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Concerned about battery degradation and "vampire" charging in Arizona during summer.

Discussion in 'Model S: Battery & Charging' started by BilliardsGuy, Jan 17, 2013.

  1. BilliardsGuy

    BilliardsGuy Member

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    In the Phoenix area the low temperatures in July, August can be 90 degrees. The battery is supposed to be actively cooled - does this mean that a Tesla parked in a garage will be running its refrigeration cycle 24 hrs a day to maintain a 75 degree or thereabouts temperature? What energy consumption will that entail? Also - if parked outside in the peak daytime temperatures of 120 degrees or more in the sun what will that require just for cooling (of the battery) and also what will it do to battery life? Then there is the need for climate control cooling of the occupants; any expectations of mileage drain for A/C?

    I've seen lots of issues on the forum due to cold weather but not much regarding very hot weather.

    I'm on the fence as far as a purchase because of these concerns. Are there any Az owners of the roadster that have experience with any of these issues? I don't think anyone has had one through this last summer.

    Any info will be appreciated. I'm an early depositer but a late decider.
     
  2. tdiggity

    tdiggity Member

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    It seems hard to say at this point because we're in the winter months. I did notice that in the teslamotors.com/goelectric page that you get more range @ 90 degrees!
     
  3. ElSupreme

    ElSupreme Model S 03182

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    This increased range is due to the less dense air at high temperatures. It is a big factor, much less drag due to much less air. It has nothing to do with battery cooling or other power draws.

    I don't think Tesla keeps the battery at room temp (75F) I think they keep it from getting really hot, and don't want it charging/discharging when hot. So just sitting I would expect 100F to be fine for the battery. When driving and charging it may lower the temperature of the pack.
     
  4. Puyallup Bill

    Puyallup Bill Member

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    A bit off topic, but battery temperature certainly does affect range. The LEAF does not have battery heating or cooling - ask any LEAF driver that lives in the northern states how winter affects range.
     
  5. Doug_G

    Doug_G Lead Moderator

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    In my experience, the Roadster cools the pack if its temperature exceeds ~40C / ~100F. If operating it will use the air conditioner to maintain that temperature. If charging, especially in Range mode, it will try to lower it to room temperature.

    If stationary it usually just circulates the cooling fluid, although it will kick in the A/C compressor if it needs to (or so I'm told... the maximum temperature here falls a little short of 100F).
     
  6. jomo25

    jomo25 P4398

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    #6 jomo25, Jan 17, 2013
    Last edited: Jan 17, 2013
    So, I asked this specific question of one of my friend/former colleagues who owns a Roadster here in AZ. He keeps EXTREMELY detailed stats on his roadster. He measures very detailed Wall-to-Battery and Battery-to-Wheel metrics. And he has it graphed against ambient air temperature.

    As a Volt owner, I was shocked by his experience over the last 2.5 years. In my Volt, I easily see a 25% reduction in range in the summer's heat as compared to the fall's nice temps. In the fall, I can get 45 miles per charge (on about 10.3 kWh) in the Volt. In the summer, that can drop as far as about 26 miles per charge, with essentially the same drive style. I attribute this difference to A/C usage and the Volt's temp mgmt system - liquid-cooled "like" the Tesla (I say "like" in parentheses for a reason - I'll explain). I dont keep the same kind of detailed records, so I can't verify my reasoning, but it seems rational.

    But my Roadster-owning friend said he sees a relatively small (only about 5%) battery-to-wheel difference in the summer in his range. And his data doesn't indicate a strong correlation between high ambient temps and range reduction. He did say however, he see a large (about 62%) impact and strong ambient temp correlation on the wall-to-battery numbers. Meaning he sees the charging efficiency drop quite a bit in the summer.

    So, how to explain this. Let's talk about the battery charging first. In our brief discussion of this, he said he believes the issue is that the Roadster's TMS works very hard to keep the battery in good temp range while it is applying the high current to charge. Indeed, when I parked next to him at the charging stations, I could hear the cooling system running while he sat in the sun charging. Sounded like an air conditioner fan running. Thus, the charging efficiency drops significantly because the car needs to work very hard to keep the battery temp in range while applying the 40A current (our work charge station is a 208V/50A 14-50 outlet). It'll be interesting to see if this is the case with the S. 62% is huge. Basically charging times would be 50% longer or more.

    There was a separate issue he had where the EVSE would stop working when ambient temps approached 118 degrees. The EVSE brick sitting in the sun in such conditions can reach a surface temp of 150 degrees, which seemed to trip it. This is an issue I've called Tesla about specifically regarding the Model S to which they replied this wont be an issue withe the S' UMC (based on learning from Roadster owners).

    Now, for the surprisingly small battery-to-wheel impact at high ambient temps. We could only speculate a few things:
    1. The A/C in the Roadster was much more efficient than the Volt.
    2. I ran my A/C in the Volt much more than he did in his Roadster in the dead of summer.
    3. The battery in the Roadster is much better insulated than in the Volt.
    4. The Roadster's TMS is much more efficient than the Volt's.
    5. The Roadster's battery pack's higher density/chemistry made it less impacted by high ambient temps.

    There may be others, but we figured it's likely a combination of the above.

    Now, will the S be the same? Will its shape (high surface area) exposed to the baking temp pavement make it more susceptible to the heat? These are big unknowns. BUt the evidence he's collected for the Roadster is very promising. I'm hoping it translates to the S. FWIW, I asked my Tesla rep these questions specifically. Of course, no detailed promises were made other than assurances that the S was tested in the heat of Death Valley and the S was "fine". Unfortunately, that doesn't say much.

    Anyways, I wanted to share this as some data to help answer the question. My friend sent graphs. I will ask if he minds my posting them (or if he's willing to post them).
     
  7. NigelM

    NigelM Recovering Member

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    Last week we had road temperatures in the 90's and on one day the temperature on my terrace read 111F. (Did someone mention global warning?)

    The car was parked outside a lot last week and I didn't notice any drop in range so if there was any it wasn't significant.
     
  8. mknox

    mknox Well-Known Member

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    I can only imagine this would be worse in Arizona, but my driveway can get extremely hot from the sun. Would simply parking the car over such a hot surface be a concern also? I realize the shade from the car will eventually mitigate this, but a lot of heat would be radiated upward for a while.
     
  9. kishdude

    kishdude P #130

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    I'm in Arizona and obviously I haven't had the chance to check high temp issues yet. My inclination is that if the car is just sitting parked, even in the sun since the battery is on the under surface of the car, the sun is not going to be a big factor. The asphalt will be hot if you just pulled into a parking spot, but the shade from the car should lower its temp to close to ambient fairly soon. I think that the critical period the battery needs to remain relatively cool is when the car is in use (moving) and when the battery is charging. Although the battery will need to be cooled when moving, I think this will require less energy relative to heating the battery in cold temperatures. It will also need to be cooled when charging which will require more energy to charge and will result in a slower charge.

    Speaking of charging, since on average I only drive about 50 miles per day, I've lowered my charge amperage from 40A to 15A since for my daily driving, at this amperage it takes about 6 hours to charge. This I hope will reduce battery wear and in the hotter months, will reduce the amount of cooling the battery will require during charging.

    Living in Arizona, I'm actually more worried about the 12V battery. As us Arizonans know, the heat does a number on 12V batteries and I don't think the system cools this. With the fact that if your 12V system is dead, the car will not operate and no easy way to "jump" it, this is more of a worry for me. I'm hoping that the monitoring system on the 12V will give me plenty of warning before the 12V fails in order to have it replaced before it dies.
     
  10. BilliardsGuy

    BilliardsGuy Member

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    Thanks for the replies to my questions.

    And I had not visited the "goelectric" tab recently with the estimates of range for various conditions - that was very interesting. I note that the dials only allowed ambient temperatures up to 90 degrees - what about 115-120 degrees! I drive from the Phoenix area to San Diego quite a lot and I was hoping for a SuperCharger to be placed in Yuma in which case I would be able to get there no problem - I thought!! But using the dials with a 90 degree ambient and with the A/C going and driving at 65 mph the range drops to 247 miles. But what if the ambient temperature is 115, with the A/C going (are you kidding!), I have a panoramic roof and I'm driving at 80 - 85 mph (my and everyone else's average speed on that stretch) will I even be able to get to Yuma? And then I have to recharge to go another longer but cooler stretch but that requires virtually a full recharge. Will the Tesla allow a full recharge - not just another 60 miles, but over 200 miles - in one SuperCharging session? Maybe the answer here is that the Tesla is not the way to go for long distance driving in hot climates. Most of my driving is actually local driving so not being able to do a Phoenix to San Diego trip in the dead of summer is not really a killer - I will just use an ICE for that type of trip, but it is a strike against my purchasing a Tesla for sure.

    I'm not an expert on LiIon batteries, but I have researched data on them to some extent and batteries do degrade faster at high storage temperatures and degrade if overheated when charging. I know Tesla says they have engineered this extensively and am hopeful they have verified their system in "Death Valley" or wherever.

    But I asked this question (effects of high ambient temperatures) to Bryan Bailin at Tesla Corporate and he informed me then about the active cooling system that would run and keep the battery temperature in an "optimum" range, and he specifically cited a temperature of 75 degrees. Now maybe that wasn't the exact design target, but if it is anything like that it will require battery resources on a 24/7 basis when minimum tempratures are 90 degrees or so and even more when exposed to direct sunlight parked on black asphalt - and even if the car shades the battery, the car itself gets really hot and the "ambient" inside the car is far above the ambient outside the car if left for some time.

    I wish Tesla engineering would jump in on topics like this and tell us the correct info. I'd like to know the basics of the battery temperature control algorithm and also to know the power drain figures under various ambient temperatures for both the battery temperature control and for human climate control. Inquiring minds want to know!!

    Thanks for any other input - Tesla Corporate can jump in here any time to straighten me out on these issues.
     
  11. dsm363

    dsm363 Roadster + Sig Model S

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    You may get less range during that extreme summer temperature but your battery should be safe. Unlike some other EVs, the Model S battery pack is tightly temperature controlled. The AC works very well from what I've seen so far (was only in mid 90s though when I got my car at the end of September so not a true test). Driving 85mph will be a much bigger hit on range than simply using AC so probably barely over 200 mile range with that.
     
  12. Doug_G

    Doug_G Lead Moderator

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    That's probably the wrong strategy. Tom Saxton did tests on the Roadster showing that the optimum charge current was somewhere around 30-40 amps. Speculation was that cooling the pack for an extended period for the slow charge consumed more energy, and disposing of a lot of heat at high charging power did the same. So a moderate power level is the most efficient. This likely applies to the Model S as well.
     
  13. BilliardsGuy

    BilliardsGuy Member

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    Yes, I looked at the chart on GoElectric that shows range vs speed and if my 55 mph range with A/C is 284 miles, the range at 85 or so will be less than 200 miles, and that is at 90 degrees ambient. But it seems from the forum that actually getting a full charge is complicated. However for my trip, I can't actually go 85 for the entire trip, but during the time I am unable to do so, it is more like city driving. So it seems I need to drive at a cooler time of the day (actually I usually do) and a little slower. But the recharge issue is still a big question mark - especially since they haven't announced a Yuma SuperCharger station.
     
  14. drees

    drees Active Member

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    Volt cooling:

    Parked, plugged in and SOC > 75%: Pack cooled to 72F, warmed to 25F
    Parked, NOT plugged in and SOC > 75%: Pack cooled to 86F
    Powered on: Pack cooled to 72F, warmed to 25F

    gm-volt.com: Volt thermal management system temperature band?

    If you lose a very large amount of EV range in your Volt in the summer, I would guess that your commute goes something like this:

    Unplug Volt in morning, drive to work so that SOC is < 75%.
    Car bakes in AZ heat while unplugged.
    Drive home, Volt works overtime to cool the pack back down to 72F consuming lots of energy.

    There's a way to read the pack temperature in the Volt, would be interesting to see how hot the pack gets before driving home.

    The only way to avoid the large reduction in EV range in this scenario is to plug in while at work. I'm kind of surprised that there isn't some sort of find-grained map that dictates pack cooling behavior that optimizes energy consumption and battery life based on more fine-grained temperature and SOC states. But perhaps GM found that additional complexity there only buys incremental improvements in battery life / energy consumption.

    Would be very interesting to compare the behavior of the Volt's TMS to Tesla's.
     
  15. jomo25

    jomo25 P4398

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    Did his analyses factor in ambient temps?

    - - - Updated - - -

    Actually, I do plug in at work. But I think the difference it makes is small. It helps, but I just count on a 20-30% reduced EV range. Not an issue obviously, more of an annoyance.
     
  16. drees

    drees Active Member

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    Hmmm - going from 45 mi EV range in regular temps to 25 mi in EV range in really hot temps sounds very extreme. Is that with pre-cooling using grid power as well? The guys on GM-volt.com don't seem to see as much of a hit (10-15% at the most) as you unless you are doing multiple trips on a single charge where the car has to cool down the interior multiple times after baking in the sun...

    Anyway, it will be intersting to see how the Model S does in the AZ heat, but I have to expect it to do as well as the Roadster which is pretty well!
     
  17. Doug_G

    Doug_G Lead Moderator

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  18. Todd Burch

    Todd Burch Electron Pilot

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    We need a technical blog post from JB on this sort of stuff.

    Remember that? Back when Tesla did blog posts? :)
     
  19. jomo25

    jomo25 P4398

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    First of all, I am on GM-Volt. Second, no one in that thread really talked about range loss when temps are 115 or so. And I've lived in TX previously where it would hit the 100s. But 115 is a big difference. The spot at work isn't covered, so yes, the car does stay baking in the sun. And yes, it is a lot of shorter trips (I rarely drive 40+ miles in one stretch in my normal driving of the Volt). Plus factor in that I do have a yong toddler, so I really do have to use the comfort mode AC. If it was just me, I could use comfort a short while, then switch to econ. But with the toddler in the back, I pretty much need to keep the AC on comfort mode the full time.

    Anyways, to get back on topic, I sent a message to my Roadster friend to ask if I can post his graphs. Hes on vacation and will be back on Monday, so I dont expect a response til then.
     
  20. REM

    REM Member

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    Thanks for asking the question, BilliardsGuy and thanks for all of the information from jomo25. Being an Phoenician, I am also wondering about the effects of our lovely summer heat on the MS battery and range. Seems like more data is needed. (Wish I had been an engineer at times like this.)
     

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