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'Lectra Shave Special

Discussion in 'Electric Vehicles' started by IndyPendent, Jul 13, 2010.

  1. IndyPendent

    IndyPendent New Member

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    #1 IndyPendent, Jul 13, 2010
    Last edited: Jul 13, 2010
    Greetings,

    New guy here, interested in tapping the collective wisdom of some participants to this forum. I'm not an engineer or a solar panel geek. Here's the rough sketch:

    A Ralt RT-5 SuperVee can lap the Speedway at about 160 MPH with 180-190 HP. The new Delta Wing IndyCar concept vehicle has a cD at about half of that chassis (.24). Delta claims in the neighborhood of 220 MPH with 300HP... so let's take drag horsepower losses off the table for now.

    The Tesla Roadster motor is 288 HP, 215 kW. The existing ESS stores 56kWh. Doesn't that get me full power output for 15 minutes?

    I understand the Xtrac issue, and VOCIS has a two speed transaxle on the dyno right now which is designed to handle the torque loading. Antonov is developing a multispeed gearbox for a Jaguar Hybrid.

    Gearing the Tesla motor for 7100 RPM in top gear should maximize efficiency and keep the drivetrain temperatures within manageable levels, right? Plenty of air cooling is available!

    CPI lithium-ion polymer batteries do not have metal cases, and do not require a cooling system. First look suggests that ESS weight could be significantly reduced. It appears that the energy densities are comparable.

    Valeo supercapacitors are being road-tested in a Peugeot/ Citroen EV. They are 1/3 less in weight than batteries, and charge in seconds. If supercap banks can reduce the size of the replaceable battery pack, so much the better. Plug-in recharge for the supercaps during pitstop for tires and ESS change.

    I'm not factoring in regeneration, since the plan is not to lift. Perhaps a separate bank of supercaps is appropriate to store energy from decelerating during pit entry, and using that power to accelerate on pit out. Yellow flags increase the range.

    Funny to read that the S sedan will be engineered for a 90 second ESS change. I had a really quick way in mind to do this in the pits, and the absence of cooling system connections makes it even easier.

    That makes a rough sketch of a 600 lb. chassis, 250 lb. drivetrain, 750 lb. ESS and maybe 100 lbs for the PEM. Add driver and roll out at 1850 lbs. Very heavy, but a Tesla roadster accelerates just fine at 2700 lbs (plus pilot).

    The added weight of the ESS is going right at the center of gravity of the chassis, not outboard where the g loads will play havoc with the balance.

    So long as the chassis and tire dimensions don't have to be increased (which increases the drag horsepower loss) to handle the added weight, I'm still not seeing the problem. What did I miss?

    That gets me 20 laps at 200 MPH on fifteen minutes of power. If the range can be extended to 25 laps, that's a normal 7 stop pit sequence for a 500 mile race.

    Trying to keep this within the realm of exisiting technology, I'd be interested to read the fatal flaw in this logic or your suggestions to improve it.

    A Swift DB4 carbon fiber chassis with a smaller ESS would be an example of the first test platform. Other EV racers I have seen online are lacking several of the critical concepts listed above.

    Should I be getting charged up, or am I a parasitic drain? Thanks,

    Andy
     
  2. TEG

    TEG TMC Moderator

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    Seems like you are in the ballpark, although I think you would need more size & weight of Lithium-Polymer to get the same kWh of a Tesla pack. Tesla technology packs are more energy dense.


    CPI Lithium-Polymer cells
    ~95Wh/kg
    So, 56kWh=~590kg... = ~1300lbs. (compare to ~900lbs. for Roadster pack)
    Or a 750lb pack would be 340kg for ~32kWh...
    So maybe not quite the range / track time you predicted.

    You may also notice that power output drops off at lower states of charge.

    Constant max power output isn't the friendliest way to use your batteries. Cycle life could be impacted.
     
  3. IndyPendent

    IndyPendent New Member

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    Hi TEG,

    Thanks for jumping in so quickly!

    Here's the CPI chart:

    Lithium-ion polymer

    Operating voltage (V)
    3.7

    Energy density (Wh / kg)
    >100

    High current performance
    Good

    Cycle life (deep discharge)
    >1000

    Quick charge (hr)
    <1.5

    Self discharge (% per month)
    <5

    Advantage
    High energy and power density

    The Panasonic and Sanyo batteries have a better power/ weight ratio????

    Sorry, this lesson began on Sunday. Lots to learn, thanks for the help!

    Andy
     
  4. IndyPendent

    IndyPendent New Member

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    #4 IndyPendent, Jul 14, 2010
    Last edited: Jul 14, 2010
    Thanks TEG, I had some digestion time this morning and your point is illuminating.

    So the Panasonic cells are the best solution so far? I assume that was Toyota's conclusion? They are coming out to something like 137 Watt hours per kilogram, hugely better.

    Andy
     
  5. TEG

    TEG TMC Moderator

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    It all depends on your application. Sometimes power density is more important than energy density. Sometimes price per Wh is most important.
     

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