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High state of Carge in Sub Zero Temperatures

Discussion in 'Model S: Battery & Charging' started by randvegeta, Mar 7, 2018.

  1. randvegeta

    randvegeta Member

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    I'm doing a bit of travelling now and don't have access to an outlet that I can plug in over night.

    The temperatures are about -5C and I have a long journey tomorrow.

    I've decided to charge my car up to 95% and leave it parked outside overnight near where I am staying.

    I know it's not good to charge above 90% very often, and I know that when charging to full, it's best to drive it pretty much right away so that the battery does not remain in a high state of charge for too long.

    But given my long trip and very cold weather, I wanted to get as much charge in as possible. How bad is it exactly to have a battery in a high state of charge and then freezing? Does the cold mitigate the potential damage? Or does it exacerbate the problem as is the case in extreme heat.

    Also, presumably 100% would be worse than 95%. But how much worse?

    I only really need 90% to reach the next charger comfortably, but I wanted that extra 5% to help pre-heat and pre-condition the car as I'm traveling with my family, who would not be willing to sit in a cold car :).
     
  2. FlyF4

    FlyF4 Member

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    #2 FlyF4, Mar 7, 2018
    Last edited: Mar 7, 2018
    Uh, great question, but before we get to a direct answer to your question, their can be a bigger issue. When you say you only need 90% to reach the next charger, how are you determining that? Have you driven the route in these conditions before to verify? The reason I'm asking is because if you will be driving in very cold conditions, then you are going to lose a lot of battery due to the cold conditions. The first part of your trip will lose at a higher rate and the car batteries warm up due to the normal operation of generating power for the car. On a long trip in cold weather, you could lose 20% to 30% average range as quoted on the car at the beginning of the trip. is this something you are aware and have you factored that in?

    Oh, and is there anyway you can run a 15 amp extension cord and use the travel charger to keep the car plugged into an 120Vac outlet overnight even though it is outside? The car will do what it needs to keep the batteries in a safe state. Consider turning OFF range mode over night to allow heating of the batteries if needed. I don't know how cold you are talking about. You say -5C. I assume that is the low over night?
     
  3. randvegeta

    randvegeta Member

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    My car is a 2014 S 60 with about an 15% battery degradation. I have about 50kwh of usable capacity (not including the buffer below 0).

    The distance to the next charger is about 170km and am using an estimate of 200wh/km (sorry for using metric). Basically I need about 34KWH just for that distance, which is about 70% of my pack. But as you mention, I'll probably use more energy to begin with as I'll be starting cold, so I wanted a reasonable sized buffer.

    I'm taking the same route back as I used to get here, and I've done this journey a few times before (though in different weather conditions) and I know roughly what to expect with regards to energy consumption. I could drive slower to squeeze more range if need be, but I wanted this to be a comfortable trip with reasonable speeds and reasonable temperatures and with reasonable buffers.

    I figure I'll charge to 95%, wake up in the morning with 90%, pre-heat for 20 mins, maybe down to 85% and then use 70% to get to my destination, which would leave me with about 15% of buffer.

    The rated wh/km is about 179. If I drive at 100km/h (60mph) with the temperature set at about 20C, then 200wh/km is about what I expect on a flat, dry highway. With a 15% buffer, my energy consumption could be upto 240wh/km and I should still be able to make it.

    If I only charged to 90%, then my buffer would be at most 10% and that is probably too little for comfort, especially since efficiency will decrease if it's raining or snowing. And my wife would not be happy :).

    Not really. I mean technically yes, but that would mean having the window slightly open in the apartment we are in, and that would mean making it freezing cold in the apartment, which is of course less than ideal.

    The temperature tonight is pretty mild. -2C right now, which is about 28F. But it can get really cold sometimes (-30C / -22F is not uncommon).

    I expect to wake up to a cold soaked car, with the snow flake icon and regen disabled. I hope pre-heating will take care of that. I've disabled range mode so the battery heater will come on. The pack heater and cabin heater could use 10kw? Run that for 20 mins and that's a good 3KWH gone, which is actually about 6%.

    Any way. I've done the calculations and I should be fairly safe for my trip.

    The question remains, is it especially bad to keep the battery in high state of charge in freezing temperatures?
     
  4. FlyF4

    FlyF4 Member

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    Sounds like you know your car well and really plan ahead. Fabulous, you think of everything, but I am more comfortable with the fact that you said you know the route and have done it before.

    At that temperature for that period of time, I would not worry about charging to that rate. I am not quite as knowledgeable about that exact condition so I had to defer to my Panasonic buddy for a thought on this.

    Have a great trip.
     
  5. randvegeta

    randvegeta Member

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    Ha! Thanks.

    Well I've read that cold weather can help prolong the life of Li-Ion batteries. I hope that also means that charging up to above 90% won't be so damaging and the cold may even provide some protection. But I'm just guessing here. I know keeping it plugged in is best as the BMS will do what it can to keep the condition as good as possible. But I have no idea what happens when you unplug and leave the car to sit in the cold for extended periods.

    I'm wondering how safe (or dangerous) it would be to let the car sit when the temperatures plunge to around -30C.

    This trip is actually a lot easier than it used to be. Where I live, in Lithuania, the charging infrastructure was much much worse just 1 year ago. There was a 220km stretch we'd have to cross without any access to fast charging. In the summer, it's not such a big deal, but in the winter, that's really cutting it close. Normally we don't charge above 90%, so for us, that means 45kwh of usable power. To do 220km on 45kwh means an average of 204wh/km - That's about 329wh/mi. Which I think anyone who lives in cold climate would agree, that's not exactly a lot. Not impossible, but it's not the kind of journey you can do without thinking about it. You need to really manage the speeds and temperatures. The additional charging stations the government have installed really makes life easier. The old chargers we used were in cities, meaning we would have to take detours off from the highway. The new chargers are all on the highway, which really is much more convenient.

    Long story short, I know the range is doable. It's more about making it more comfortable. Travelling with wife and baby, so there is no flexibility in comfort ;). If the Tesla can't make it, then we take the ICE car.
     
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  6. FlyF4

    FlyF4 Member

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    Thanks for the extra interesting info. Knowing how batteries react in a no-use state at freezing temperatures is outside my knowledge but my Pan buddy sitting here today says this question comes up a lot. He also mentioned something I was not aware. In very cold conditions as you mention, the batteries can use as much as 40%-50% more energy during the first roughly 20 minutes of your trip than on the rest of the trip and that is why he says you can average a 20% to 30% range loss over a long trip. Sounds like you knew that already from prior trips. He claims you are not going to lose any more energy than normal with the batteries just sitting there in the cold, but less energy is available for release until they warm up. And claims not an issue for that period of time or that charge as mentioned earlier. I assume you also know that IF you have heated seats, it is better to try and use them and reduce the cabin heater use.

    Don't hit any animals :)
     
  7. Rocky_H

    Rocky_H Active Member

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    I am pretty sure that doesn't happen. The battery heating from remote climate control only comes on if the car is plugged in. Since you are going to be unplugged, I think it will only run the cabin heating. Basically, that just seems like a waste of energy. Since you're going to be tight on energy, I wouldn't do any preheating if you aren't plugged in.
     
  8. FlyF4

    FlyF4 Member

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    thanks Rocky. Agree and that is why I asked if there was any way he could plug in over night, even if it is only 120V at house current.
     
  9. Rocky_H

    Rocky_H Active Member

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    I'm feeling pretty decently comfortable with the 95% idea. It seems like a pretty good balance between staying a bit away from 100% full, but needing lots of energy.
     
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  10. MorrisonHiker

    MorrisonHiker S 90D 2018.21.9

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    We've seen battery heating work when not plugged in. We tested it out when we first got 2017.50.2 and saw it working and indicated in the app...but only if we were not in the car.



    The above video mentions around 1:30 that it works whether plugged in or not and then shows it working later (but the car is plugged in).
     
    • Informative x 1
  11. Rocky_H

    Rocky_H Active Member

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    Ah, that's right. It was a little confusion in Electrek's initial reporting of that function.
    Tesla releases new mobile app update with battery preconditioning feature and more

    They did come around and find that plugged or unplugged it will still work.
    Battery Pre Heat Available in App now! | Tesla
     
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