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Understanding the battery heater

Discussion in 'Model S: Battery & Charging' started by David99, Jan 4, 2016.

  1. Andyw2100

    Andyw2100 Well-Known Member

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    The question that may arise for me is whether or not I want to bump my typical 56 Amp charge to 64 Amps if it seems that 56 is not quite enough to provide for a consistent avoidance of the regen braking limit, but it turns out that 64 is.

    It will definitely get colder than it was this morning. And while departing 11 minutes after the charge finished was close to optimal, I think in general shooting for a 20-30 minute window is probably more realistic. Both of those things make me think that it might take the slightly higher amp charging to consistently avoid the regen limit. The question is, is it worth it?
     
  2. BrokerDon

    BrokerDon Active Member

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    I actually set the charge rate on our Tesla P85D connected to a 80A (100A circuit breaker) HPWC using the EV ChAMP app to minimize charging losses from the "waste" heat charging at 80A. Supposedly this is not only more efficient (less heat loss charging at lower Amperage charge rates) but also better for our 85kWh battery in our P85D.

    EV Champ typically recommends only a 10 to 25 amp charge rate based on our power company's ("SCE) WattBox 200 "virtually" separately metered Time-Of-Use SCE TOU-EV-1 rate plan which is approx. 11¢ / kWh from 9:00 PM to 12:00 noon. Definitely eliminates the HOT connector on our HPWC charging at 80A...and MUCH easier on our 80A HPWC, 100A HPWC circuit breaker, HPWC charging cable, and P85D battery.
     
  3. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Low outside temps offset the higher temps from full Amp charging. If I had a below 40˚ F. winter parking spot for my car, I would probably keep charging at 80 Amps and plan on charging finishing near departure time to minimize regen limits.
     
  4. Andyw2100

    Andyw2100 Well-Known Member

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    Thanks!

    Knowing that, I won't hesitate to kick things up a bit if it seems it will help.
     
  5. David99

    David99 Active Member

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    Another reason the battery pack isn't heated too much is probably because of the heat loss. The battery cools down by being in a cooler environment. The rate at which the battery looses energy (in form of heat) depends on the difference between the battery temperature and the outside temperature. The greater the difference, the higher the rate at which it looses energy, thus the faster the battery cools down. As a result, you need to put in more energy to keep it warm. Keeping the battery at 50 degree with an outside temperature of 30 uses much less energy than when the outside temp is 0.

    It all comes back to being energy efficient. You don't want to waste energy by heating the battery up more than it needs to provide reasonable driving performance. Anything higher would use a lot more energy with very little gain in range or comfort. Keeping the battery at a warmer state also requires more energy, again without gaining range. Quite the opposite. The higher energy usage to keep the battery warmer would just eat up range. Only when the battery temps drop to a level where regen would be drastically reduced and you know you are going downhill quite a bit and wouldn't be able to capture that energy, then it might be better to heat the battery more. But even in that case, you would have to get more energy back from the higher regen than you put in to get the battery warmer and the extra energy you need to keep at that level.

    All things considered I think it shows there are lots of good reasons not to warm the battery up any more than just necessary. Anything beyond that gets lost one way or another. Of course there are some cases where energy efficiency isn't the priority and it would be nice to be able to manually set the battery heater. But frankly I believe it would be overused and lots of energy would be wasted. JM2ct
     
  6. scottm

    scottm Version 9 software sufferer

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    Anybody slapped on some undercarriage insulation that covers up the battery pack yet?
     
  7. AWDtsla

    AWDtsla Active Member

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    It's been on my mind. A thermos for the coolant loop would help to. Like Prius's have.
     
  8. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    The car wakes up every so often. If it needs to run the battery heater or you use the App to precool the car in summer, then the contactors would be activated.
     
  9. GasKilla

    GasKilla No Gas Know Peace

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    So at what amp rate do you charge? How is that more efficient that letting the charger go at full load? Do you have numbers to know how much energy you lose at 80 amps vs. 10 or 25 amps?
     
  10. BrokerDon

    BrokerDon Active Member

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    Sorry I don't have numbers... Just experience with the HPWC charging cable getting HOT when I charged at 80A... And acknowledging the Tesla website shows adding 100 miles of charge at 80A is only 0.1 kWh more efficient than charging at 40A. Plus Lithium Ion batteries have been reported to last longer if they're recharged at lower charging rates. YMMV. Profession driver / closed course. ObamaCare won't raise your insurance premiums, lose your doctors, or cancel your insurance. LOL
     
  11. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    My understanding is that charging is efficient between 30 amps and 80 amps. Below thirty efficiency drops off significantly. If you have dual chargers and an HPWC, charging over 40 amps splits the charge between the two onboard chargers, which may increase their life (not that onboard charger life has proven to be a problem). Running at less than 80 amps (or 40 on a UMC) keeps the HPWC cooler.
     
  12. GSP

    GSP Member

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    I know Tesla has a lot of important fish to fry and a limited budget and staff. However I wish they would put this request at the very top of their software to-do list.

    GSP
     
  13. AWDtsla

    AWDtsla Active Member

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    They have more than 12,000 employees at a roughly $7 Billion annualized revenue rate.

    Say wut?
     
  14. hybridbear

    hybridbear Member

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    How in TeslaLog do you see if the HVB heater was on? I'm not sure where to find that data. It'll be interesting to see my results come winter. I park in a heated garage, but our temps in MN are so cold in the winter that I'm sure I'll see a lot of reduced regen.
     
  15. AWDtsla

    AWDtsla Active Member

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    Look for a ~5kW draw when idle.
     
  16. hybridbear

    hybridbear Member

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    In TeslaLog I only see logs of driving & charging events. I don't see logs of sleep. TeslaFI shows logs of sleep along with the range loss during sleep. I thought previous posts were referencing a way to see when the HVB heater is on during a drive.
     
  17. hybridbear

    hybridbear Member

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    Andy - how do you see in TeslaLog if the HVB heater was being used? I'm not seeing where it reports that info...
     
  18. David29

    David29 Supporting Member

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    Bjorn Nyland recently made a video to demonstrate this point:
     
  19. PaulS

    PaulS Member

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    Looks to me like they quietly pushed a change to battery warming in a recent update. Our car is set to charge nightly to the recommended 80% level and in the past few mornings I've noticed it to be about 5% less than that though plugged in. So it seems the system now pre-warms the battery somewhat... not enough to get full regen right from the start (as you guys point out above, that would be costly), but warm enough to keep it from being whatever they have determined to be "sub-optimally cold" when we start driving on a cold morning. What has me puzzled is why not replace that power from the grid, since the car is plugged in, so that I have the 80% charge we want when we start out in the morning?
     
  20. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    If you preheat from the App, it will use the grid. Also, folks, including me, have found that there is less apparent degradation if you change to 90% (maximum daily) rather than 80%.
     

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