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How much usable power does my 85d have

Discussion in 'The UK and Ireland' started by Cornish85D, Aug 10, 2016.

  1. Cornish85D

    Cornish85D Member

    Joined:
    Dec 27, 2015
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    Cornwall
    Good Evening All,
    I know that all of the 85kw is not available to power the car but I was very surprised today. I finished a trip with exactly 50% power remaining and had previously charged to 100%. When I looked at the trip stats I was amazed to see that my "power used since last charge" was just 35kw. This means that the accessible power is just 70kw.........!

    Does anyone know if this is the normal accessible capacity? I can understand that some power has to be held back but around 20% seems like a lot.

    Thanks for any guidance/comments,

    Chris
     
  2. cyberkryten

    cyberkryten New Member

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    Aug 20, 2015
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    Location:
    United Kingdom
    I spent some time trying to work it out when I got my P85D but it was variable when comparing % to kW even using the data VisibleTesla logged for trips.

    Some trips would give 70kW whilst others 78kW and one issue was that the car doesn't consider drain whilst not in use to be 'used' so you can be down on kW 'used' reported by the car because of that.

    The only real way to find out is to drive the car to as low a charge as possible and then calculate how much power got put back in which seems to be 75-78kW useable, depending on how brave you are and how close to zero you'll run down to.

    These days, I assume 1% is 2miles and it always keeps me safely in range. In the current nice weather, it is nearer 2.5m per 1% but when you get to freezing February best use the lower estimate!
     
  3. pbceng

    pbceng Member

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    Aug 9, 2015
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    Location:
    UK
    I have a 90D and after several thousand miles of recording the numbers off the dash 100%=75kWh which sounds in line with your 85D. Im presuming there is a buffer top and bottom plus some bricking protection (5kWh for each??) but I've yet to run from 100% down to 0% to see at what point it actually shuts down.
     
  4. lklundin

    lklundin Member

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    I am almost sure that you mean 'energy' which Tesla measures in kWh as opposed to 'power' which is measured in kW.

    For example a Model S 85D has a battery able to store 85 kWh of energy and able to deliver power in excess of 300 kW.

    If you integrate your power usage over time you get your energy change, so if your battery delivers 10 kW for 2 hours, its energy content has been reduced by 20 kWh.
     
  5. dh12345

    dh12345 Member

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    According to here........OWNER'S MANUAL COMPANION | Tesla Motors

    "An 85 kWh battery has 75.9 kWh of energy available to use. The remaining 9.1 kWh is reserved as a battery buffer to prevent bricking"
     
  6. lklundin

    lklundin Member

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    So 'bricking' means that an electronic device due to misconfiguration is irreversibly and thus permanently put into a stage where it is useless - except as a brick.

    Surely, it should not be possible to brick a 100k$ car by running its battery below 9.1 kWh.

    Can someone please explain ? (Apart from the fact that the above "owner's manual companion" is not authored by Tesla).
     
  7. WannabeOwner

    WannabeOwner Member

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    If I've understood your question correctly then part of the battery is "reserved" and not available for use, when driving, in order to prevent the battery being fully discharged, which would damage it. Similarly, the battery should not be fully charged and left in that state for prolonged periods, thus the dashboard "charge level" shows a limit of 90% for daily use, and above that, up to 100%, for "trips". If you leave it set to 100% for several consecutive charges then a reminder appears suggesting that you reduce the charge level. When I need to charge to 100% I try to time the charge to finish just before I leave
     
  8. lklundin

    lklundin Member

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    Right.

    So unless the battery becomes damaged to the point that the car can _never_ be even turned on again, it is incorrect to say that bringing its State of Charge below the threshold of 9.1 kWh will be 'bricking' it.
     
  9. arg

    arg Member

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    It would be incorrect to say that, but noone is saying it.

    What they are saying is that a portion of the capacity is reserved for bricking protection ie. precisely to ensure that it isn't possible to 'brick' the battery.

    So zero on the gauge corresponds to slightly more than zero on the true capacity (I'm not sure that 9.1kWh is the correct figure for the difference, but it's at least a couple of kWh).

    Hence when driving you get down to zero on the gauge and the car then progressively reduces power and finally stops, but at that point the battery is not in fact completely empty and contains enough energy to run those minimal battery management functions that can't be turned off for several months, allowing you plenty of time to recover the car and charge it.

    A different design that allowed you to drive until the battery was truly empty would risk bricking, since a combination of functions that can't be turned off plus the battery's natural self-discharge would then run it 'beyond empty' at which point it dies. Tesla did not adopt that design for Model S.
     
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