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SOC vs power and torque output

Discussion in 'Model 3' started by insaneoctane, Aug 21, 2018.

  1. insaneoctane

    insaneoctane Active Member

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    I have so been wanting this data.. .thanks @MountainPass!

    Article
     
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  2. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    So basically the car has about 30% more power at 90% SoC than at 15% SoC at high speeds, but there's no difference at all below ~60mph because you're limited by the max torque the car can handle.

    So... in a 0-60 run, your SoC is virtually irrelevant ;) If you were going for 0-60 times, it'd actually be to your advantage to drive around for a bit to warm up your tires.
     
  3. transpondster

    transpondster Member

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    graph says km/h, although scale looks like mph
     
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  4. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    Pound feet vs. kph? Who uses units like that? I do really wonder if it's mislabeled.
     
  5. D3xDt3Reaction

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    Weird unit combination but km/h seems like what they meant - 11000 rpm at 147 km/h. Final drive ratio of 9:1 and tire diameter of 26.3” implies 96 mph or 153 km/h at 11000 rpm, which is close. Another way of looking at it is that 18000 rpm is top speed of about 225 km/h, which would be about 138 km/h at 11000 rpm - also fairly close to the graph. So max torque looks to be around 45 mph?
     
  6. D3xDt3Reaction

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    Also, from the article (emphasis added):
    “You always get the same amount of torque up until the point of peak power, and the lower the battery is, the lower the power caps off. Then, from that speed — which we have to figure out exactly, but it’s about 50 or 60 kilometers per hour — there’s a noticeable reduction in power.”
     
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  7. BestHand

    BestHand Member

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    Not really correct conclusion. There is a huge difference between car steady driving with 60mph speed and car accelerating from 0 to 60.
     
  8. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    Not according to these charts (again assuming that they meant mph and not kph - if they meant kph then up to 37mph). You run at max torque regardless of SoC up to that point. And honestly, try running at max torque *without* accelerating, I dare you ;)

    Even if they meant kph, SoC should only make a small difference on your 0-60 times. Quarter miles, on the other hand....
     
  9. MarkinArch

    MarkinArch 1st S.A.TX Non Owner TM3 Delivery

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    Excuse my ignorance as this is my first EV - what is the primary reason that the power is reduced at different SOC? Is it battery preservation? Range preservation? Does the battery actually have less power with less charge?

    Thanks in advance for educating me.
     
  10. MountainPass

    MountainPass Vendor

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    We use Metric in Canada, so KPH!
     
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  11. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    But you use pound-feet? *boggle*
     
  12. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    No, no, and yes. :)

    Also, cold batteries produce less power; hot batteries produce more. But heat decreases battery longevity. If I remember correctly, in normal operations, Tesla tries to maintain the battery at 30,5°C, and when the car is in storage, will start cooling it down if it exceeds 48°C (while it heats it at any temperature below -7,5°C).
     
  13. MountainPass

    MountainPass Vendor

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    We also refer to our height in ft/inches, weigh ourselves in lbs, and measure distance in how many hours drive it is!
     
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  14. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    Hahaha.... oh, Canada.... ;)

    (We have a couple non-metric things, but not many... off the top of my head I can only think of two: screen sizes and rims)

    Well then, kph it is. So SoC is irrelevant up to ~37mph / 60kph - so it'll have a small impact to 0-60 times, but not a major one. But obviously, if you're doing higher speed runs, you really want the higher SoC.
     
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  15. insaneoctane

    insaneoctane Active Member

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    Some of it is the pack voltage can slightly drop at lower SOC
     
  16. MountainPass

    MountainPass Vendor

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    Also keep in mind that there is a minimum allowable cell voltage. Once the SOC gets low enough that the battery sag from the ~750A draw pulls the pack voltage down close to the minimum allowable pack voltage, the drive unit has no choice but to reduce the power draw to keep the battery in its acceptable operating window.
     
  17. Daniel in SD

    Daniel in SD Active Member

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    The AWD and P seem to make significantly more power than the LR (trap speeds are ~9mph faster). How do they do that with the same battery?
     
  18. MountainPass

    MountainPass Vendor

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    Sorry I was not clear enough. I mean that if you try to ask for full power at low SOC, the big current draw would pull the voltage too low, and at some point the BMS will limit the power the drive unit(s) are allowed to command.

    I'm sure if you compare an AWD car at 15% SOC and a RWD car at 15% SOC, the power will be very similar!
     
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  19. insaneoctane

    insaneoctane Active Member

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    I wish we had 0-60 and 1/4 mile times at each SOC to turn this graph into something that more people understand quickly. Don't get me wrong, I love the graph....
     
  20. Daniel in SD

    Daniel in SD Active Member

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    It's interesting that the power drops off so much at higher RPM at all SOCs. For example the power drops from a peak of 325hp to 250hp at 11,000rpm at 90% SOC. Presumably this is due to the inverter/motor, not the max current out fo the battery, or it would indicate a massive loss in efficiency (and would require huge waste heat dissipation capabilities!).
    When are you guys getting a P3D? :D
     

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