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Battery pack spec speculation

Discussion in 'Model S' started by Palpatine, Mar 29, 2009.

  1. Palpatine

    Palpatine Banned

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    That is not too far off. I just bought a big pack of LiFFePO4 batteries from China for a RAV4 EV conversion that we are doing. 34 kwh is the size. 105 units of 100 Amp hour large format batteries.

    The total cost was $11,550 or about $1.10 per amp hour. I am positive that if we bought in a larger bulk order that it would drop in price another 20%.
    So realistically I could get that battery pack for around $9,000 if I was making a larger order.

    If a buyer is making a smaller order in the USA, it is about 50% more expensive than what I paid. But a larger company buying in the millions of dollars would pay less.

    That 2009 RAV4 will do about 100+ miles of range once it is converted. Highway capable at 90 mph top speed. Projected life of the batteries is 100,000 miles or 7 years.

    We are not that far away from $5,000 for a 100 mile range lithium battery pack. I think within two or three years we will be there.
     
  2. dpeilow

    dpeilow Moderator

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    I've been running some numbers on possible numbers/Ah combinations to see what range is possible and what will likely fit under the car. We heard that the smaller pack will be around 6000 cells and 42kWh, which means that 2000mAh cells would work for 160 miles if they are sticking to 18650s. (I'm assuming that the extra weight and parasitic loads when compared to the Roadster are already taken into account.)

    We also heard that the larger battery would be 'about 8000 cells' - well, ~8200 would allow 2600mAh to be used to reach 300 miles (someone please check my figures).

    Interesting, then, that we haven't even got into the realms of those 2900mAh and 3600mAh Panasonic cells yet.
     
  3. WarpedOne

    WarpedOne Supreme Premier

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    #3 WarpedOne, Mar 30, 2009
    Last edited: Mar 30, 2009
    Interesting, I was doing those calculations yesterday but then decided to scrap them as that post became quite unreadable. Yes, both 160 and 230 mile packs seem to use 2000mAh cells.

    But!

    This car has 300kW of power and around 80% efficiency, meaning PEM will draw around 370kW of power at peak. If we assume 370V as the pack's nominal voltage (100 cells in series) then the batteries have to be able of producing 1000A of current!

    With 370 V pack's nominal voltage there would be 55 cells in parallel in smaller pack and 78 cells in parallel in bigger pack. 1000 A from 55 parallel cells mean one cell would have to produce 18A. In the bigger pack where 78 cells are in parallel, one cell would have to produce 13 A. With 2000mAh cells those currents translate into 9C and 6,5C discharge rate which is a lot and doesn't bare good for cell life.

    Yes, 370kW is peak power and won't be sustained, but even 10% of that i.e. 37kW which will be required for sustained highway travel would suck 0,9C and 0,65C from cells.

    I don't know what kind of cells would last 7 years under regular 0,9C or 0,65C discharge rates (last = not loosing more than 20% of nominal capacity). That's why I suspect Tesla will use higher capacity cells but won't use their whole capacity so they will last longer.

    If they use 2500mAh cells, those 0,9C and 0.65C discharge rates fall down to 0,7C and 0,5C. With 3000mAh cells those rates fall again down to 0.6C and 0.4C. Such rates are much easier on cells and won't degrade them so fast.
     
  4. TEG

    TEG TMC Moderator

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    #4 TEG, Mar 30, 2009
    Last edited: Mar 30, 2009


    Yeah, I had already done that. I had seen the 6000 & 8000 numbered published but also saw these:

    • 160 mile range base pack (42kWh, 5500 cells)
    • 230 mile range upgrade (~60kWh 7800 cells)
    and went with those numbers, and put them in the specs here.

    I also saw this quote:
    "They use the same battery tray for all three options... The 160 mile version will not use all the room in the tray, the 230 mile version would be full and the 300 mile version would be using a different type of LiIon battery with more energy capacity."

    Here is where I wrote:
    So, assuming 5500 for 42kWh and 7800 for 230 & 300, then the math is close for 2200mah, 2200mah and 2600mah respectively.
     
  5. WarpedOne

    WarpedOne Supreme Premier

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    None of these. It would only add cost and conversion losses, but wouldn't really solve anything. The key is in finding the optimum in cell's capacity, energy and power density and cost (= annual manufacturing rates) and then not use whole capacity but only about 80%. Much easier said than done :)
     
  6. dpeilow

    dpeilow Moderator

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    All of which points to interesting times if a money-no-object, higher capacity version could be built. :smile:
     
  7. TEG

    TEG TMC Moderator

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    Yeah, I have wondered how they could put such loads on the cells and still have them last. Tesla may know more about what these cells can (and cannot) take than anyone at this point.
     
  8. EVnut

    EVnut Darell, the EVnut

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    Wow. Thanks for sharing that bit of info. I'll just shup up and listen now. (Of course the claim here is 160 miles of range on a $5,000 pack, but still).
     
  9. Kevin Harney

    Kevin Harney Active Member

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    My guess is that he was talking about a replacement pack down the road being that cost. Or perhaps by the time it goes to production 3 years from now being about that cost. And they usually try to make it sound a little better than it really is on top of that. My deal is I don't care !!!! All I care about is the cost in 10-15 years when I need to replace mine. Otherwise it is built into the car price.
     
  10. mt2

    mt2 Member

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    Tried to find the original post, but didn't look too hard. Wasn't that $5000 for an upgrade? In which case you may be getting some credit for the old pack, and Tesla might elect to eat some of the cost to get older technology off the road.
     

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