oxy avatar image
oxy asked

Decreasing Peuker's coefficient decreases SOC?


I noticed that my BMV is calculating a too low SOC value (yes, it has been days since 100% charge reset), so I thought my currently set 1.05 Peuker's coefficient is too small for Tesla batteries. I adjusted it to 1.02 and to my surprise SOC instantly went down (?!) from 28% to 21%. Adjusted it back to 1.05 - SOC went back up to 28% again.

  1. To my understanding, adjusting Peuker's closer to 1.0 should increase SOC not decrease it, shoudn't it?
  2. Shouldn't the Peuker's coeff. be applied only during real-time? How is it incalculated into the SOC? Is BMV saving all historical Ampers that have flown through it since last 100% (I'd think that's highly unlikely)? If not, what's the formula? Consider that there's no temp. compensation, etc.
  3. Is there a situation where Peuker's coeff. of, say, 1.02 not only decreases capacity, but can increase it?
  4. Now I have set it to 1.0 to see how the SOC is being calculated without it. What params to use in BMV to make SOC calculation trivial as such (i.e. without no Peuker's, temperature, efficiency, etc. magic):

    (Consumed AmpHours / Battery Capacity) - 1

    If I do this calculation I get 30% SOC, which is closer to reality than currently reported 21% with Peuker's 1.0 and charge efficiency 98%.

Thank you for your insights!

BMV Battery Monitor
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edgargw22 avatar image edgargw22 commented ·


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1 Answer
Epicycler avatar image
Epicycler answered ·

I don't have an answer, just to add to your mystery. Peukert simply says that at higher currents there is less available capacity. Sometimes that is mistaken for lost capacity. However, if I discharge at high amps until voltage falls to "empty" I can then continue to discharge at low amps until really empty. The capacity is not lost, its just not available at high amps.

I'm surprised that changing Peukert has an effect on SOC. To know the effect on SOC and capacity the amps has to be known. I set it to 1 for my Lithium batteries to avoid having to second guess a hidden algorithm.

Higher current reduces efficiency. Which is different to Peukert.

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