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Interesting finding about Range Mode

Discussion in 'Model S: Battery & Charging' started by David99, May 17, 2016.

  1. David99

    David99 Active Member

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    For a few weeks now I have been using TM-Spy, a little app that shows data from the Model S that is not available in the normal UI. Out of interest I was keeping an eye mostly on battery temperature. I was surprised to see how the car seems to warm up the battery quite a bit all the way to 105-110 F. Definitely well above ambient temperature. In those last weeks the temperatures here in Los Angeles were between 60 and 80.

    The app shows the temperature of the coolant going into the battery module and coming out. There are two separate sensors. It makes it possible to see if the car is trying to warm or cool the battery depending on what temperature is higher or lower. What I saw is when I started driving (after a few miles) the input temperature was always higher than the output, thus the car was actively heating the battery. The difference in temperature was small. Only 2-3 degree difference, but it stayed that way until the battery reached well over 100 degree F. It takes a while, so only on longer drives did the battery reach this temperature.

    I was surprised why Tesla decided to bring the battery up to such a high temperature all the time. After several days of seeing this I realized that I had turned on 'Range Mode' a while ago an forgot to turn it off. So I turned it off. Now I saw that the car doesn't seem to heat up the battery as much any more. The battery temperature still goes up when you start driving, but I can see that the input temperature is lower than the output so the battery just gets warm on it's own from use, but isn't actively been heated on top of it. Driving with range mode off I have never seen the battery as high as 105, which was the norm when Range Mode was on.

    To be sure I just did another test drive. After driving for 35 miles with Range Mode OFF the battery was at about 89 F. The input temperature was just 1 or 2 degree lower than output. I switched to range mode, and within 2 minutes I saw the input temperature climb up 3-4 degree over the output and over the next 20 minutes the battery started to warm up to 98.

    I highly doubt the car turns the battery heater on. I think what happens is that when in range mode, the car directs the coolant through the motor and inverter and then directly into the battery. The inherent losses of the motor/inverter are used to warm the battery to about 105. A warmer battery has a slightly higher capacity than a cooler one thus giving the car a touch more range. It makes sense to have a warmer battery when trying to get the maximum range.

    I don't have a lot of time to do all sorts of tests, so I'm hoping others with access to the CAN bus can do their own tests and hopefully verify what I found. I do believe when the battery is below a certain temperature, it will always start warming it up, regardless of what Range Mode is set to. The only difference might be that when Range Mode is turned on, the car will bring the battery temperature higher than without it. Maybe it is different with newer cars with dual motors. Mine is a 2014 RWD 85.

    I did read that Range Mode will prevent the battery heater (a separate energy sucking electrical heater) from coming on, which ends up being counter productive when the car is charging and plenty of power would be available.
     
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  2. GlmnAlyAirCar

    GlmnAlyAirCar Member

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    Interesting observation. I will check later today if I can reproduce your findings.
     
  3. scaesare

    scaesare Active Member

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    Interesting indeed.

    It would seem to agree with the "max power" setting (or whatever it's called), that can be used with Ludicrous mode in order to squeeze the most energy out of the pack... that appears to heat the pack up as well.

    I also believe that user okishira here also noted that internal resistance on the cells continued to fall as they got warmer up to relatively high point. That ultimately wastes less power.

    The question them becomes: if the battery performs better when warmed like that, and the heating is "free" waste energy from the drive unit, why does it not also do that for non-range mode operation? My instinct is that, while it's better for performance, it may not be as advantageous for longevity.
     
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  4. GlmnAlyAirCar

    GlmnAlyAirCar Member

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    My thoughts exactly. This would imply there are drawbacks to range mode other than cold feet.
     
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  5. zambono

    zambono Member

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    Could it also be that range mode reduces cooling both for the cabin and components to conserve energy thus it warms up
     
  6. David99

    David99 Active Member

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    Yes the internal resistance drops as the battery gets warmer. It helps with performance and it helps with efficiency thus range. But for sure keeping the battery warmer will increase degradation a little bit.

    According to Tesla Range Mode reduced the cabin heater and AC to save energy. I definitely noticed that driving in hot weather.
     
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  7. Canuck

    Canuck Active Member

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    I've done this a lot since I go on trips most weekends.

    I hope this isn't true but I can see the reasoning. If it is true, it would be nice to an icon in our dash alerting us when Range Mode is on, in case we forget, so we can turn it off when not needed.
     
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  8. David99

    David99 Active Member

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    I agree, it is definitely something you don't want to keep turned on all the time. But at the same time Tesla doesn't want the owner to be scared that a feature is 'bad for the battery'.
     
  9. supratachophobia

    supratachophobia Active Member

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    Is it actively heating it up or just not actively cooling it as much as it could have? In other words, is it limiting the cooling on the input side and the end result is a warmer battery?
     
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  10. Canuck

    Canuck Active Member

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    I don't think an icon showing it's on in the dash would scare the owner. Rather, the owner would think it's there because the heating and cooling of the cabin is less effective when it's on, so it's there just to make sure you really want it on to extend range.
     
  11. deonb

    deonb Active Member

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    It would be a good icon to have anyway just for that reason.
     
  12. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    The UI used to show "ECON" on the climate controls when in range mode.
     
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  13. GlmnAlyAirCar

    GlmnAlyAirCar Member

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    I seem to recall from photos of various diagnostic screen that have been posted to this forum that there is both an "active" and "passive" heating target (or is passive just for cooling; I don't remember). I would think it would only be the passive target that is raised in range mode.
     
  14. supratachophobia

    supratachophobia Active Member

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    Sounds like range mode in the long-term may not be the best for the battery. At least, based on information publicly available that batteries tend to not like higher temperatures. So the worst scenario would be a hot day, with a full battery, with range mode on.
     
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  15. David99

    David99 Active Member

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    That's exactly what I think.
     
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  16. David99

    David99 Active Member

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    Since the input temperature is 3-4 degree higher the output temp is lower after it went through the battery it can't be the battery warming up itself.
     
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  17. Canuck

    Canuck Active Member

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    Our Leaf (with no thermal management system) gets dramatically better range in the summer. It's amazing the difference a warm battery can make when it comes to range.
     
  18. mkjayakumar

    mkjayakumar Active Member

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    So i guess in that situation hopefully the battery will not heated even more, because it might already be hot enough to get the maximum range out of it.
     
  19. AmpedRealtor

    AmpedRealtor Active Member

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    I highly doubt that using range mode will have any negative impacts whatsoever on battery longevity or degradation. Tesla already warns you if you charge to 100% too many times, they do not have an aversion to warning the owner. I would have to believe that if range mode had negative impacts, we would receive a similar warning after using range mode too many times.
     
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  20. apacheguy

    apacheguy Sig 255, VIN 320

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    Right. Never ever use range mode. It bumps the passive cool target from 30 to 40 C. It's a stupid feature.
     
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