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Pics/Info: Inside the Tesla 100 kWh Battery Pack

Discussion in 'Model S: Battery & Charging' started by wk057, Jan 24, 2017.

  1. JRP3

    JRP3 Hyperactive Member

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    Actually some of the highest C rate chemistries, LiFePO4 and LiTi, have higher cycle life than NCA. However they have the worst specific energy while NCA has the best.
    Regarding cell size and C rate, usually a larger cell size of the same chemistry will have a lower C rate than a smaller size, so the 2170 cells should not be expected to have increased C rate from the size increase alone, if anything it would be slightly lower. Tesla may be doing other things to compensate for that.
     
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  2. LargeHamCollider

    LargeHamCollider Battery cells != scalable

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    Yep, battery cells != scalable.
     
  3. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    A lot of the limitations here are thermal based, including wires, bonds, and pack cooling. Redesigning the pack to have more cells in series instead of in parallel would lower the current and raise the voltage. This would improve the thermal issues during charging.

    Going to an 800 V system would let you charge at 240 kW with the same wires and cooling that we have now because the currents, and therefore the thermal properties, would be the same.

    The disadvantage of higher voltage designs then comes into the motors and inverter -- they will have to be designed for 800 V supply, and require higher voltage components, different windings in the motor, and more insulation.

    The other way you could do it it to split the battery pack into two 400 V packs. When driving, run the packs in parallel to get a 400 V system and use existing motors and inverters. When charging, connect the packs in series and charge at 800 V, or use dual charging connectors to charge each pack individually at 400 V.
     
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  4. JRP3

    JRP3 Hyperactive Member

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    Not the thermal issues inside the cells.
     
  5. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    True, you still have to cool the cells more. But at least the charge port, pins, supercharger cable, HV wiring, junction box, contactor, and other items wouldn't be affected thermally. They may need more insulation to deal with double the voltage, however.

    I think you could cool the cells adequately with higher coolant flow rates, or additionally with the heat pipe design that's been discussed.
     
  6. MP3Mike

    MP3Mike Well-Known Member

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    I highly doubt it since he carefully sealed the pack back up and then upgraded his Model X to a P100DL with it.
     
  7. JRP3

    JRP3 Hyperactive Member

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    There are still limits to how quickly heat can move from the inside to the outside of the cell no matter how quickly you can cool the outside. Also there may be more limits on charge rates besides heat related. Undesirable side reactions and thickening of the SEI layer may result from trying to move ions too quickly. A simple analogy would be trying to push gummy bears through a tennis racket. Take your time and you can do it without much problem, try to jam a handful through at once and you'll have gummy pieces sticking the the strings, further reducing the open space through which gummys can pass.
     
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  8. J1mbo

    J1mbo Active Member

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    Gummy bears and tennis racquets. @JRP3 wins the internet :)
     
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  9. NOLA_Mike

    NOLA_Mike Grouchy

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    Mmmmmm.... Gummy Bears....

    :)
     
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  10. scaesare

    scaesare Well-Known Member

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    Certainly true. Perhaps I should have made it clearer that when I wrote "I wouldn't discount this so easily" in my response to the other poster, I was referring to the need for a cell that had all those other parameters AND cycle life as well. It's striking the right balance.

    Thanks for pointing that out.
     
  11. Yggdrasill

    Yggdrasill Active Member

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    The 800V battery voltage is quite hyped. It started with the mission-e and then it's just gone from there.

    You don't need 800V for faster charging. With a liquid cooled supercharger cable and plug, more heavy duty cabling in the car, and a battery pack that is sufficiently cooled to accept the power, you can probably charge at 250 kW and 400V.

    Of course, if the cable harness for the 100D/P100D hasn't been upgraded from the charge port, we do know the current cars can't accept such power levels. However, the 100D/P100D is likely capable of accepting higher power than the 90D/P90D at a greater range of SOC. For example, if the 90D needs to ramp down to 20 kW at 90% to protect the batteries, the 100D should be capable of accepting around 23 kW. That is with equivalent cooling. The 100D seems to have at least a somewhat better cooling solution. The coolant channels have much more contact area with each cell, which means it should be possible to keep them cooler, and maybe 25-30 kW might be possible where a 90D/P90D might only charge at 20 kW. Some of this potential may only be unlocked with an upgraded supercharger.
     
  12. wdolson

    wdolson Well-Known Member

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    When supercharging at the current 120KW rate, each cell is getting 16.9W of energy. They could easily got to 140KW for the 100KWH pack and still have the same power to each cell.

    Considering how hard the car's cooling system has to work to keep temps under control while supercharging, they probably aren't going to be able to up the power all that more dramatically without a much larger cooling system, which adds weight to the car.

    In engineering most things are a trade off. You get a gain here, by losing something there. One example is the difference between the P version and the regular 90/100 version of the S and X. The range of the P version is less than the standard version because you need to lug around a larger back motor and some extra weight to gain what is really marginal performance for everyday driving. For the few people who want to drag race, it makes a difference, but not for the vast majority of people who only drive on the street.

    It's possible to make a car that supercharges say 25% faster than the cars currently do. To achieve that, they need to build more expensive superchargers with heavy duty cooling to deal with the extra heat, the cars needs a heavier duty cooling system to deal with the extra heat in the battery during charging, and somebody needs to pay for the wasted energy. That heat comes from energy that came out of the power lines, but didn't get stored in the battery.

    We have a lot of promises from companies that there will be super duper chargers on their cars, but at the moment it's just vaporware. There is only one company that has any experience fast charging electric cars with large batteries in the real world. I expect Tesla will tweak the superchargers to be a little faster, but until we have a better battery tech I don't think we'll see dramatically bigger power ratings on superchargers. As the power level goes up, you get into diminishing returns because your losses start going through the roof.

    Elon has said the real future for electric cars is supercapacitors. They have a lot of promise from a charging perspective. They can be charged dramatically faster than batteries and don't produce the heat batteries do either charging or discharging.

    However they don't have the charge density needed with what we have today. There was news a month or so back that the material used for contact lens shows promise as a much better dielectric than what has been used, but that tech is still in the laboratory. Even if it proves out in the lab, it will take many years before that tech can be in cars.

    When we have supercapacitors, cars can be charged as fast as putting fuel in an ICE, but it will require very high power charging stations.
     
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  13. TonyWilliams

    TonyWilliams Active Member

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    Wow, lots of great ideas flowing.

    Certainly, today, it would be somewhat easy to make current 120kW Superchargers supply the car through left / right ports at up to 240kW DC.. No fancy "800 volt" stuff. The problem, as stated above, is neither the battery nor the vehicle cooling system can withstand that for more than a very short amount of time (if at all). By the way, the Porsche 800 volt car is only talking about 220 kW of charging. Folks like to jump to the theoretical limits of the charger (like 350kW and 400kW that is being casually used) as anything meaningful for the car. The Tesla Supercharger has a limit of 135 to 145 kW, but the Supercharger output and car input is only 120 kW DC max.

    With the current charge module capable of 72 amps (72 * 277v = 20kW each), I suppose it would be possible to upgrade the current Supercharger box with 12 of these units for about 240 kW AC input, with about 200-215kW DC output capability (85-90% efficient).

    The cooling issue could be routed off-board the vehicle, with a large heat exchanger sitting at every Supercharger. This would require a cooling fluid coupling to the car, much like the coupling used for battery swapping.

    I think we all presume that the 2170 cell will charge faster, but I'm not as convinced. The larger the diameter of the cell, the harder it is to cool. In addition, we have no idea what chemistry is used, but it's safe to say that it won't be a radical departure from what they are using now... NCA. Tesla cannot afford to bet the farm on something radical, and they are way past experimenting with a Roadster.

    As to super capacitors, they could be energized with other super capacitors to recharge vehicles. The Tesla Uber Charger could be chugging along at 1MW to charge up the Uber station capacitor, which would then get plugged into a Class 8 semi truck, which downloads to an onboard vehicle capacitor at 3MW. Obviously, there would be some time before the Uber capacitor could do this little trick again (about once per hour).

    Using my example, a Class 8 truck with a 1MWh battery would charge in 20-30 minutes, and the load on the grid is 1MW. Currently, Superchargers already have a 500KVA transformer for 4 Superchargers / 8 stalls, so going to a single "pump" at 1MW isn't too crazy. Getting 5-10 Uber Chargers at one site would be an entirely different equation! Like the Gigafactory, it might take a lot of batteries nearby to be practical, particularly in rural areas.

    This is the minimum that will be required for a Tesla truck to be competitive. At least 300 mile / 500 km range under load. 2-4kWh per mile) with 20-30 minute refill times every 150 miles (like Superchargers). The offset in increased donwtime over a traditional diesel truck can be offset with decreased energy costs, but the savings can be surprisingly small to non-existent:

    $0.73 per mile @ 6.5mpg with $4.73/gal diesel (using $1.25 USD per liter in Europe equals $4.73 per US gallon)

    $0.46 per mile @ 6.5mpg with $3.00/gal diesel (that will likely go up in price over time)

    $0.38 per mile @ 8.0mpg with $3.00/gal diesel (latest Cummings X15 diesel motor at over 50% efficiency)

    $0.57 per mile @ 0.35mile/kWh with $0.20/kWh electricity (California electricity can easily be over 20 cents, plus demand fees will inflate costs further)

    $0.34 per mile @ 0.35mile/kWh with $0.12/kWh electricity (nationwide average US retail price, no demand fee)

    $0.17 per mile @ 0.35mile/kWh with $0.06/kWh electricity (wholesale, Pacific Northwest retail, no demand fee)

    My calculations for EV truck energy consumption are based one gallon of diesel #2 is 38kWh, so using 7mpg = 5.4kWh of diesel energy per mile. If we assume that is 45% efficient, and electricity is 85% efficient from the grid to the truck, plus truck consumption, then 2.86kWh of electricity is required per mile, or 0.35mile/kWh.

    If electric trucks catch on, expect a road tax surcharge like diesel trucks pay on fuel per gallon, which will further narrow any savings with EV trucks.
     
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  14. Matias

    Matias Active Member

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    Most efficient ice engines to my understanding have clearly less than 40% efficiency.
     
  15. Cloxxki

    Cloxxki Active Member

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    28kWh battery (perhaps a bit more measured like Tesla does), charging at 69.3kW.
    If 3 such packs fit in a car, with 3 plugs it would charge at well over 200kWh.
    Seems to be vastly superior battery technology in terms of charge speed (C).
    The little battery will not charge at 500km/h like a good Tesla, probably 350-400km/u or so. But a similarly long range car with this tech, would charge at well over 1000kph. Imagine charging 10x faster than driving consumes.
     
  16. brkaus

    brkaus Well-Known Member

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    I believe it has active cooling? In addition to the three charge ports, it would likely need 3x the cooling capacity.
     
  17. TonyWilliams

    TonyWilliams Active Member

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    The cooling on these LG Chem cells is real basic... a flat plate at the bottom with coolant flowing through. There is some "goop" to aid in the transfer of heat, but again, real simple.

    There are likely several issues at play. Possibly low impedance (which means less waste heat) and possibly more tolerant to heat.

    The 28kWh is net, as the pack in the Hyundai and Kia products are quoted that way (which is entirely different than Tesla).
     
  18. JRP3

    JRP3 Hyperactive Member

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    It's an LG Chem cell, right? So inferior in terms of specific energy.
     
  19. wdolson

    wdolson Well-Known Member

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    It boils down to battery supply. Right now nobody is capable of building enough EV delivery trucks to meet their needs. Tesla is likely going to be the first company able to meet that demand.
     
  20. Bangor Bob

    Bangor Bob Member

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    #120 Bangor Bob, Jan 31, 2017
    Last edited: Jan 31, 2017
    Existing trucks are already... Not completely terrible. At least the ones that try. There's only so much you can do, the frontal area is huge.

    A significant portion of the aero drag is due to the gap between the cab and the trailer. If Tesla can do something clever there, it would pay big dividends.

    [ edit ] Although.. This guy seems to have figured out how to double his highway mileage fairly inexpensively.
    An Aerodynamic Trailer Design More Than Doubles Fuel Economy
    [ /edit ]
     

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