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New/Refurbished Battery CAC

Discussion in 'Roadster' started by bart513, Jan 22, 2014.

  1. bart513

    bart513 Member

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    I've had my new/refurbished battery for about 2 months now and the CAC has been sitting at 154.61 steadily. I'm upset as I thought it should climb to about 160? I haven't range mode charged it yet which might help? The problem is for me to range mode charge, when I reach my destination I can only give it a trickle charge at 15A for about 8 -10 hours. Any ideas?
     
  2. marco2228

    marco2228 Roadster Signature #34

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    I heard an ESS in perfect condition has a CAC value of 156. I might be wrong, but the cells have a capacity of 2.25 Ah and there are 69 cells in parallel (in a brick ) which would be 155.25 Ah for the brick.
     
  3. wiztecy

    wiztecy Active Member

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    CAC of 160 is the highest the pack can go although there were a few packs when really brand new (not refurbished) that reached just a bit above that. My refurb'd pack actually climbed over 5 months up to 160 CAC which I was happy to see and I think its rare to find a refurbished pack to go that high honestly. It sat there for 2 months and then dropped down to 154.71 CAC where its at now. @160CAC I was at 188 ideal miles in std and @154.71 I'm at 185. I'm not too concerned and think the CAC and ideal miles may rise back up over the summer.

    You may find yours may rise in the summer as well, isn't it pretty cold where you're at now? That has an impact on the CAC.
     
  4. Doug_G

    Doug_G Lead Moderator

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    When my car was brand new the CAC was 157.28 but this gradually climbed. Extremely gradually. It peaked a year later at 160.02. Then it started trending back down again.
     
  5. bart513

    bart513 Member

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    It has been cold but even when we had warmer weather the CAC was the same. Maybe it will rise over time and when I have a chance to charge it in range mode?
     
  6. Doug_G

    Doug_G Lead Moderator

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    Very likely, yes.
     
  7. thefortunes

    thefortunes Member

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    My CAC has moved from 155.74 when I bought it at the end of August (with 12,500 miles) down to 150.33 at the end of October, then reached a new high of 155.15 on January 14th during the 'Polar Vortex' and is currently 154.14 (with 23,700 miles).

    My ideal range has varied from 186 to 181 and was back up to 185 this morning. It has correlated pretty closely with the CAC value.

    It is my theory that CAC is affected by the pack's balance status (although I'm not sure why my pack may go into or out of balance since I commute 110-120 miles a day and don't really change anything with how I charge). Any thoughts?
     
  8. Doug_G

    Doug_G Lead Moderator

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    I'm pretty sure CAC is affected by the pack's balance status. And I believe it's used in the algorithm that estimates your range.
     
  9. bart513

    bart513 Member

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    I'm going to take a long drive tomorrow after charging in standard mode tonight getting down to about 20% SOC. The plan then is to charge in Range mode for my drive home and see how the CAC is affected.
     
  10. djp

    djp Roadster 2.0 VIN939

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    Make sure you don't turn the car off during the long drive, it has to be done on a single key turn to recalculate the CAC. The update happens after a full discharge and recharge cycle, so check after the Range charge finishes.
     
  11. wiztecy

    wiztecy Active Member

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    I have to think differently, unless there's another term used for balancing the pack. But if its the same balancing that's in the Tesla Diags Balancing grid in Diags, I've seen no correlation. My gird is always 0's and the only time it wasn't was when I had to balance the pack out initially after receiving the Refurb'd pack that was sitting at a 50% or lower SOC for some time. If someone is charging up to at least std mode and allowing the pack to balance for at least 30-45 mins their pack most likely is fully balanced unless they've been doing lots of short charges below 80% and neglecting to allow it to sit above 81%.
     
  12. bart513

    bart513 Member

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    OK. So 2 nights ago I did a 95% standard mode charge and drove 135 miles in 11 degree weather trying hard NOT to use the heat, only the heated seats. It was a chilling experience and almost froze my toes as everything was layered. Then I did a range mode charge for the first time on this battery 99% SOC getting Ideal Range of 245 miles (!!!) and Est range of 195 miles. Drove back home 135 miles with only 1 key turn (as per Wiztecy) in peace and harmony using the heat the whole ride home. Last night did a standard mode charge 95% SOC and the CAC was still at 154.61:( I was hoping it would go up and feel that the new/refurbished battery CAC should be higher. Am I off base with this?
     
  13. Doug_G

    Doug_G Lead Moderator

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    Well, you got 245 miles so call it a win!
     
  14. wiztecy

    wiztecy Active Member

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    245 RM is great! Also its 11F outside you said, CAC does sink down in the winter and climb back up in the summer as people have reported. I'd be happy with the CAC. You can have that same 154.61 for 25,000 miles if the whole pack is healthy really and that's what really counts, longevity of the CAC and relative consistency. You also could have a 160 CAC and then have it drop down to 150 CAC in 25k as well.

    Again I wouldn't worry too much about it and actually be happy since your RM came in very healthy. What did you std. mode charge come out to this morning?
     
  15. bart513

    bart513 Member

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    Thanks Doug and Wiztecy for the vote of confidence on the CAC as I was a little worried. FYI the battery was charged in standard mode in my garage which was about 36 degrees F. This morning the std mode charge at 95% SOC was 183 miles Ideal Range and 160 miles Estimated Range (given my driving in the cold and using the heater I assume).
     
  16. bart513

    bart513 Member

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    Does anyone know the reason why it's bad to charge in Range Mode too frequently and what is too frequently? In this cold weather I can't make it to NJ in standard mode without using the heat for the 3 hour drive.
     
  17. djp

    djp Roadster 2.0 VIN939

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    The electrolyte in the battery breaks down at high SOC and high temperatures. Charging in Range mode isn't that bad, but letting it sit there will degrade the battery, especially in the heat.

    Don't worry about doing a Range charge if you drive the car immediately after the charge finishes. The cold weather will also help protect the cells.
     
  18. bart513

    bart513 Member

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    So if I range mode charge 1-2 times a week it's fine as long as it's cold and I drive off soon after the charge is completed? This won't degrade the battery at a faster pace?
     
  19. djp

    djp Roadster 2.0 VIN939

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    Very marginally. The biggest factor in degradation is miles driven (ie. number and depth of charge cycles).

    High SOC and high temperature shortens the calendar life of the battery. You don't want to let it sit in those conditions for very long.

    If you don't store the battery in the heat at Range charge, then cycle count/depth becomes the main factor in capacity loss instead of calendar life.

    Based on Tom Saxton's study, Roadster batteries are averaging 10-15% capacity loss after 100,000 miles. The study didn't pick up any loss from battery age alone, which suggests that calendar losses from high SOC aren't an issue for Roadsters.
     
  20. dhrivnak

    dhrivnak Active Member

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    I would be more than happy to swap battery packs as I never saw a CAC above 150. Fortunately it has been stable over 2.5 years though.
     

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