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

If battery is too cold to charge, will regen be redirected to battery heater?

Discussion in 'Model S: Battery & Charging' started by sorka, Jan 2, 2017.

  1. sorka

    sorka Active Member

    Joined:
    Feb 28, 2015
    Messages:
    4,236
    Location:
    Merced, CA
    I'm leaving this morning for a long downhill trip. The battery is too cold to accept regen at all. My question is, will regen be redirected to other things using power like the heater and defroster(AC) if I turn those things on?

    The grade for the first 5 miles is good enough for about 15 KW at 20 MPH. If I can redirect that energy into the battery heater, I'll be able to get regen back much sooner and and not waste any kinetic energy.

    The last time I did this, I wasn't really thinking and regen was disabled for the first 60 miles of the trip which was mostly downhill.
     
  2. Lloyd

    Lloyd Well-Known Member

    Joined:
    Jan 12, 2011
    Messages:
    5,251
    Location:
    San Luis Obispo, CA
    The battery heater is limited to accept about ~5kw.
     
  3. skip8jj

    skip8jj Member

    Joined:
    Aug 19, 2015
    Messages:
    87
    Location:
    Portland, OR
    Assuming your car is plugged in, use your Tesla app to turn on climate control to heat the interior. Even if your car has completed its charge cycle, it will start drawing power to the battery for climate climate control and heat the battery at the same time. I find if I turn on the climate control 15 minutes or more before departure, regen will work, perhaps not full on but enough. We live on a hill too.
     
    • Like x 2
  4. pilotSteve

    pilotSteve Member

    Joined:
    Jul 14, 2012
    Messages:
    866
    Location:
    Vancouver WA
    yes but what about the OP's question? I recall discussions from two-three years ago when the "where does excess regen energy go" and it would be a nice enhancement (if there is wiring/switching to do so) to at least make use of 5kw of "wasted" regen energy.
     
  5. Lloyd

    Lloyd Well-Known Member

    Joined:
    Jan 12, 2011
    Messages:
    5,251
    Location:
    San Luis Obispo, CA
    It does, but only to the extent that the battery is calling for heat, which is a max of 5 kw. This is barely noticeable compared to max regen of 60 kw.
     
  6. Nietschy

    Nietschy Member

    Joined:
    Oct 2, 2016
    Messages:
    75
    Location:
    Austria
    why not just preheat with the app, loose 2 or 3% and get it back downhill with regen?
    so you have a nice warm car and you do not loose any energy AND you safe your brakes.
     
    • Like x 1
  7. sorka

    sorka Active Member

    Joined:
    Feb 28, 2015
    Messages:
    4,236
    Location:
    Merced, CA
    Why wouldn't I just use "max battery" which will heat the battery directly rather waste energy heating the cabin?
     
  8. sorka

    sorka Active Member

    Joined:
    Feb 28, 2015
    Messages:
    4,236
    Location:
    Merced, CA
    If you mean preheat the cabin, the amount of battery warming that occurs for the amount of energy you use is a fraction of what you get when you use "max battery" directly. Now if you don't have a performance model, then of course you won't have that option.

    As it turns out, the battery was warm enough to accept about 10KW of regen from the start so I was good and my several mile down hill trip wasted no energy on actual brakes. We had the cabin heater going as well which sucked up the few KW remaining above the max regen the battery could take. Once we got to the bottom of that first hill, the regen line moved to the 30KW range where it stayed nearly the entire trip down but was more than enough not to have to use brakes.

    It was in the mid twenties when we left but I'm guessing being plugged in all not on 110 AC was enough to keep it warm enough to not lock out regen altogether.

    It was snowing hard when we left and traffic was averaging about 20 MPH down to 5 MPH in really congested stretches.
     
  9. skip8jj

    skip8jj Member

    Joined:
    Aug 19, 2015
    Messages:
    87
    Location:
    Portland, OR
    I do not use "max battery" as my T does not have that option. As for preheating the cabin, It is better to preheat it with shore power rather than get into a cold cabin and use that many more battery electrons to heat the car while driving from cold start.
     
  10. Cosmacelf

    Cosmacelf Active Member

    Joined:
    Mar 6, 2013
    Messages:
    3,746
    Location:
    San Diego
    What is max battery?
     
  11. Drone Flyer

    Drone Flyer Member

    Joined:
    Feb 22, 2016
    Messages:
    607
    Location:
    Canada
    Mid 20's? You have no idea what COLD is! LOL!
     
    • Like x 2
    • Funny x 1
  12. davewill

    davewill Member

    Joined:
    Feb 5, 2014
    Messages:
    514
    Location:
    San Diego, CA, US
    I wouldn't expect so. I would think that the regen would be based solely on the battery state and any other draws would be considered incidental and not be part of the algorithm. Just a guess.
     
  13. AWDtsla

    AWDtsla Active Member

    Joined:
    Mar 3, 2013
    Messages:
    2,790
    Location:
    NE
    No. The main problem is there's only one high voltage bus. You cannot drive voltage to the high voltage bus without also sending some charge to the battery. Therefore if charging is disallowed completely, all regen is wasted.

    Now a clever engineer could shut off the high voltage contactors in the pack only under regen, but Tesla does not do this. I suspect contactor failure would skyrocket as well.

    edit - welcome to my every day drive December -> March.
     
  14. AWDtsla

    AWDtsla Active Member

    Joined:
    Mar 3, 2013
    Messages:
    2,790
    Location:
    NE
    I left the car outside for a day. Low of 20F, high of 30F during the day. Regen was completely disabled for ~10 miles, getting in the car at 6pm. Really really disabled, 0kW. I'd never really let the car cold-soak for that long before but I was surprised. I had left my car parked and took an ICE car to my destination (which in retrospect was a good thing), since there the overnight temp was -5F. Evtripplanner estimates in no way covered the amount of energy needed to heat the battery, and simultaneously lost in regen for the first 30 minutes of driving (I disabled range mode just to see how much battery heating it would take, 30 minutes before full regen even with air temp of 30F). Between that and cabin heating, probably a 3x hit on range. I think I'm done _trying_ to use the car for ski trips unless destination charging is guaranteed.

    Does anybody know what the actual cell temp of regen disable is?
     

Share This Page