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New regen profile is LAME; can energy be dumped into heater?

Discussion in 'Model S: Driving Dynamics' started by cduzz, Jan 2, 2020.

  1. cduzz

    cduzz Member

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    So the new "don't blow up the battery" regen profile is aggressively lame.

    I guess I'm on board with not blowing up the batteries but now I'm going to wear out my brakes because I won't get full regen basically ever.

    To those who understand how these things work better than I do -- I imagine the battery heater is just a giant resistor submerged in coolant that gets pumped around; is there any way the energy from the regen process could be dumped into that resistor instead of just dumping (or not) the energy into the battery pack?

    Another nice option would be to dump some energy into the cabin heater -- situations where the battery is too cold to charge probably correlate nicely with situations where the cabin heat is on.
     
  2. beatle

    beatle Member

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    Full regen is in the 50kw neighborhood, while the heater is only 6kw. Even if this were possible, you're talking about only adding 6kw of regen which is not much to be noticeable.
     
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  3. cduzz

    cduzz Member

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    So probably 12% of maximum regen isn't an enormous difference in driving dynamics, it is infinitely more than what you get with a totally cold soaked battery. Especially coming from a manual transmission where there is some engine braking even in a high gear, there is a substantial difference between absolutely no "engine braking" and "a little bit". From a UI perspective, I think having a floor to provide consistency is actually really important.

    I think as important as maintaining some regen pedal feel is that when the regen energy goes into the battery heater, it warms up the battery faster such that the normal regen system can kick in faster (if in range mode) or with less battery power to reach proper operating temperature.

    Given how amazingly efficient these cars are, squeezing another 6kwh from somewhere back into the system would make a big difference in cold weather range. Certainly the opposite is true -- running with a cold battery and the battery heater on devastates range.
     
  4. doghousePVD

    doghousePVD My grandfather’s car

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    My understanding is that the regen already is used for battery and cabin heating.
     
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  5. Adri

    Adri Member

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    If that were already the case, then why doesn't the battery heater kick in and allow the regen to quickly reach 'normal' levels?
    Even with an outside temperature of 10 degrees celcius, 50 degrees fahrenheit, it takes my S85D more than 30 miles of driving for the maximum regen to be restored.
     
  6. doghousePVD

    doghousePVD My grandfather’s car

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    You battery weighs 1200 lbs. I’m impressed it can be heated from 50F to 110F in only 30 minutes.
     
  7. beatle

    beatle Member

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    The battery only needs to be about 66F for full regen. I'm not sure how cold the battery has to be in order for the battery heater to kick in, but it turns off long before it gets to 110F. Maybe 40F?
     
  8. Adri

    Adri Member

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    If I puncture a few battery cells, I can heat it much quicker to much higher temperatures..... :)
     
  9. cduzz

    cduzz Member

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    All I know is that on my car (a pre-facelift 90D) there is absolutely zero regen when the battery is icy cold.

    If there were even a hint of regen, the car would slow down on level ground, instead the car is like a curling stone.

    If the car is in range mode, it doesn't matter if the car's gone 50 feet or 5 miles, the car still has zero regen. No green on the display, no slow-down on level ground.

    After 10 miles there is a single tiny green pixel when I let off the throttle, but that's possibly because the internal resistance of the batteries has finally warmed up the batteries to be slightly into the "the batteries can accept a tiny amount of charge" zone.

    If it is possible, dumping regen energy into the battery heater would be a tremendous help because:
    • the regen behavior would be far more consistent (even when stone cold there would be a tiny bit of regen)
    • the regen energy would actually be doing something useful (warming the battery)
     
  10. SDRick

    SDRick Active Member

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    I was always hoping that regen force would be increased over time, not lessened.

    The change in regeneration protocol is unfortunate, particularly for those of us in mild climates who are used to a very consistent one petal experience.
     
  11. urilevi8

    urilevi8 Member

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    Would be nice, if we have more options for regenerative level. Of coarse, not to harm the battery and car systems. Something like from 0 (no regen) to 5 (max regen) to choose, so we can keep enjoy one pedal driving. Would you agree?
     
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  12. David99

    David99 Active Member

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    This discussion comes up every winter for the last 6 years I had my Model S. You can't dump 50-60 kW into the coolant. First, you would need a dedicated heater that can take that much power, then you need dedicated wiring for it. The coolant would get very hot for these shots moments. It's not a good idea to pump very hot coolant through a very cold system. It creates extreme temperature differences that are not good for the battery. It's a lot of extra hardware for a few moments.

    That has changed with the recent software. They raised the temperature curve for regen by 3 degree Celsius. There is a whole discussion about it. I tested it before and after the update and posted the results here:
    Not having regen after the last software update sucks

    The battery heater is active when the battery is below 8-9 Celsius. If you are heading for a supercharger, it will heat the battery up to 25 C.
     
    • Informative x 1
  13. cduzz

    cduzz Member

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    Yes I certainly agree you don't want to dump anywhere near full regen power into the battery heater, but if it normally takes 6kw and is currently not on at all because of range mode, it seems like it would at least be able to cope with 3-6kw while regen is on; that would provide a decent backstop against absolutely no regen and also put some energy into the coolant while not substantially changing things.
     
  14. David99

    David99 Active Member

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    Yes it could do that as the battery heater is already on the high voltage system. So any power coming into the battery could be used directly by the coolant heater. I have tested it many times. It does not. Same with the cabin heater. It is also fed by the high voltage system and draws up to 6 kW. Again, regen is not used for it. I guess it's not that simple. Both these heaters don't have a constant, specific power draw. Depending on the temperature of the coolant and air their power consumption changes. The car would have to modulate the regen power carefully to not exceed the power these two elements are using. That goes against the driver using the pedal to modulate regen. I guess regen would feel rather odd and it would change even with the driver keeping the pedal constant.

    This whole topic has been discussed over and over. There is no easy way to capture that energy if it can't go into the battery. I'm no expert on super capacitors, but they seem like they could help out in many situations. They could capture regen power and slowly release it to the heaters or store it for the next acceleration. Even in warm temperatures they could soften out high charge and discharge spikes in stop and go traffic. I think that would be beneficial for the battery health. But again, that would require a whole added level of complexity in the power train.
     
  15. cduzz

    cduzz Member

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    Not to beat a dead horse and I appreciate your response (I had no idea that this had been discussed before, but search terms around this weren't obvious) --

    It is clear the car can ask for a specific maximum amount from regen (and the assumption that the driver will turn the rest into heat via the mechanical brakes, if they actually wish to slow down). It is also clear that the car knows things like the temperature of the coolant. There is very likely some threshold where you can ask for non-zero regen to dump into the coolant heater with no risk to hot-spotting anything while actually still doing something useful to the coolant temperature.

    So a regen profile of "if in range mode and coolant below -5 c, ask for 1kw and send to battery heater; if between -5 and -1, ask for 1.5kw, between -1 and 5 ask for 3kw". Such a regen profile would be pretty constant from moment to moment because there is so much thermal mass at play and the energy levels are pretty small, but big enough to actually achieve some good WRT bumping up the battery temperature.

    I completely agree that operating the cabin heat from regen is probably a total non-starter because of the thermal mass at play. Maybe with a super-duper bottle where you run the heater off a resistor in a bucket of coolant on a private loop for cabin heat would allow it but then you'd really slow down cabin heat by using coolant instead of air to cool the cabin heater coil.

    And, course, tesla seems to have recently discovered something new about these 3-8 year old batteries given the recent changes in charging and heating, so clearly this whole process isn't all just well-known-engineering.
     
  16. beatle

    beatle Member

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    I think that may provide even more unpredictable behavior in regen, even with a small 6kw load. The cabin heat will not always be running 6kw full tilt, and you may have conditions where regen completely disappears again when the cabin is at the current setpoint and is maintaining the set temperature. I think the amount of braking force created by 6kw of regen will be pretty trivial - definitely not enough to get back to 1 pedal driving. The car already alerts you to changing regen profiles by popping in the energy display, alerting you to a different driving experience. Asking people to monitoring it constantly for changes in behavior is not really an option.

    In this case I don't think the juice is worth the squeeze.
     
  17. sorka

    sorka Well-Known Member

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    It already does this if you have the heater on.
     

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