the BMS monitors 99 individual voltages, no matter how many cells are in parallel.
     
  4. ggr

    ggr Roadster R80 537, SigS P85 29

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    I don't think this applies to the Model S battery and I'm quite sure it doesn't apply to the Roadster. Talking here about the Roadster: First, it depends on just which way the cells are all connected; is there one chain with 99 sets of cells in parallel, or is there some number of chains (each with 99 cells) wired in parallel? (I don't know, but I imagine there are people who do.) But even then, there are a number of independent sheets in the battery, and they would certainly each need their own balancers.
     
  5. Doug_G

    Doug_G Lead Moderator

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    Did you look at the article? It's showing an architecture that requires connections to every cell.
     
  6. drees

    drees Active Member

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    I'm fairly certain that the Tesla must be able to shunt/bleed off current from any single cell - can anyone verify? Or are they only able to balance "sheets"? If the latter - I wonder how they are able to keep cells in a sheet from going out of balance - 99 cells is a lot of cells in series and eventually even the slightest difference in cell characteristics will result in individual cells going out of balance...
     
  7. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    We know that each cell is individually fused. My thought, from what I've read, is that they can't turn off a single cell but they can turn off a small group of cells (way less than a sheet).
     
  8. strider

    strider Active Member

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    #8 strider, Jul 1, 2013
    Last edited: Jul 2, 2013
    I'm no battery engineer but from what I've read on the Roadster, they balance to the "brick" level, each of which has 69 18650 cells. 9 of these bricks are rolled up into a "sheet", of which there are 11.
     
  9. drees

    drees Active Member

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    Thanks, that makes perfect sense!

    In this configuration each "brick" has 69 cells wired in parallel. Voltage range of each brick ~3.0-4.1V.
    9 bricks are then wired into series to form a sheet. Voltage range each sheet is ~27.0-36.9V.
    11 sheets are then wired into series to form a pack. Voltage range each pack is ~297-406V.

    The 85 kWh Model S probably has more cells in each brick. The 60 kWh Model S appears to have a lower voltage by looking at 60 kWh pack SuperCharger voltage reports - I'd bet they use fewer sheets than the 85 kWh Model S.
     

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