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Charge Stopping Early in High Temperatures

Discussion in 'Roadster' started by DeedWest, Jun 27, 2015.

  1. DeedWest

    DeedWest 2011 Roadster 2.5 Sport #1438

    Joined:
    Feb 5, 2014
    Messages:
    164
    Location:
    North Dallas, TX
    Hello all. I've experienced a strange phenomenon recently that I'm hoping to find more information about.

    I have a 2011 Roadster 2.5 (#1213). I've recently noticed a change in Ideal Miles when returning to use my car after charging. I periodically check the CAC level, and the number has actually increased, so initially I was not convinced the battery was losing health. I decided to set a timer and watch the car as it approaches the full 85% Standard Mode charge. Here's where I discovered what was happening.

    I live in north Texas. The temperatures have regularly been in the high 90's this past week. The car does as it usually does: the amperage drops from 40A (I charge using a NEMA 14-50) to a lower amount as it approaches the end of the Standard charge (usually 82% SOC until 85%). This is all natural. Here's where I've noticed the change.

    The car regularly kicks on the front A/C fans to cool the batteries in higher heat during charging. This is something I'm used to seeing, especially in the summer months so far (back in January/February, the car rarely did so). However, I sat in the car as it's trickle-charging, and noticed that the amperage jumps from 23-24, to as high as 32A when the fans kick on during the end of the Standard Charge. About a whopping FIVE seconds after the fans kick on, the charging stops, and "Done Charging" appears on the VDS. The only issue is, the car isn't done charging. It's easily 4-6 miles below the full 85% standard charge. When checking in the SOC tab in the diagnostics, the charge level reads 83%.

    I wasn't 100% convinced this was a recurring phenomenon until I clicked "Top-Off". The same thing happens again; charging starts, amperage gets to 20-23A, and suddenly the fans kick on, bringing it up to 30A. Click. Charging stops again. Perhaps the car won't trickle charge at that high of amperage, so it naturally shuts off? My question to the community is: has anyone else experienced this, and does anyone have any further insight? I'm not necessarily worried or thinking anything is wrong, but love discussions. Thanks so much in advance!
     
  2. Electric700

    Electric700 Member

    Joined:
    May 21, 2013
    Messages:
    988
    Location:
    Florida, United States
    Do you think this behavior happens every summer, and it's just something you missed up until now? If no one else has a similar experience, it may be worthwhile to contact Tesla about this. Something may be amiss if the fan and battery cooling are consistently starting near a charge level of 83%, and then the charging stops a few seconds after, reporting complete.
     
  3. GVTesla

    GVTesla Member

    Joined:
    Nov 15, 2011
    Messages:
    188
    Location:
    Netherlands
    What I'm about to write is a total guess, but I decided to share it anyway, just in case it might contain something.

    I usually see the RS charge to less ideal miles when charging with higher amperages (I use A's anywhere between 13 and 64A, depending location). Yes it starts 'trickle charging' at the end when above 16A, but the 'trickle' is usually higher than say, 13 or 16A and stops at lower ideal miles than when I charge at 16 or 13A. Somehow the RS stops earlier when the Amperage is higher (>16A) in an attempt not to stress the battery too much? I usually miss 2 to 4 ideal km's when charging @ 32A.

    What might be the case is that this algorithm also does an intervention when the total Amperage draw is above a certain level. Say, the algorithm allows for a 'trickle' charge of 22A but is programmed in such a way that it deems 30A total drawn current, too much for the battery. So maybe, as soon as it detects the 30A and finds out it isn't able to tone that down, it stops the charging?

    An interesting experiment might be to top-off with the Amperage manually dialed down to 13A or something like that and check whether it charges to more ideal miles then?
     
  4. DeedWest

    DeedWest 2011 Roadster 2.5 Sport #1438

    Joined:
    Feb 5, 2014
    Messages:
    164
    Location:
    North Dallas, TX
    @Electric700 - I've noticed it happening recently as the temperatures have stayed humid and hot overnight, which is typically when I charge. The fans run rather consistently during charge in higher temperatures, so there is no correlation between SOC level and fan usage. I've only noticed that the fan shuts off as the car begins to lower the amperage at the end of charging.

    @GVTesla - Thank you so much for your information! I thought of that earlier, but didn't have the time to sit and watch, until now. BRINGING US TO A VERDICT:

    I just finished a Standard Mode charge, which stopped early at 166 miles Ideal Range. Then, I dialed the max down to 12A, and the car went flawlessly to 175 miles; a perfect 85% Standard charge for my 2011 2.5 with 35,000 miles. Interestingly enough, the fan WAS on for a good amount of the charge, but the amperage did not exceed 12A. How neat!
     
  5. Botbldr45

    Botbldr45 Member

    Joined:
    Oct 11, 2011
    Messages:
    513
    Location:
    Sedona, Az
    #992 does not like to charge very completely when ambient temp is above 87-90 degrees. I have 38000 miles on the car and it usually stopped charging around 165 to maybe 170 miles. When we added a MS 85 my wife started getting upset because it gets pretty hot in the garage even at night. I did an extreme....... Added an attic fan set on a thermostat to come on at 85 degrees........ Yes it's on quite a lot! I bought a portable AC unit and insulated the walls. It rarely gets above 80 degrees at floor level now and IF I keep idea and actual miles close ...... I'm back to charging at and above175 miles in standard mode. No idea what the amp cycle is during charge but fans don't come on as often.

    For what it's worth.......
     
  6. jaanton

    jaanton Roadster NA #1026

    Joined:
    Jun 25, 2010
    Messages:
    312
    Location:
    Oakland, CA
    My observations are that charging does involve battery temperature in complex ways. I think different levels of charge involve the cooling system in different ways with the different charging modes. Range charging wants the battery cooler than standard. 85 deg seems to be an important target as whenever I start a charge in a short time the cooling system will bring the battery level down to that if it is higher. Then a series of shorter cooling cycles bring it down to 75 deg as the battery gets full.

    But the ambient temperature seems to be involved also. The cooling system seems to stop if the ambient temperature gets too high. I'm sure the cooling system does not work well when it's so hot. It seems to me that the system might decide to stop charging if the cooling system can not get the battery temperature into the right range in enough time.
     
  7. Tesla 940

    Tesla 940 Member

    Joined:
    Nov 2, 2011
    Messages:
    254
    Location:
    Long Beach, CA & Taos, NM
    I've had similar issues. Yesterday (Sunday) I was trying to charge between track sessions. It was ~95 degrees and no shade. There were times the car would only accept 12amps at 240 volts. The VDS did NOT allow any adjustment. In the late afternoon with some shade I was able to charge at higher rates but was concerned that I would get the dreaded RED flashing around the charge port. I skipped the last track session because I needed 100 Ideal Miles to get home and didn't want to wait hourS to replace the charged used in a few laps - FYI, my usage was as high as 626/wh/mile. :eek:
     
  8. augkuo

    augkuo Member

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    Apr 24, 2011
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    549
    Location:
    Berkeley
    Adiggs found that he could increase the amp rating during charging when hot by cooling the PEM down with ice bags :)
     

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