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Max Battery Power to Preheat Cold-Soaked Traction Pack? Possible? Pros? Cons?

Discussion in 'Model S: Battery & Charging' started by Andyw2100, Oct 19, 2015.

  1. Andyw2100

    Andyw2100 Supporting Member

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    #1 Andyw2100, Oct 19, 2015
    Last edited: Oct 19, 2015
    Until Tesla gives us a true traction pack pre-heating option, I'm wondering if it may be possible to use the new Max Battery Power mode to pre-heat a cold soaked traction pack from shore power to the point where there would be no regen limit, but then stop the heating before it got to the point where any degradation could occur.

    I think there are many questions that need to be answered.

    The first is whether or not Max Battery Power even uses shore power to heat the pack, or if it is set up to only use power from the pack, since it is intended to be used while driving. Can Max Battery Power be on and heating the pack while the car is off? Another question is does Max Battery Power somehow heat the pack faster and in a less healthy way than the way it is heated when it has to be charged, for example.

    Assuming it is possible and safe to begin heating the pack this way, another question is how to know when to stop the heating? Also since this option is not available, at least for now, through the API, in order to heat your pack using this mode you'd have to physically go to your car.

    If it's not possible to use Max Battery Power while on shore power, and/or while the car is off, is it possible to use it with Range Mode on? Why would we want to do that? Well, many of us with Ds keep Range Mode on because we want to maximize the benefits of torque sleep. But with Range Mode on, the pack won't be heated separately at all as we drive, so any regen limits are quite slow to disappear. We may be willing to use some power in order to get rid of the regen limits, while still wanting to maximize the benefits of torque sleep. A brief period of time driving with Max Battery Power mode on might accomplish this.

    There's no question that a more dedicated traction pack pre-heating mode would be simpler, and I have a couple of old threads going on that (see below), but in the meantime, I'm wondering what people think about the above.

    Suggestion for battery pre-heating and charge-end scheduling sent to Tesla

    Would you use battery heating if it were available?
     
  2. ArtInCT

    ArtInCT Always Learning

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    This is a very good question Andyw2100. What we all need to know, is that if MAX BATTERY POWER is invoked, and the car is on shore power, will the car use the shore power to do the conditioning.
    For instance in the winter in a cold garage.

    Also, do any of the APPs allow you to invoke MAX BATTERY POWER via a remote setting at this time or in the future? It will be inconvienient to have to go to the car to physically turn this on for many folks.
     
  3. AWDtsla

    AWDtsla Active Member

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    Yes it uses shore power, 5kW. If you happen turn on cabin preheat as well, your charge rate can become negative, I got it to go 2kW _draw_ from the battery and still 40 amps from the outlet while trying to charge. If you're going to start warming it and turn up the charge limit in order to go hooning around on a cold day, you're going to have to wait a long long time if you don't have a HPWC and dual chargers (I assume all shore power goes through the charger)

    With the pack probably around ~55F the estimate was 50 minutes at what seemed to be a constant 5kW draw. That's _a lot_ of heat.. Unlike people who tested before I am seeing a steady increase in max power while waiting for that 50 minutes to be up, 422kw, 428kw, 434kw (~80% SOC), and then I shut it off with another 15 minutes left on the clock since I was done driving. If I were to do it all the time my fueling costs would pretty much equal my gas car.
     
  4. StaceyS

    StaceyS Member

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    What I've done is turn on the cabin heater and raise the charge level. This causes the heaters to draw power from the battery, and the chargers to draw power from the grid. The car wants the battery at a specific temp for charging, so it will heat the battery as well. Doing this has been a fairly reliable way to get into a warm car with no cold weather related regen limits.

    I've got a P85, so the "Max Battery Power" option isn't available to me.
     
  5. Andyw2100

    Andyw2100 Supporting Member

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    Thanks, StaceyS.

    Many of us are pretty well-versed in the "traditional" ways to heat the pack. The problems with what you suggest that I had hoped might be eliminated through the use of the Max Battery Power option, and that would definitely be eliminated if Tesla simply provided a battery preheating option are that we are wasting energy heating the cabin when its not necessarily the cabin that we're trying to heat. Also in order to raise the charge level of the battery and start charging it would require having charged the battery to a lower level previously, which brings another set of problems: charging at possibly higher rates, possibly not having enough time to complete the charge, etc.

    Based on what I've read in other threads about what people think the Max Battery Power option may be doing, I'm not going to utilize it just to raise the pack temperature in an attempt to not have regenerative braking limits. I'll keep waiting--perhaps indefinitely--for Tesla to provide a dedicated battery preheating option.
     
  6. bradhs

    bradhs Member

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    Resurrecting this threat because it seems to be what I am asking... Let's say you are 15 to 30 minutes from a SuperCharger and want to make sure you charge at the highest speed. Battery is at 20%, you've got enough range to make it. Why not turn on Max Power and cause the batteries to heat up so that when you get to the charger you wont have to wait for it to warm up.
     
  7. skip8jj

    skip8jj Member

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    If you are driving to a SC, your battery will probably already be warmed up.
     
  8. AWDtsla

    AWDtsla Active Member

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    Yesterday I drove for 30 minutes at 75mph starting at 30F and still had limited regen until the moment I pulled into my garage. Imagine if it was 5F, or even colder.
     
  9. RDoc

    RDoc S85D

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    Not if you're staying in a motel with no charging and your car is cold soaked. We drove about 20 miles at 24F and were limited to 65 kW when we first plugged in.
     
  10. Andyw2100

    Andyw2100 Supporting Member

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    These two posts highlight the reason Tesla should provide the option to heat the battery pack to operating temperature (not to performance temperature), separate from the option to heat the cabin. I really don't understand why they haven't provided this functionality.
     
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  11. AWDtsla

    AWDtsla Active Member

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    They really don't think about cold weather usability, at all. They've done the minimum to protect the pack at freezing temps. Lurking on this forum and others the same things come up over and over and over, usually from new owners. Like why doesn't the damn steering wheel remember the heat setting? Why can't you defrost the car remotely? add another 20 or so trivial (for someone with access to source code) issues which just aren't right. I get the feeling that the only people with real feedback power are a group of core owners in California, where none of these things matter.
     
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  12. sorka

    sorka Active Member

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    Conversely, if you drive for 30 minutes starting at ambient 75F at 70 MPH, max battery will show ready if you enable.

    Also, after supercharging for 20 minutes, even when it was proceeded by a short trip, max battery will show ready even if it's really cold outside.

    I use max battery in the morning on shore power to check that the battery is warm enough for full regen. I've discovered that once max battery says it has 40 minutes left, then the battery is warm enough for full regen. If it starts out at say 50 minutes in my 40F garage in the middle of the winter, 10 minutes of max battery is enough to allow full regen.

    Given there are lots of normal situations such as driving for a while in warm but not too warm weather or supercharging for a while which will result in max battery already ready if you enable it, I doubt there is much harm to using.

    I would avoid using it at all if you're charged greater than 95% SOC.
     
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  13. AWDtsla

    AWDtsla Active Member

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    I don't think it's doing harm, it's just hard to control. How many minutes left indicates ready for full supercharging power at the SoC you will arrive at the supercharger? If only we had one of those newfangled computars to do that calculation for us.

    Really, it's the same deal with range mode and cabin heating in the winter. What temperature do I have to set the cabin thermostat so that it will achieve 72F and no more with range mode on? Oh let me get my sliderule out....

    edit - and LOL, I have to remember to turn OFF range mode so that the max battery heating will actually power the heater, or it will just sit there forever and do nothing.
     
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  14. sorka

    sorka Active Member

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    It would be nice to have an actual "preheat" option in the app that preheats the battery on shore power to the minimum temperature to allow full regen or even just to the point of allowing 50KW of regen as a little bit more driving should do the rest from that point.
     
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  15. AWDtsla

    AWDtsla Active Member

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    It should just compute the intercept to the supercharger and to the exact right amount of heating, all variables considered. It should also do the same estimation when it knows your destination, like where you go at 6pm everyday if you are at work, and that pack heating is futile, so don't even turn it on.
     
  16. Andyw2100

    Andyw2100 Supporting Member

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    I've made that request to Tesla, I think a couple of times, with threads here supporting the request. So far no luck.
     
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