TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC

Understanding the battery heater

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

  1. Andyw2100

    Andyw2100 Well-Known Member

    Joined:
    Oct 22, 2014
    Messages:
    6,542
    Location:
    Ithaca, NY
    Adding more information that I had not mentioned before. On Monday I started using TeslaLog. My wife had completed her trip to work by the time I did this, so Monday morning's trip--the one when the pack was coldest and the battery heater was most likely to be engaged--is not logged via TeslaLog. But both Tuesday's and today's trips were logged, and the battery heater was not used, (assuming TeslaLog is correctly displaying the battery heating, which I understand it is.) Tuesday's trip and today's trip were in almost identical conditions, with the cabin temperature set two degrees higher today, and my wife completing the trip in less time (so travelling faster) today. The only significant difference was yesterday's departure was about 90 minutes after charging completed, and today it was 30 minutes after charging completed. Today was more efficient. How would you explain that?

    I'm not trying to be difficult. I'm really trying to help us all understand all this better.

    If it would help, I can provide the graphs from TeslaLog for yesterday's and today's trips.



    DistanceRMTotalAverageCabinOutside
    WeatherDuration





    Date
    (Miles)UsedEnergy (kWh)Energy (Wh/mi)TemperatureTemperatureWindConditions(Minutes)






















    1/5/16
    53.96218.233868105HWClear64





    1/6/16
    53.95917.131870105HWClear60





     
  2. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

    Joined:
    Jun 21, 2012
    Messages:
    7,024
    One thing that's odd here is that I'm seeing battery_heater_on in my logs even with reasonable outside temperatures. For example, the latest record on 3/29/2015, roughly 10 am shows outside temp measured by car was 8.5 degC, which would be about 45 deg F. battery_heater_on was on for about 3 minutes while I was driving, battery_level was 98+ (range charge).
     
  3. Rocky_H

    Rocky_H Active Member

    Joined:
    Feb 19, 2015
    Messages:
    4,299
    Location:
    Boise, ID

    You seem to have missed the principle within your own link you posted. On that page about the Second Law of thermodynamics, look at the section that says “Second law: Refrigerator”. There is link in there that says “heat pumps”. Click that. Now on that page, look at the second box down that says “Air Conditioners and Heat Pumps”. In the description there, it says:

    “Air conditioners and heat pumps are heat engines like the refrigerator. They make good use of the high quality and flexibility of electric energy in that they can use one unit of electric energy to transfer more than one unit of energy from a cold area to a hot area. For example, an electric resistance heater using one kilowatt-hour of electric energy can transfer only 1 kWh of energy to heat your house at 100% efficiency. But 1 kWh of energy used in an electric heat pump could "pump" 3 kWh of energy from the cooler outside environment into your house for heating. The ratio of the energy transferred to the electric energy used in the process is called its coefficient of performance (CP). A typical CP for a commercial heat pump is between 3 and 4 units transferred per unit of electric energy supplied.”

    So that is how heat pumps can get an effectiveness that appears to be more than 100% efficiency from the perspective of how much heat energy you get in the location you want it. They are using the electrical input to mechanically move heat energy from an outside source. You are thinking of how conversion of energy cannot exceed 100%.
     
    • Like x 1
  4. apacheguy

    apacheguy S Sig #255

    Joined:
    Oct 21, 2012
    Messages:
    5,056
    Location:
    So Cal
    @Flasher - Depends on the active heating target. This value has oscillated between 7 C - 10 C in the firmwares. It is quite possible that with 8 C ambient the condition to trigger the heater would activate.
     
  5. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

    Joined:
    Jun 21, 2012
    Messages:
    7,024
    Ahh, gotcha. I would figure it would be higher than that, myself. Thanks.
     
  6. ArtInCT

    ArtInCT Always Learning

    Joined:
    Sep 2, 2014
    Messages:
    1,713
    Location:
    Southern Connecticut
    I was under the impression that the HVAC system, pumps, fans, radiant heating, seat heaters, steering wheel heaters etc are all on the 12 Volt side of the Model S.
    Is that correct?
     
  7. apacheguy

    apacheguy S Sig #255

    Joined:
    Oct 21, 2012
    Messages:
    5,056
    Location:
    So Cal
    Yes, I believe the coolant pumps and fans are 12 V. The condenser and battery heater are HV, however.
     
  8. green1

    green1 Active Member

    Joined:
    Mar 25, 2014
    Messages:
    4,548
    Location:
    Calgary, Alberta, Canada
    I beleive that the A/C and heater are on the HV, but that the rest is 12V (including the fans and such) I think of it as all the 12V bits in an ICE are still 12V, but the parts that are engine mounted are HV (ie the A/C compressor, and the heater core)
    (unless someone wants to correct me??)
     
  9. ArtInCT

    ArtInCT Always Learning

    Joined:
    Sep 2, 2014
    Messages:
    1,713
    Location:
    Southern Connecticut
    Ok, I do recall some really early posts from the 2013 era that did discuss the battery coolant and heater pump.
    This fluid pump is 12 volt.
    I would imagine there is a compressor for cooling with 12 volt fans.... you can sometimes hear these running at a SuperCharger or in your garage on hot days.
    But the heating element for the coolant... is there a typical 12 volt fuse for that or not?

    So we have a compressor and heating element which are High Voltage?

    If so can the battery heater element and compressor ever run when the Model S is turned off?
    I have read that the contactors are kept in the off position when the S is off. This is done for safety reasons.
    And there is a special pre-ON check of all systems prior to the contactors turning on.
     
  10. Andyw2100

    Andyw2100 Well-Known Member

    Joined:
    Oct 22, 2014
    Messages:
    6,542
    Location:
    Ithaca, NY
    I have an additional bit of information for people to chew on, for whatever that may be worth.

    I was leaving with my wife this morning, on a slightly different trip that I also track, so the numbers would not be directly comparable to the other numbers I posted. Also I was driving instead of her, and that alone probably changes things significantly, not to mention extra weight in the car, etc. So I won't bother posting numbers. But here's what's really interesting:

    I timed the charge to end just when we left, and we wound up leaving 11 minutes after the charge completed. The temperature outside was 14F. I'm guessing the temperature inside my unheated garage was in the mid-30s. I had no regen limit!

    I had preheated the cabin a bit, with range mode off, but my experience has been that in conditions like what I experienced this morning, the best I could have hoped for from that preheating would have been a reduction in the regen limit, not an elimination of it. I believe the reason I did not have a regen limit was because the pack heated enough during charging to avoid it.
     
  11. green1

    green1 Active Member

    Joined:
    Mar 25, 2014
    Messages:
    4,548
    Location:
    Calgary, Alberta, Canada
    How long did you charge before leaving, and at what charge rate? how long did you pre-heat for? and how long had the vehicle been cold-soaked for?
     
  12. ArtInCT

    ArtInCT Always Learning

    Joined:
    Sep 2, 2014
    Messages:
    1,713
    Location:
    Southern Connecticut
    #72 ArtInCT, Jan 7, 2016
    Last edited: Jan 7, 2016
    Andy:
    The information you related above is pretty much in line with the information that Cottonwood has stated in some related cold weather threads. He likens the pre heating of the cabin as an energy storage and savings technique, so that you do not have to use power to get the internals of the S warm. He also stated that the charge just prior to the departure was the best and most energy efficient way to warm the high voltage battery pack and minimize the amount of time in limited regen. As you may know Cottonwood lives in the mountains and would like to hyper-mile with every decline he encounters. (I on the other hand am in fairly flat ground).

    It seems to me that cabin pre-heating is a 12 volt exercise and only gets the traction battery warm via conduction or its role in recharging the 12 volt battery.

    I am wondering if the Ludicrous Max Battery function is supported when on shore power and simultaneously usable when the traction battery pack is being charged by shore power? This would be a great question for the Tesla California techs who will be training the VA technicians in the P85D -> Ludicrous upgrade.

    In any case one has to wonder how green this "preheating" is....? Burning grid kWh's to get quick regen? My grid kWh's are not inexpensive at all.... about 25 cents each delivered and taxed.
     
  13. RiverBrick

    RiverBrick Active Member

    Joined:
    Mar 23, 2014
    Messages:
    2,392
    Location:
    Mount Washington Valley

    I had to monitor energy use closely last Winter due to no Superchargers in the province, record-breaking cold, and frequent visits to off-grid parks. There appears to be a sharp uptick in consumption for trips of any decent length once the outside temperature drops below approximately 5F, even if you start with a battery temp of 60F or higher. I've always suspected it was due to the battery warmer kicking in and am somewhat skeptical that recuperation of losses from a relatively efficient drive-train are enough to keep the battery warm in severe cold.
     
  14. AWDtsla

    AWDtsla Active Member

    Joined:
    Mar 3, 2013
    Messages:
    4,240
    Location:
    NE
    It heats at ~6kw from HV. It is not from the 12V

    You can if you have dual chargers. With a single charger you will go from charge to draw from the pack for several minutes then settle on a non-relevant charge rate (plus or minus depending on external temperature.)

    There's a break-even point which I have yet to calculate, where the return from additional regen is greater than the cost of shore power. It's probably not much.
     
  15. Andyw2100

    Andyw2100 Well-Known Member

    Joined:
    Oct 22, 2014
    Messages:
    6,542
    Location:
    Ithaca, NY
    I charged 3:28 at 56 amps. The car had sat for just under seven hours before the charge started. I preheated for less than 30 minutes. I don't know exactly how long, as the car had reached the set temperature of 70 before we left, and had stopped preheating. I would guess it probably preheated about 20 minutes, give or take.

    It's actually not, Art.

    I'm pretty familiar with what both Cottonwood and Jerry33 have written about this. Unless I am mistaken, both agree with what I've observed myself previously and that is that the preheating can reduce but not eliminate the regen braking limit. Also I don't believe either Jerry or Cottonwood typically experience temperatures as cold as the ones I was talking about seeing this morning. If memory serves, Cottonwood has a heated garage, and Jerry lives where it just doesn't get that cold.
     
  16. RiverBrick

    RiverBrick Active Member

    Joined:
    Mar 23, 2014
    Messages:
    2,392
    Location:
    Mount Washington Valley
    For last Winter when it was literally -4F or lower at some point everyday during daylight, it was more than just a quickregen issue, but let's leave that aside.

    The green question is very valid, but of course depends on each owner's situation. I'm lucky enough to pay 4X less than you for kWh's that are over 99% from renewables. So it's a bit of a perfect storm, living on a slope in a hilly city where it gets extremely cold with no Superchargers available for most trips, yet electricity is clean and cheap. So, yes, max battery pre-warming would be a very desirable feature for me. However, I understand that overall it's not a priority for now. There will come a point when there will be enough customers in my situation to warrant TM addressing this, though.
     
  17. Andyw2100

    Andyw2100 Well-Known Member

    Joined:
    Oct 22, 2014
    Messages:
    6,542
    Location:
    Ithaca, NY
    I was partially right and partially wrong:

    So Cottonwood has seen a complete lack of regen limits, though that was before Version 7 firmware, and Version 7 of the firmware seems more conservative with respect to the regen limits (they kick in sooner, at higher temperatures than they did previously.) Also it's not clear whether or not Cottonwood typically experienced temperatures in the low teens or not.

    In any case, I really think this is a pretty interesting find for version 7, and very cold conditions.
     
  18. David99

    David99 Active Member

    Joined:
    Jan 31, 2014
    Messages:
    4,676
    Location:
    Brea, Orange County
    Makes sense. There is only so much heat produced by the drive train. If you are driving at 25 kW you might see 2.5 kW lost in heat which of course can't be all captured. When it gets extremely cold, additional heating will definitely be needed.

    - - - Updated - - -

    It does take quite some energy to heat up the massive battery and unless you go downhill quite a bit, you aren't going to see much energy come back from regen. So I think just from an energy point of view, it doesn't make sense to heat up the battery to where you get full regen vs lets say just half. Again, I believe Tesla did think about all of this when programming the battery temperature management and made it to energy efficient. I mean after all, they spent a huge amount of effort in making every aspect of the car very efficient. It only makes sense to follow the same idea when it comes to battery temperature.
     
  19. green1

    green1 Active Member

    Joined:
    Mar 25, 2014
    Messages:
    4,548
    Location:
    Calgary, Alberta, Canada
    Thanks, I have not had the same success in similar situations, however I can only charge at a max of 32A (NEMA 14-50 with the crippled Canadian UMC adapter) so perhaps the higher current is what did it for you?
     
  20. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

    Joined:
    Jun 21, 2012
    Messages:
    7,024
    It isn't. 6 kW @ 12V is 500A. That heater would have some monster cables attaching it at that current level. :) Conversely, 6 kW at HV is roughly 15-17A, which can be done on a much, much thinner wire.
     

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC