Battery and ultracapacitors.

edited November -1 in General
I am wondering if a bank of ultracapacitors is used at all to help protect the battery from the large current draws during acceleration as well as braking if regenerative braking is used. If not what system, or design of the battery, makes it so these large current spikes don't effect the battery's overall health and longevity?


  • edited November -1
    Nope. No ultracapacitors.

    Here's the spec page...

    It lists a "Drive inverter with variable frequency drive and regenerative braking system".
  • edited November -1
    regenerative braking system -- "system" is a very broad term here. Like "drivetrain" can mean multiple things. Still, if there are any ultra-capacitors in use, I would honestly look more closely at the super chargers.

    A) You want storage to handle the PV energy storage. It gives the arbitrage flexibility should energy companies decide to shift which hours of the day are most expensive.
    B) You want that storage to be flexible -- capable of thousands of charge/discharge cycles.
    C) You want that storage to act as your testbed for future energy storage options.
    D) You want it to be outside your competition's prying eyes.
    E) You want everyone to think it's just a network.

    Then you can think about putting it in future car models, homes, and public spaces. Otherwise your'e always going to be "behind the eight ball" of some design-by-committee standard.
  • edited November -1
    In hindsight to my own comment, there's probably more value in growing and improving that network than there is in the cars themselves. Getting that technology right is the no brainer replacement to the oil addiction.
  • edited November -1
    What I am trying to get at is with 0-60 in less than or around 6 seconds, I know there is prob about a 300 Amp draw on the battery. I am wondering how the battery can stand this kind of current being pulled from it.

    Wikipedia tells me there are 11 layers, each layer with 9 bricks ( so far everything is in series) and then 69 cells in each brick linked in parallel. My math would lead me to believe with a 300 Amp draw there is a 3.03 Amp draw per brick so a 44 mA draw per cell, which seems reasonable. The specks of the 1865 cell, correct me if this is not that cell that Telsa is not using, about 2200 mAh so 44 mA is only 2%.

    However the link below makes me think the battery configeration listed above is wrong, making all my calculations off.

    what i am getting it is how is the battery design, number of series blocks or bricks and parallel cell. With out this I have no way of analyzing current draw out of each cell.
  • edited November -1
    I am analysing possible solutions to current(Amp) spikes that cause battery degradation. I would like to look at Tesla's battery pack but it is hard to tell the exact configuration right now.
  • edited November -1
    Regarding capacitors, should the technology ever get perfected, they will quickly replace the battery for several reasons. Unlimited power, almost instant recharge, do not wear out or degrade (can fail )
  • edited November -1
    @Bueller17 - the cells are NCR-18650A (3.1Ah, 3.6V nominal, 2.5V-4.2V depending on charge level) and they can easily charge/discharge at up to 2C without any problem, or around 6A each. The battery voltage is ~375V, so that is around 104 cells in series, for a capacity of 1.1kWh. That means you need around 73 sets of these in parallel, giving you around 226A output at 1C. The non-perf 85 has a peak power output of 270kW or around 720A. However, that is the output from the motor, and doesn't include resistive losses in the wires or battery, which will be substantial at that power level (the internal resistance of the 18650A's are around 200mOhms so it is generating 20kW of heat at 1000A), so it is probably over 1000A. The perf version is 310kW peak output, so assuming it runs at the same voltage it might draw a peak of 1100A or more. The car isn't going to sustain that for long (even with liquid cooling, you can't dissipate that much heat in the batteries), but that is a temporary discharge rate of 4-5C.

    I don't know how this relates to the exact chemistry used in the Model S, but LiPos can easily handle 30C burst discharge rates (don't do that for more than a few seconds or you will have a problem).
  • edited November -1
    No. Capacitors have low energy density, and low volumetric density, meaning you would need far more space than is available to power the car any distance.
  • lphlph
    edited November -1
    I am curious as to why Elon is so enthuastic about the super capacitors. Maybe he knows somthing about their progress the we dont?
  • edited November -1
    They're great buffers, accepting and producing surges that batteries don't enjoy much. And they permit even quicker responsiveness.
  • edited November -1
    Also more efficient. Li ion batteries charge at 4.2V and discharge at 3.7V (fully charged)... there is a build in loss. Capacitors do not have that loss... Regen buffered in capacitors would improve the efficiency.
  • edited November -1
    A capacitor is simply two conductive plates separated by a dielectric (insulator) The closer you can get the plates (opposites polarity attract) the more dense the power, hence super capacitor. A fellow on you tube thinks he has figured it out, for me, that remains to be seem.

    There are some real neat things about capacitors to power cars. Also some problems, assuming the density problem is solved.

    On the plus side 1. Unlimited power, you can draw as much as fast as you want without damage or degradation. 2. The opposite is also true, you can charge as fast as your wiring can transfer the power. You would fill up as fast or faster then you could fill a gas tank. It will take a super station with a charged capacitor to transfer to yours or you would brown out city blocks. 3. They don't ware out, could last for many years.

    On the negative side capacitors can fail. They have near zero internal resistance, should a failure in the wire or in the battery occur it could be catastrophic. 85KWH of power discharged instantly (short) would probably vaporize the car and everybody in it. A 100 microfarad 200 volt radio capacitor will weld the leads together when shorted.
  • edited November -1
    Boy, some of you are not well informed. The UCLA discovery means the super super capacitor is a reality, inexpensive and scaleable. Doing some simple math it looks as though the weight will be dramatically reduced as well. Also, may even get 1000 miles or more from a charge.

    Its been a year now, how long until they are available in the car?
  • edited November -1
    Well, if the volume isn't too high, it's great. But I haven't seen any info on volumetric capacity yet.
  • edited November -1
    One other advantage I forgot to mention of capacitors is there efficiency. What you put in you get out, and heat is not a problem.
  • edited November -1
    Here is the link to the press release by UCLA on the subject:
  • edited November -1
    Supercaps are in use now in some transit applications. One would think that a small number to buffer the main battery against high discharge rates would be an advantage(?)
  • edited November -1
    Batteries store energy in electro-chemical form, Capacitors in static electric form. Each compliments the other. Batteries have limited charge/discharge rates but high energy density; capacitors are complimentary with high charge/discharge but low energy density.

    The advantage of extending battery life by using (a small amount of) ultra capacitors has been proven to DOUBLE the life of truck lead acid (starting) batteries.

    Here is a press article about the Excide/Maxwell Technologies collaboration.
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