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 or making a Paypal contribution here: paypal.me/SupportTMC

What happens to regen if the battery is at 100%?

Discussion in 'Model S: Driving Dynamics' started by e-FTW, Sep 22, 2015.

  1. e-FTW

    e-FTW New electron smell

    Joined:
    Aug 23, 2015
    Messages:
    619
    Location:
    San Francisco, CA
    I have driven Piuses/Prïï a few times, and had regen braking simply go off going down a long hill as the battery was already full. Had to use mechanical brakes to keep the speed in check. Those cars also have a "B" mode on the transmission selector to engage ICE compression braking, which I could have used.
    What happens if your battery is packed to the brim with electrons? Will regen braking go bye-bye when lifting off the go-fast pedal? Does the car smoothly transition to let you know what is happening?
     
  2. islandbayy

    islandbayy Active Member

    Joined:
    Feb 25, 2013
    Messages:
    2,015
    Location:
    Greendale, Wisconsin
    Car will say Regen Disabled, then you will need to use regular brakes.
     
  3. TEG

    TEG TMC Moderator

    Joined:
    Aug 20, 2006
    Messages:
    17,249
    Location:
    Silicon Valley
    All the EVs I have driven go back to plain friction brakes when the battery is 100% full. Some will do it when the battery is very cold too.
    That is one reason why I like to charge my LEAF to 80% instead of 100%, so I get regen right from the start.
     
  4. e-FTW

    e-FTW New electron smell

    Joined:
    Aug 23, 2015
    Messages:
    619
    Location:
    San Francisco, CA
    I live on top of a couple of massive hills. Will plan accordingly.
     
  5. sorka

    sorka Active Member

    Joined:
    Feb 28, 2015
    Messages:
    3,247
    Location:
    Merced, CA
    I nearly rear ended a car the first time I charged to 100% and headed out. I wasn't prepared for the car not slowing down with regen. Had to slam on the brakes.
     
  6. alwaysru

    alwaysru Member

    Joined:
    Jul 11, 2015
    Messages:
    82
    Location:
    Austin, Texas
    I reported a bug to tesla after the first time I went to 100 and then went down the steep hill by my house. No regen freaked me out. Whoops!

    Probably something a delivery specialist should mention or there should be more than a new dotted line showing "reduced" regen.
     
  7. cynix

    cynix Member

    Joined:
    Jul 7, 2014
    Messages:
    652
    Location:
    Sydney, Australia
    I think this behaviour is counterintuitive. If regen is limited, why not automatically apply some braking so that the deceleration remains the same?
     
  8. tstafford

    tstafford Member

    Joined:
    Jul 4, 2015
    Messages:
    790
    Location:
    Nashville, TN
    Yep. Regen is gone or severely diminished at high SOC. I'd never experienced it before - I have always charged to 90% including when the car was given to me at delivery. However I had the car in for service any they moved the charge limit to 100%. I didn't even notice when I pulled out of my garage. Surprised the crap out of me.
     
  9. LLWS

    LLWS Member

    Joined:
    May 21, 2015
    Messages:
    37
    Location:
    Woodbridge, VA
    Look closely at the speedometer for the dashed lines noting your current limitations. If you charge to 100%, you'll get a message about Regen availability and you'll note a dashed green line on the Regen scale.
     
  10. jimtelsa

    jimtelsa Member

    Joined:
    Mar 31, 2013
    Messages:
    246
    Location:
    Simi Valley
    Our Smart Ed is just like that
    With a full charge paddle shift regen levels dont work till it drops a bit

    My Volt is opposite
    It can go from 41 full charge to 60 on meter with regen on a long hill.......
    so I assume they dont max out the Volts battery pack
    Regen still works to slow down car but wont show any higher gains than 60
    Regen also works on Hold mode...just gas generator only....

    Wild

    this is good to know as I still wait for my Tesla to arrive
     
  11. gavine

    gavine Petrol Head turned EV Enthusiast

    Joined:
    Apr 1, 2014
    Messages:
    1,007
    Location:
    Southern New Jersey
    Great idea....
     
  12. mknox

    mknox Well-Known Member

    Joined:
    Aug 7, 2012
    Messages:
    8,552
    Location:
    Toronto, ON
    Same thing happens in the winter when it's cold. Re-gen will be limited (as shown by a dashed orange line on the power meter) all the way down to zero depending on how cold it is.
     
  13. mikeash

    mikeash Active Member

    Joined:
    Oct 26, 2014
    Messages:
    1,107
    Location:
    Fairfax, VA, USA
    Most hybrids and EVs do it like this, where you push the brake pedal to get the braking effect you want, and the car figures out the right application of regen and friction brakes to make it happen. The advantage is that everything just works the way you expect it to. The disadvantage is that brake feel is worse and you're never completely sure what the car is doing.

    Tesla seems to have made the conscious choice to have the brake pedal simply be the actual friction brakes, and the accelerator simply be the motor. This gives us more control and visibility into what's going on, but does make us work a bit more when the regen ability is lower than usual.

    Having experienced both (I had a Prius before the Model S), I think Tesla's approach is superior. But it's not without its disadvantages.
     
  14. Skotty

    Skotty 2014 Model S P85

    Joined:
    Jun 27, 2013
    Messages:
    1,440
    Location:
    Kansas City, MO
    Would it be possible to allow regen in the motor but then throw away the electricity somehow? (I don't know enough about it off the top of my head to know if that is reasonable) If so, I would think this would be the best approach to maintain brake feel without having to add the extra complication of some magic combined braking algorithm like some other hybrids use.
     
  15. mknox

    mknox Well-Known Member

    Joined:
    Aug 7, 2012
    Messages:
    8,552
    Location:
    Toronto, ON
    This has been discussed here in the past, and if you think about it, 60 kW of energy is a lot to have to control through sophisticated electronics and then bleed off in some sort of monster resistor, all of which would just add weight and complexity to the car.

    After you get used to it (I've driven through 3 winters where reduced to no re-gen is the "norm" before the car warms up) it really isn't a big deal. You just press the brake pedal like you would on any other car.
     
  16. jgs

    jgs Member

    Joined:
    Oct 28, 2014
    Messages:
    938
    Location:
    Ann Arbor, Michigan
    Worst of all, it would add a radiator. And a radiator grill. No thank you.
     
  17. Jaff

    Jaff Active Member

    Joined:
    Aug 15, 2010
    Messages:
    3,007
    Location:
    Grimsby, Canada
    Yep, agree Mike

    I think it is far easier for the driver to just acknowledge that a full battery = no regen then add a new, somewhat useless system to the vehicle...

     
  18. scaesare

    scaesare Active Member

    Joined:
    Mar 14, 2013
    Messages:
    3,928
    Location:
    NoVA
    I wish there were a set of auxiliary set of high-wattage restive heaters for the battery pack (either heating the coolant, or surface-style heating pads heating the pack directly) so that when regen is disabled in cold weather, the regen power could be dumped in to them, so the pack could be brought up to temp more quickly....
     
  19. jgs

    jgs Member

    Joined:
    Oct 28, 2014
    Messages:
    938
    Location:
    Ann Arbor, Michigan
    Now that (unlike the radiator idea I mentioned) seems like an idea with legs. It would also potentially be useful for preconditioning with shore power. One misgiving is whether the pack can safely absorb X0,000 kW of heat, though. My electric space heater is 1.5 kW and it gets pretty toasty. We're talking up to 40x that.

    Of course, a pack heater wouldn't help when charged to 100%, the other case in which regen craps out.
     
  20. scaesare

    scaesare Active Member

    Joined:
    Mar 14, 2013
    Messages:
    3,928
    Location:
    NoVA
    Just quick back-of-envelope calcs, assuming you wanted to use flat surface-style heaters:

    - I estimate the pack is ~7' x 5'. That's ~5,000 in^2

    - Dumping full regen in to a surface heater that size is 60KW / 5000 in^2 = 12W per in^2

    - That rate is less than the ~15.5W per in^2 for a standard battery heater like THIS, and also not constant

    - That's only 8W per cell of intermittent heat applied. There's also additional pack mass that would buffer this somewhat.


    I suspect you couldn't regen nearly enough to be concerned about overheating that 1200 lb mass in any reasonable time period... unless you were coasting down from the top of Everest...

    And to be quite honest, I'm not sure how much faster you'd really be able to heat a cold pack up with typical regen during normal driving... the main advantage might simply be not having to lose the braking feel when you let off the accelerator...
     

Share This Page