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Tesla Roadster batteries

Discussion in 'Roadster: Technical' started by TEG, Jun 24, 2007.

  1. TEG

    TEG TMC Moderator

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    Since the site owner created this new battery section we might as well start it off with the known specs of the Roadster pack.

    Much info from here
    And here

    Tesla calls their battery pack the Energy Storage System (ESS)
    Tesla puts 6831 Li-Ion laptop batteries in the ESS.
    The batteries are a standard 18650 format
    The whitepaper says the pack stores 56kWh of energy when fully charged.
    It runs at a nominal voltage of 375volts (about 410v when full, 300v when "empty")
    Taking into account the voltage, the pack has a capacity of 152Ah.
    Expected pack cycle life: > 500 recharges.
    ESS total weight: ~900lbs.

    The above are the published facts. The following discusses some related details that are a little more fuzzy:

    The pack can be charged with a 240v, 70amp circuit in 3.5 hours.
    That is 16.8kW for 3.5hours or 58.8kW. There is some charger power loss, so it makes some sense to take 58.8kW to charge the 56kW pack.

    Here it says that the ESS has 11 "sheets" with 621 cells per sheet. There is apparently a separate CPU for each sheet to manage the energy being stored in each sheet. For some reason, many have mentioned that the pack is actually organized into 69 parallel groups of 99 serialized cells. This would make some sense as Tesla has said the cells max voltage is 4.15v per cell which x99 cells=410v which is the max voltage they say the pack gives to their PEM. They also shut down the car if the per cell voltage gets down to 3.00v which is the 297v minimum ESS voltage that has been discussed.

    There has been much speculation as to the exact brand and type of individual cells they use.
    Here they says that each cell is 2.2Ah.
    So, if you take 6831 cells * 3.75v (nominal) * 2.2mAh you get 56.355kWh which seems fairly close to the published pack capacity.

    It has been stated that the ESS can output about 600amps at 375 volts which gives 225kW

    For a 56kWh pack to output 225kW of power, the cells need to be able to achieve "4C" discharge.

    There are lots of 2.2mAh 18650 cells, but many can't handle 4C discharge rates safely or without damaging the cells.
    Some have said that a battery like the BiPower LR18650 or Tenergy might work in this application, although 4C discharge is pushing it hard past rated specs. (Perhaps Tesla only dips into the 4C discharge rate for short burst of acceleration then backs off to avoid overtaxing the cells?)
    Tesla may be using slightly more unusual "high power" cells that can handle the higher discharge rates.
    Quote from an article:
    "The primary reason that Li-ion rechargeable batteries aren't used in power tools is the electrode material used. Currently anodes use LiCoO2, which increases the energy density to provide longer battery drive times for digital gear. LiCoO2, however, has problems assuring safety because of the high heat generated when drawing high current, and as a result Li-ion rechargeable batteries never found much of a market in power tools.
    A change in the anode material, however, has allowed Sony to productize Li-ion rechargeable batteries capable of handling high currents. The firm will begin shipping its V and VT series of high-output batteries from January 2005. Safety at elevated temperatures was improved by switching the anode from LiCoO2 to Li(Ni-Mn)O2, with Ni and Mn content.
    Internal impedance, which presents a problem when drawing high currents, was also reduced to about 50mW (about 40% below prior designs) by adopting thinner electrodes and other measures. The new 26650VT battery, for example, measures 26mm in diameter and 65mm in length, and can continuously output 50A in 20C discharge (discharge in 1/20 hour). It can also output 70A pulse (see Fig). The battery capacity is 2500mAh, and the volumetric energy density 250 Wh/l."


    Here they say that max motor power is 185kW with 80% efficiency when making max power.

    To me, 80% efficiency means to me that the ESS needs to provide at least 230kW (because 80% of 230 is 185)

    The battery whitepaper says the ESS can output 200kW max. That seems a bit low.
    How can the ESS output "only" 200kW and still get 185kW from the "80% efficient at peak power" motor?
    Perhaps the eMotor is more efficient? Here they say it varies between 85 and 95% efficiency...

    Even though their battery whitepaper still says "August 16, 2006", I see that they have updated it since then.
    For instance, it talks about "more than 200 mile" range now, but originally it said "250 miles on the EPA highway cycle".
     
  2. AGR

    AGR Member

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    Its great to have information regarding the battery pack, and some of the science that is involved to develop a battery pack / electric motor combination.

    Does a customer care about the molecular make up of the gas in the tank of his car, or where it comes from, or who refined it, or in which pipeline it travelled. Gasoline is a commodity, and a battery pack is a commodity.

    The customer is going to care about one thing - it better do what its supposed to do, do it well, do it for a long time, and if it goes boing the customer will have no desire to pay for it. The fashion in which these battery packs are packaged it will be identified as just another "black box" in a car, a very expensive black box .

    At 240V and 70 amps to charge the battery, when the usual breaker in house is 15 amps - a stove uses 30 amps - the way homes are built these days in most breaker boxes there is no room to add 70 amps worth of breakers.  If I understand this correctly on a 110v 15 amp outlet (the normal outlet in a house) it would take 16 hours to charge the battery pack. Will the battery pack require a constant temperature while its charging?

    What makes sense is that most of the time the battery pack / electric motor combination is working at 50% of its rated capacities on the high side, since lithium batteries don't have a memory, use the car and top up the batteries (like going to the gas station after every use).

    Hopefully there is a self diagnostic system in the car that monitors the charge - condition(of each sheet) - performance of the battery pack.
     
  3. iisjsmith

    iisjsmith Member

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    The ESS is not a single large pack arranged in a 99S69P configuration.

    SRB posted this link (www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=14108) on the Tesla Motors blog. It has all the specs, and I've been able to work out some numbers.

    Each cell is 3.6V and 2200mAh. The cells are arranged into sheets, with each sheet being 621 cells. Each sheet is 32.4V, so if each cell is 3.6V then 32.4/3.6 = 9 cells in series. If there are 9 cells in series that means 621/9 = 69 parallel strings. So the wiring of each sheet is 9S69P. If there are 69 strings then 2.2Ah * 69 = 151.8Ah. So each sheet is 32.5V and 151.8Ah.

    There are 11 sheets, but one sheet is used just for the car's internal systems and is not connected to the motor. So you have 10 sheets used to power the motor. It says "The remaining 10 sheets provide 324 V for the motor" so that means the 10 sheets are connected in series. That gives us a final amount of 324V and 151.8Ah of energy to the motor. This works out to 324V * 151.8Ah = 49183Wh or 49.2kWh. Just where Tesla Motors says we should be at ~50kWh.
     
  4. TEG

    TEG TMC Moderator

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    iisjsmith,

    I read what you wrote, but I think it might be wrong.

    Yes, I saw the elecdesign.com article, but the "one big pack" idea seems to line up with other numbers I have seen elsewhere.

    This key article:
    http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf
    says:
    "The pack operates at a nominal 375 volts, stores about 56 kilowatt hours (kwh) of electric energy..."

    Your calculations produced 324 volts, 49.2kWh which are both much lower than what Tesla quotes.
     
  5. malcolm

    malcolm Active Member

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    #5 malcolm, Jul 29, 2008
    Last edited: Jul 29, 2008
    When will we see a 300 miles per charge upgrade?

    http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf

    This document was updated in December 2007 with the ESS dropping from the previously stated 56kWh figure to "about 53kWh" suggesting that the present ESS design is made up from 2.1Ah cells rather than 2.2Ah.

    Hopefully Tesla have a team of people looking at Li-ion durability but when can we expect to see a major revision in the Roadster specs? Roadster 2.0, if you will.

    For example, swapping the present 2.1Ah cells for 2.9Ah would (theoretically) increase the range from 220 miles to 303. This is likely to involve tweaking the PEM software, so my guess is that this will only be made available at the 100,000 mile service point were existing owners can decide whether to trade their existing ESS in for another 53kWh system, or pay extra for the 75kWh pack (6831 cells x 3.75V (nominal) x 2.9Ah).

    Cost and durability are the real deciders on when an ESS upgrade becomes available, of course. And since "99% of travel is under 200 miles per day" there is also the issue of demand. Roadster owners will be well versed in range optimistation. I know we all speculate that "more miles=always worth the money", but will they? Plus there is no reason why Whitestar technology development cannot enhance the existing Roadster package even more. More efficient cooling - for car and occupants? There maybe an entire range of desirable upgrade options available by then. (I'm sure many Wish List items will be posted on this site).

    For example, comfier seats may have to come before more miles :wink:

    However, getting back to the ESS, this is where Tesla's 50%, 90% or 100% recharge options fall down, since recharging to these same levels will always take 42% longer over previous times with a 75kWh pack (assuming owners continue with their preferred charging habits).

    I think the PEM and VDS software-side of this upgrade would need to include additional "Recharge to X kWh" options alongside the existing "Recharge to Y%". (Service Centre downloads of recharging methods and mileage profiles can inform all of this) And maybe the VDS could also show typical equivalent ranges for particular kWh values?
     
  6. vfx

    vfx Well-Known Member

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    Someone please check my math

    Batteries only get better with time. (new batteries that is)

    When Tesla appeared on the scene in 2006 it was said that battery technology was increasing by 8 percent per year. Is Tesla using those batteries from 2006 or the people who are getting cars in 2009 getting a car that gets 283 miles per charge instead of 225 miles?

    Another thought is if you buy a car with today's battery tech "now" and assume that nothing changes in battery science but the yearly 8 percent increase, does that mean in five years when you replace your battery pack that the 225 EPA mileage will increase to 355miles?


    Should this thread move to tech?
     
  7. malcolm

    malcolm Active Member

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    Er.....isn't it in tech? Or do you mean a more Battery-specific one? Dunno, it's been here for over a year.
     
  8. vfx

    vfx Well-Known Member

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    Yeah... The Electric Performance Forum section has "Technical" with a Sub forum called "Battery Discussion" That's where I think to go for this kind of discussion on batteries.
    But so far this thread has stayed specific to Tesla soooo, I guess it's correct here.:mad:
     
  9. dpeilow

    dpeilow Moderator

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    There is a 3100mAh Samsung "LVO" 18650 cell prototyping now which would give 317 miles in the Roadster.

    Also the 350Wh/kg Sion Power Li-S cells mentioned recently would give 463 miles by my crude calculations.

    So I think it is a fair bet we could see improvements for the next battery.
     
  10. malcolm

    malcolm Active Member

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    I think some of these higher capacity 18650 cells like the 3.1Ah's from Samsung and certainly the 3.6's from Panasonic achieve this by increasing the depth of discharge from 4.2V-3V to 4.2V-2V. This would require a major upgrade to the PEM. Tricky electronics, according to Martin, but not impossible. Usual suspects: cost-effectiveness and reliability.
     
  11. dpeilow

    dpeilow Moderator

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  12. DRM

    DRM Roadster #619

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    7 year Tesla battery life?

    Hi all, I finally made the decision to join this forum after over a year of lurking. There was one line in Elon's recent email that really grabbed my attention, and it didn't seem to attract much discussion in the owners forum.

    From Elon's recent email (bold added):

    "One of the top questions that we are asked about the Roadster, and indeed is asked of any electric car is, “How long will the battery last and what will it cost to replace?” Our calculations and test data indicate that a Tesla battery should last approximately seven years, depending on driving and storage conditions. The cost to replace a Roadster battery pack today is approximately $30,000, although it will certainly decrease with time (adjusted for inflation) as Tesla and our cell suppliers continue to find innovative ways to reduce cost. "

    I was always under the impression that the battery life was closer to 3 years ... not seven. Does anyone have any thoughts or know anyting additional w/r/t the battery lifespan?

    Thanks,
    Dan.
     
  13. Palpatine

    Palpatine Banned

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    Most of the quotes that I have read refer to 5 years or 100,000 miles. Since nobody is likely to drive a Roadster 20,000 miles per year, I felt that the simple aging of the batteries was the likely limit.

    So if Tesla believes they have enough data to support an estimate of 7 years of life, that is a positive improvement. I still don't think I will drive 14,000 miles per year in a Roadster.

    That having been said, I will not be buying the battery replacement plan for $12,000. It is a big leap of faith to say that Tesla Motors will be around 7 years from now. That is too far out and the market is too iffy.

    We can only hope that a replacement battery can be designed aftermarket.
     
  14. vfx

    vfx Well-Known Member

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    Or from whomever buys the parts. Like that guy in Texas who bought all the stock of DeLorean. He is the defacto dealer and has enough supply to build a "new" car if you like.
     
  15. TEG

    TEG TMC Moderator

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    Don't know how accurate, but here is some info we got in 2006:
    SiliconBeat: The Tesla Roader taken for a spin; and its "gut-wrenching" VC roadshow
    They have changed some things between 2006 and 2008, so it might not be the exact same pack now. Also, they probably learned a bit more in the interim.
     
  16. dpeilow

    dpeilow Moderator

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    I wonder how easy it would be disassemble the battery/ESS and replace the cells? Not to say that something else won't fail, but that seems the most likely item to replace.
     
  17. TEG

    TEG TMC Moderator

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    My guess is that full ESS/pack disassembly and individual cell replacement would be a royal pain in the you know what.

    My guess is that replace rather than repair is the plan when the time comes.
     
  18. Joseph

    Joseph Member

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    Yeah, from the sounds of their recycling plans, it seems they're definitely planning on complete replacement.
     
  19. vfx

    vfx Well-Known Member

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    #19 vfx, Feb 22, 2011
    Last edited: Feb 22, 2011

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