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Power density Vs Energy density Vs Cost Vs Weight!!!!

Discussion in 'Electric Vehicles' started by carthikv12, Jul 31, 2009.

  1. carthikv12

    carthikv12 Member

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    What characteristics would mainstream cars need?

    A high power density?

    or a high energy density?

    and what value of power or energy density is required for say a 200 mile range with a 25KW motor? and what what will the cost of batteries be in a vehicle that weighs about 500 kg without the batteries and motor?

    and how does enhancing a battery for energy or power density effect cycle life?


    Thanks!
    Carthik
     
  2. TEG

    TEG TMC Moderator

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    Lower price, higher cycle life.

    It seems sufficient acceleration is already available.
    Better energy density (for longer range) is desired.

    Why 25kW? That is weak for a highway capable EV. As has been pointed out, higher powered electric motors don't hurt efficiency. It isn't like with gasoline vehicles where big engines hurt efficiency.
    Battery costs vary based on chemistry, pack size, etc. Basically to get a useful range, the ~$10K+ pack cost is still a barrier to mainstream adoption. Hopefully that changes soon. Were you wanting more specific information?
     
  3. carthikv12

    carthikv12 Member

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    Hi, first of all thank you so much for posting!

    I found that the mini E does a pretty balanced job - I found this on another thread here...

    572-pound lithium ion battery
    150 miles range per 8-hour charge
    Consumption 4.4 miles/kWh
    204-hp & 162 lb-ft of torque
    0-60 bit over 8 seconds
    Top speed limited to 95mph
    A bit over 3,200 pounds
    Regenerative braking
    More details:
    Lithium pack maximum capacity 35kWh.
    Nominal 380 Volts to motor.
    Contains 5,088 cells grouped into 48 modules - (approximately how much would this set up cost?) i'm looking to use exactly half this battery capacity... would that give me the same range in a car that weighs half the weight?

    In my design, i was planning on using two 25 kilowatt motors ... cos it's going to be a light car. around 800kg... with the batteries and motor. This is a car for 2020.

    I was thinking about twin motors because of better traction - but will using 1 50 to 60 KW motor offer a considerably more compact package? Where can i find information regarding dimensions of components? and also the state of li-ion battery tech in 2020? how much cheaper will they be and what will the power and energy densities be like then?

    Thanks!
    Carthik
     
  4. TEG

    TEG TMC Moderator

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  5. carthikv12

    carthikv12 Member

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    Thanks! I've posted there... but just in case, how does battery capacity calculation work?

    For example , this mini has a 35 kWh battery and a 150 kW motor.... It says 380 volts to motor. So this would be constant right? meaning at 150 kW, current drawn = 395 amps!!!!? but at 50 kW more like 130 amps? how long would the battery last at a constant power draw of 50kW?
     
  6. doug

    doug Administrator / Head Moderator

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    150 kW is the peak power of the motor, say under hard acceleration, not the continuous power needed to maintain a normal driving speed. It's like saying you have a 200 hp engine... it's not typically asked to deliver that power continuously.

    To first order: (35 kWh) / (50 kW) = 0.7 hours
     
  7. carthikv12

    carthikv12 Member

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    Hi Doug,

    Yea I understand the motor won't be on full throttle the whole time... but if its operating at 50 kW that battery will get drained in .7 hours?! How on earth will the mini ever get to 150 miles in that time! lol... are they being a little too optimistic?
     
  8. stopcrazypp

    stopcrazypp Well-Known Member

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    The MINI-E's range has been revised to 100 miles (it only uses about 28kWh out of the 35kWh and also the real world efficiency is lower than ideal estimates). In any car, if you use max power you will burn through your energy very quickly. For example the Veyron at max speed burns through it's fuel in ~15 minutes.

     
  9. carthikv12

    carthikv12 Member

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    Yea, so battery tech for cars will not work if we bring highway travel in to the picture right? It just seems impossible then! Unless there are some incredible breakthroughs in battery tech, though experts state that the energy density will struggle to exceed 200 wh/kg. And then theres the matter of cost which is even more frightening as a report states that the price has been stagnant for about 9 years... so the next 10 years won't make any radical changes?
     
  10. dpeilow

    dpeilow Moderator

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    Perhaps you should check some other threads on this site - such as the drive from Seattle down to Portland and those which talk about battery tech - before making sweeping statements like that.

    You've also made the assumption that 50kW is needed to sustain constant highway speed (it isn't).

    Also take a look at the blog post on the Tesla site from JB Straubel.

    [​IMG]
     
  11. carthikv12

    carthikv12 Member

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    I'm sorry I wrote that late in the night! guess i was frustrated about conflicting information! my bad though i apologize! but thanks a lot for ur post dpeilow... thats precisely the kind of information i've been hunting for! feel like i've stumbled across el dorado! lol... it's great to see promise for battery tech as i have reservations about fuel cell technology.

    But in your experience, have you come across any information about the potential cost of such batteries in the future? I'm looking at the state of the art beyond 2020... and I'm trying to understand the performance and weight of these batteries as well as the cost. If you could point me to any resources, i would be gratful!
     
  12. qwk

    qwk Model S P2681

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    Nobody knows for certain about future battery capabilities. If you look at computer technology and cost in the 1980's vs. now, it gives you an idea what is possible if electic vehicles are adopted as the replacement for ICE cars.
     
  13. vfx

    vfx Well-Known Member

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    Predicting tech that far out is a fool's game. When did you first get an email account?
     
  14. doug

    doug Administrator / Head Moderator

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    Tell that to Ray Kurzweil.
     
  15. vfx

    vfx Well-Known Member

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    OK, Ask him!
     
  16. carthikv12

    carthikv12 Member

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    lol guys... yea i know its not the ideal solution but what if u had to take an educated guess? because this is for a project... and i have to chose the technology that i think will be in use then. It's ok to be optimistic because its only an educational purpose, but i was just really curious to see if you guys had a reasonable idea based on the potential for cost reduction or something...
     
  17. dpeilow

    dpeilow Moderator

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    Well, Tesla are offering owners the option of signing up for a replacement battery in 7 years at $12k. That's probably under half what it costs them today.

    There have been various projections of the fall of battery cost, the figure quoted around here is 8% per annum. However here one of the commenters says that over the past 15 years it has been 17% per annum for li-ion.

    You may find this interesting: The Tesla Battery Pack Challenge
     
  18. JRP3

    JRP3 Hyperactive Member

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    I'm not sure how accurate your predictions need to be but if you simply plan on battery power in the next ten years I'd say you won't be disappointed. Capacity has been increasing, price has been coming down, and new chemistries are being developed all the time. I think we are seeing a real battery revolution happening here with more money being poured into it than ever before. An example in the basic LiFePO4 prismatics, the 160 ah cell size from last year now holds 180 ah in the same size and weight casing AND has a higher discharge rate, for a lot less money.
     
  19. bobw

    bobw Tesla Reader

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    Tell it to Mark Twain!

    A Connecticut Yankee in King Arthur's Court, chapter 27, on prophesy.
     
  20. vfx

    vfx Well-Known Member

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    #20 vfx, Aug 6, 2009
    Last edited: Aug 6, 2009
    All the crap I spew out on these pages and this is controversial?
    :rolleyes::biggrin:

    On topic.

    The feds just dropped another 2.4 Billion in battery research and manufacturing.
     

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