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Battery Health question

Discussion in 'Roadster' started by bart513, Nov 6, 2014.

  1. bart513

    bart513 Member

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    I have a refurbished battery for about a year now and the CAC is worse on this than on my previous 1.5 Roadster. Ideal miles varies from 179-183 and the CAC has gone down from 154.6 in December 2013 to 147.87 yesterday. Tesla SC said that it is because I'm not driving it for long enough distances or frequently enough which doesn't make sense to me. They also said the famous "Bleed Test" did not show any problems with any cells or sheets. Any ideas or should I not be concerned?
     
  2. supersnoop

    supersnoop Tesla Roadster #334

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    Pull the logs and run some reports to see if it's a single brick or the entire battery. My 1.5, which was CPO's a 14 months ago, has a CAC in the 147 range.
     
  3. wiztecy

    wiztecy Active Member

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    I had/have the same thing going on. CAC was great, 156.82 a couple of months ago, and then started dropping in the past month pretty fast. It started dropping fast when I didn't let the Roadster balance for 2 commuting trips. Started to take longer than the usual 1/2 hour. So I allowed it to balance 2 hours. Still had to balance more. Then allowed it to balance overnight. The CAC dropped down to as low as 152.83 and has recently bounced up to 153.50. Pulled the logs and brick #90 is the lowest brick that has been there longer than usual. #10 is the next runner up. The average brick of the pack is around 157-158. I know around this time that my CAC drops anyways for whatever reason. My ideal miles when at 157 CAC was charging to 184 ideal miles std, its dropped down to as low as 179, and I'm now at 181 @ 153.12 as of this morning. Will be keeping an eye on it, I can see it rotating that lowest brick out and bouncing back up. To me it seemed like the out of balance really threw the weak brick out of whack.

    I'd check to see how balanced your pack is after you allowed it to normally balance each morning, and if its not balanced give it some time, a day or so to fully balance. Then observe.

    And yes, get the logs.
     
  4. Habious

    Habious Member

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    So, I'm going to display my newbie stripes here and ask...

    A) What's "CAC"?

    B) How does one go about "balancing" (I assume the battery)? Is this something that should be done on a regular basis?
     
  5. hcsharp

    hcsharp Active Member

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    Calculated Amp-hour Capacity. An approximate measure of your car's battery capacity.

    Your Roadster pretty much balances itself automatically unless you store it without driving for long periods. There are a couple of threads on best practices for battery health but empirical evidence shows that following Tesla's directions is the best thing you can do. Tesla recommends plugging it in every night and avoid frequent range-mode charges.
     
  6. dhrivnak

    dhrivnak Active Member

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    I have an original 1.5 batter and my standard ideal miles has been slowly dropping and is now at 171. Tesla maintains the battery is fine and in looking at the battery it is hard to disagree. Plug In America It seems as if one should expect to lose about 2 miles/year or every 10000 miles, whichever comes first. I hope they do come out with the 400 mile battery at a reasonable price. It would greatly help resale values.
     
  7. jordanthompson

    jordanthompson 2010 2.0 Sport, VIN 0683

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    I am sure this has been discussed many times, but I have found that charging at 110v seems to balance the pack pretty quickly and easily. I generally do this 2-3 times a year and I get back most of my "lost" miles.
     
  8. bart513

    bart513 Member

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    So how do Ideal miles correlate with CAC or is the CAC not as important as the Ideal Miles?
     
  9. djp

    djp Roadster 2.0 VIN939

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    It's a direct formula:

    Ideal miles = CAC * 99 * 3.7V * SOC LIM / 230 Wh/mi

    Where SOC LIM is the minimum % State Of Charge across all bricks.

    CAC is a better measurement of capacity than Ideal Miles since it doesn't depend on State Of Charge.
     
  10. bart513

    bart513 Member

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    Thanks djp. That was my thought which is why I'm concerned about the low CAC given the battery is just a year old! It should have nothing to do with only driving it 5,000 miles during the year correct?
     
  11. djp

    djp Roadster 2.0 VIN939

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    To recalibrate the CAC you'll need to do a deep cycle. Start with a Standard charge (or Range charge), drive to below 20% SOC, and then charge back up to Standard. Try that and see if it helps.
     
  12. Jackyche

    Jackyche Member

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    If the vds service screen doesn't have indication that it's not balanced, is it fair to assume that the battery is balanced?
     
  13. djp

    djp Roadster 2.0 VIN939

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    The balancing grid only shows 1's when the BMS is running the rebalancing process, ie. directly after a Standard charge or Range charge. If the 1's take a long time to clear then you know the pack is out of balance. If they clear quickly then it's in balance.
     
  14. wiztecy

    wiztecy Active Member

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    Not true if you turned the key on before checking after a std mode charge, grid goes to all 0's even though its not fully balanced.
     
  15. bart513

    bart513 Member

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    I'm going to range charge to below 20% and then standard charge and see what the numbers are and will report back.
     

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