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Remaining Range Calculation (Voltage?)

Discussion in 'Tesla, Inc.' started by NickF, Mar 11, 2017.

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  1. NickF

    NickF 75D

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    I know lots of other threads touch on this subject but I can't find a concise answer. Does anyone actually know how remaining miles is calculated? Is it simply based on pack voltage?
     
  2. mrElbe

    mrElbe Active Member

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    It uses Voodoo magic and secret incantations to come up with the remaining distance answer.
     
  3. NickF

    NickF 75D

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    It appears so.
     
  4. ShockOnT

    ShockOnT ⚡️⚡️⚡️⚡️⚡️

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    I would think so. That's certainly how we measure longevity of implantable defibrillators.

    Batteries have a very predictable discharge curve, especially when little cell variations are averaged out across a whole pack.
    It would make sense to map voltage to that curve to get "percentage" charge.
     
  5. NickF

    NickF 75D

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    That makes sense. Where it get's a little fuzzy is with my 60D (75 battery). Delivered (8 months ago) range was about 222 and now it 215. The only thing I can think of is that the "mapping" algorithm changed. Let's say 100% on the 60D is 80% on the 75D battery. For simplicity's sake lets say that is 8 volts out of 10 volts (I know it's really closer to 4) . Assuming my drop is due to voltage...this means at delivery had 8 volts and now I have ~7.8 volts. It could be true that the 75D battery may have degraded a minor amount, so lets say it went from 10 to 9.8. That is still well above 8. So I don't see how the 9.8 can factor in to the remaining range calculation. My car can't even charge to 100% of the 75 battery so it wouldn't know that. Charging to 8 volts should easily be attainable. So still puzzled as to why the drop 222 to 215.

    Please note that I don't care about range loss, I am just trying to figure out how the system is working...
     
  6. csanders90D

    csanders90D Supporting Member

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    The car also measures the amount of current in and out of the battery. The voltages mainly act as limits to prevent damaging the battery by over- or under-charging it. A degraded battery will allow less amp-hours of current to flow before hitting the voltage limit.
     
  7. idoco

    idoco Member

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    Unlike lead acid batteries where resting voltage is a good proxy for state of charge (SOC), for lithium ion batteries voltage is not a great proxy. The resting voltage is fairly constant between SOC ~10-95%. So knowing the voltage for an individual cell could mean you are about empty, or about full, or somewhere in between.

    Most battery management systems use a shunt to measure current over time (amp hours) in order to estimate state of charge. If you have a cell with a 100 Ah capacity and you measured removing 25 Ah, you should have 75Ah remaining. The algorithms for range estimates probably use Ah.
     
    • Informative x 1
  8. NickF

    NickF 75D

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    Thanks this is very helpful.
     

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