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Cold Weather Driving

Discussion in 'Blog Archive' started by Doug_G, Jan 15, 2015.

  1. Doug_G

    Doug_G Lead Moderator

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    I'm currently driving my Model S through its third Canadian winter. I thought it might be helpful to discuss some of my "lessons learned" about driving the Model S in the cold.

    IMG_2361.JPG
    Feeling a little cold soaked...

    Model S Performance in the Cold

    You can walk up to your totally cold soaked car, hop in, and drive away. You don't need to warm it up. It won't chug and cough like a gas car; it'll just glide away. The cabin heat will even come up pretty quickly. No fuss, no muss.

    That said, there are a few differences in the way the car drives after it's been sitting in a frozen wasteland (aka parking lot) all day.

    When the battery pack is below freezing the car will not permit charging, as this will damage the cells. One side-effect of this is that you also lose your regenerative brakes. This is shown by the yellow dotted line on the speedometer. If the car has cold soaked below freezing you may have no regenerative brakes whatsoever. Pay attention, because the car will really really coast - this can be very surprising the first time!!! You'll have to use the conventional brakes until the car warms up.

    IMG_1456.JPG
    The dreaded yellow line

    If the battery pack is extremely cold, you will also have a power limit. This isn't usually much of an issue because if it's that cold, it's hard to go full throttle without spinning the tires. Cold rubber on frozen pavement doesn't make for great traction. So this is really more of a curiosity than anything.

    The battery pack has a heater. It's necessary so the car can charge in the cold. When you start driving a cold car the pack heater turns on, and it can draw up to 6 kW. So can the cabin heater. Simply sitting at a stop sign you're drawing enough power to go over 40 mph. Fortunately it does get better as the car warms up!

    Cold versus Range

    When the batteries are extremely cold, there will be a little bit of range loss, which is shown by a blue segment on the charge bar. As the batteries warm up that "lost" range will come back, so it's not really lost! The car has to be very cold for this to happen.

    Obviously energy needed for heating reduces your range. If the car is cold soaked this can have a big effect on your total range. Starting out with a warmer car can make a big difference to how far you can drive. We'll talk about preheating in a moment.

    You will also experience reduced range due to increased aerodynamic drag. Drag moving through the air is the dominant impact on the car's range at any temperature - and it gets worse in the cold. Cooler, denser air is harder to push out of the way. There is also a small effect due to the tires having worse rolling resistance, but aerodynamic effects are much larger.

    (Tip: Safely drafting a large truck has an even more dramatic impact on range in the winter. Do not tailgate; keep a safe following distance and you will still see improvement. Note however that strong crosswinds will adversely affect the effectiveness of drafting.)

    Cabin Heat

    The Model S cabin heater has two (hidden) modes. If the drive train is cold, all heat comes via resistive heaters, which can draw up to about 6 kW. That's a lot of power.

    As you drive the car, the drive train will naturally heat up. Once that happens, Model S uses the drive train coolant to help heat the cabin. Essentially it takes waste heat from the motor and inverter and uses that to heat the cabin. This makes a huge difference to the power consumption - a fully warmed-up car will only need 1-2 kW to keep the cabin warm even in extreme cold conditions. In comparison, the original Tesla Roadster needs 4 kW to keep its tiny cabin not-terribly-warm using only resistive heaters. This is a big advantage of Model S engineering that Tesla never talks about!

    The upshot here is that cabin heater power consumption gets better quite dramatically after you've been driving for a while.

    Seat Heaters

    Seat heaters are essentially free. They use miniscule amounts power compared to the cabin heater. Use them liberally. Crank up the seat heaters, and lower the cabin temperature a little. You'll save a bunch of energy for driving.

    Shelter your Car

    I have seen huge improvement in driving range after parking the car in an unheated garage instead of outdoors. That's because even unheated garages are often significantly warmer than outdoors. Also being sheltered from the wind will help during preheating, reducing heat loss and increasing the effectiveness of preheating.

    There are multiple reasons why a warm car is better: warmer cabin, warmer battery pack, and warmer drive train. As I've mentioned, a warm drive train means less cabin heater power usage. Starting with a warmer car always helps!

    Range Mode

    Range mode reduces the amount of power used by the heaters. This is most useful if you're heading out on a long road trip and your car is cold soaked.

    Once the car is fully warmed up Range Mode doesn't really do anything - the power required to maintain battery and cabin temperature is modest. In fact if you preheat the car before you leave Range Mode doesn't do much of anything.

    Unfortunately Range Mode also operates when you're preheating the car. As we'll see below, preheating while plugged in prior to a long road trip will significantly improve your range. You want the battery pack and cabin nice and toasty. Unfortunately Range Mode gets in the way! It reduces heater power even though you're plugged in. The result is less preheat and more range consumed!

    Therefore my recommendation is that Range Mode normally be turned OFF. Use it if you have to start driving a cold-soaked car - in that situation it might just save your bacon. All all other times turn it off; otherwise you'll do what I do and forget it's on. Then you'll slap your forehead when you jump in your car and discover it's not as well preheated as you expected!

    IMG_1525.PNG
    Preheating!

    Preheating for Long Trips

    If you preheat the car using the remote phone App, it will turn on both the pack heater and the cabin heater. The pack heater only switches on if you prewarm via the phone App, not if you turn the cabin heat on from inside the car.

    If your car is plugged in, it will use electricity from the plug to do this preheating. Note however that you need a fairly powerful charging station; it could need up to 12kW and a 110V plug will only provide a tenth of that. The rest will come from your battery pack! You definitely want to use a 240V source.

    The first advantage you'll notice is that the cabin is toasty, and the windows have probably have melted out of ice and snow. The second thing you'll notice is that you have regenerative braking at about half power instead of zero. That's because your battery pack is a lot warmer.

    Most importantly, because your battery pack is closer to normal operating temperature, the pack heater won't have to work as hard. After driving on the highway for a while, simply drawing power from the battery pack will help keep it warm. That's free heat!

    The upshot is, preheating your car will hugely improve your initial power draw, and that means more range!

    One caveat - and this is a biggie - if you can't plug in, don't preheat!!! You'll just burn up power that would be better spent moving the car. In that case, hop in the car, turn on Range Mode, and drive!

    Preheating for Short Trips

    Short trips are a totally different animal. This is mostly about comfort and convenience. Preheating means a nice warm cabin, clear windows, and some regen right away.

    If you're plugged in, go ahead and do a full half hour preheat if you can. If you only have 5 or 10 minutes to preheat, go ahead and preheat. It will definitely take the edge off.

    If you're not plugged in then it's a different story. You could end up using quite a bit of battery power preheating. This is not just running your battery down; it's also using up a little bit of your battery's lifetime. My usual compromise is to prewarm the car for 10 minutes to make the cabin reasonably comfy, then off I go.

    I encountered the worst-case scenario for Model S range last winter by going Christmas shopping in extreme cold (below -20C). Drive 20 minutes, cold soak two hours, repeat all day. I used most of an 85 kWh battery pack in relatively few miles. The thing is, it's still pretty hard to run the pack down to zero this way; the stores would close before that happened. But it is one situation where the 60 kWh pack might be a disadvantage.

    IMG_1537.JPG
    Brrr!

    Window Fogging

    Firmware updates to the HVAC controls (and the improved dashboard vents) have fixed most of the issues I've had with window fogging in the past. The Auto mode handles perhaps 95% of conditions very well. For the other 5%, some simple adjustments will help.

    If your windows are totally frozen up, hit the defrost button twice so it turns red. This will melt out the windows. Don't leave it on full power any longer than you have to, because the cabin will get way too hot. Then the normal settings won't give you any heat until the cabin cools down, and your windows will fog up again!

    For normal defrost, hit the button once so it turns blue. This will direct air up to the windshield. If you start feeling cold, use the manual setting to put air on both your feet and the dashboard.

    Once the cabin is warmed up the fan speed automatically drops back, and in extreme cold and/or humid conditions this may not provide enough air flow over the windows. The solution is simple - manually increase the fan speed.

    (Sometimes I'm lazy and just up the cabin temperature a bit, because the control is easier to access. But don't do that if you're pushing the car's range limits, the fan is cheap; heat is expensive.)

    In very extreme icing conditions, it may be nearly impossible to keep the window clear of freezing rain. This isn't a problem specific to the Model S; I've had it happen in other cars (Hwy 401 in Ontario is notorious for this). The simple solution is to slow down a bit; this will reduce the cold wind blowing over the windshield, allowing the heater to raise its temperature enough to melt the ice. (Thanks Peter_M for the tip!)

    Finally, if your windows are fogging don't use the recirculate mode. Sure it will help keep the cabin warm, but it also means you're circulating moist air over the windows.

    One Last Thing

    Snow tires. Just do it.

    The Model S has excellent traction control and stability control - it responds very quickly and positively when the wheels start to slide. But you need to have good grip on the road, and that means good tires. It's amazing how confidence-inspiring the Model S handling is on snow and ice - but only if you put on a good set of winter tires.

    The Pirelli Sotozeros that Tesla sells aren't very good. Actually they're crap. They're "performance winter tires"; in my experience this use of the word "winter" really means "late fall/early spring". These tires are so bad in extremely slippery conditions that the car may not move at all. In fact the car doesn't even try to move... the traction control doesn't allow the wheels to turn and it just sits there. It's something of a basic requirement for driving that the wheels turn! In this situation just turn off TC and go very easy on the accelerator. But the better solution is to avoid the Pirellis altogether!

    I'm currently using Michelin XIce3 and they're a huge improvement. Many people on the forum swear by Nokian Hakkapeliitta R2, which is a great hard-core snow tire.

    Have Fun and Stay Safe!

    And don't forget to read my road tripping tips: The Rules of Model S Road Tripping - Blogs
     
  2. andyro

    andyro Member

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    Great tips Doug! Thanks for writing, just switched off range mode. One little thing I've done for when it's really cold and centre console hasn't booted yet, is set right scroll to turn on climate, temp scroll up and down, super handy, and that way the wife doesn't see me shut off climate for extending range a wee bit ;) I can attest to the statement that the Pirellis are crap. And yes, the car has encountered many situations where it refused to budge from a standing start, new snow tires on my next service! One question for you, why do you think tesla didn't insulate (thermal) the batteries for cold climates? Wouldn't it use far less energy to precondition that way, And even help keep cool in summer? What if like a chicken, tesla roosted on a bed of SM insulation when parked in my carport (using air susp to ride in and lower onto?)
     
  3. Doug_G

    Doug_G Lead Moderator

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    When I first got the car I had the scroll wheel set to control the fan, but the auto fan control was massively improved in a firmware update a long time ago.

    Ever since they fixed that I've had the scroll wheel set to temperature, like you. Very handy!

    Also, once the car is warmed up, turning off the climate control doesn't really save all that much energy. It only takes 1-2 kW. I prefer just to slow down a little and stay cozy. (I've had too many Roadster trips freezing my ass off despite wearing long johns. Model S is soooo much more comfortable in winter!)
     
  4. dasRad

    dasRad Member

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    I nursed our S85 through last winter on the Pirelli Sottozero IIs. It was embarrassing having to get a push to start it moving on a virtually flat surface covered with loose snow. With traction control on, the wheels wouldn't turn at all; with TC turned off, the rear tires just spun with even the lightest touch of the throttle.

    The Michelin XIce3 tires that I have this winter are a huge improvement. I no longer have to look for a flat parking spot from which I can push the vehicle to get it started. They do squirm on moderate to hard acceleration and braking (the Pirellis didn't), but I have a lot more confidence in them when it comes to getting going, and keeping a $100K vehicle out of the snowbank/ditch.
     
  5. ruby110

    ruby110 Member

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    Great info! Thanks.
     
  6. Xenoilphobe

    Xenoilphobe Active Member

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    Another comment for extreme cold weather driving - add a couple of ounces of 91% isopropyl alcohol to your windshield wiper fluid to help clear the ice/snow off the front window. In extreme cold it keeps the fluid from freezing and helps clear the window faster. I use this in all our vehicles.

    Thanks for the Range mode shut off tip - I wondered why my vehicle didn't warm as fast when on "shore power" in my insulated garage on the preheat mode!!!! - Fixing that tonight
     
  7. mknox

    mknox Well-Known Member

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    Great blog post, Doug and bang on with my observations as well. With my more typical longer range driving patterns I actually leave Range Mode OFF all winter, but have it ON all summer (mainly to keep the a/c compressor down to a dull roar).
     
  8. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Another of your excellent, information-packed blog posts, Doug; thanks for giving us somewhere to point newbies and the curious.

    By the way, I've got an S85 on Michelin Xi3s and a P85D on Hakka R2s. Both are excellent winter tires for snow and ice driving; I give the nod to the Hakkas for dry pavement grip and stiffer sidewalls, so that when the roads are clear you can access more of the car's available power before the tires get squidgy.
     
  9. andyro

    andyro Member

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    Stevezzzz - tx for the tire note. Will change my update to get the Hakka R2.
     
  10. MSEV

    MSEV Member

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    Thanks--very informative.
     
  11. JakeP

    JakeP S P4996 / X P6028

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    Fantastic blog post, Doug...you have "written the book" on cold-weather driving. And I remember your original tips from the winter of 2012/2013, when many of us were learning this for the very first time! I am very glad to see Tesla improving the vehicle's features and capabilities (with both software and hardware) to deal with cold weather over the past two years.
     
  12. kirstenoulton

    kirstenoulton Member

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    Great post and excellent organization of information. Thanks for sharing!
     
  13. neroden

    neroden Happy Model S Owner

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    (1) Clean out the wheel wells. Certain types of sticky snow will accumulate in the wheel wells and reduce your range DRASTICALLY. Get a stick and clean 'em out.

    This is the only tip Doug is missing. :)
     
  14. Doug_G

    Doug_G Lead Moderator

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    LOL neroden, I've never had it that bad! But a good tip!
     
  15. snooper77

    snooper77 Member

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    Thanks Doug!

    Do you have a source that confirms the 6 kW resistive heater and that there are indeed two heating modes?
     
  16. Doug_G

    Doug_G Lead Moderator

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    I've been told 6 kW for the pack heater by a Tesla employee. My own measurements have confirmed. You can get a rough idea of the power draw simply by looking at the dashboard gauge. More accurately I have measured the car's energy draw from a CS-90 charging station using an external meter. The CS-90 has more than enough power to fully handle both heaters at maximum draw. Using the remote app to preheat a thoroughly cold-soaked car at -20C, the car draws 11 kW. Running cabin heat only gives you half that. So it appears to be 5.5 kW for the cabin heater and 5.5 kW for the pack heater. Round numbers - 6 kW.

    As for the heat pump:

    1. At the Model S launch event in Fremont I asked an engineer and he said there is a heat pump. He didn't elaborate further.

    2. I have also looked at screen photos from the touchscreen HVAC diagnostic mode before it was locked down - very informative.

    3. Finally, from observation of the vehicle's operation: If you compare against the Roadster the Model S takes substantially more power when the car is cold, but once it warms up it takes substantially less power. Considering that the Roadster cabin is tiny and doesn't even get properly warm, the Model S has a lot more heating power for a lot less energy consumption. Thermodynamics tells you that all electric heaters have the exact same efficiency (exactly 100% - any losses come out as heat!); therefore the only way the Model S could be more efficient is if it uses a heat pump.

    4. Dual mode is necessary because the heat pump won't work well with a cold soaked car. Thus the resistive heaters.
     
  17. andyro

    andyro Member

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    Was able to get Michelin X-Ice3 tires from a cancelled sale - because Tesla will still only sell the Pirellis. IMO these really ought not to be the default Winter tire. Thanks for the rx Doug - and heater description. Wondering if periodic on/off heating is in fact less efficient than constant low temp (17.5-20) - as HP might operate better when matching heatloss, rather than ramping up to sudden heavy loads - I usually toggle on to de-fog windshield but keep seat heat to stay warm (my trips are often over 600km)... I don't trust 'range mode' to really help max my range, which is why I drive with sorels and a down vest, toque and mitts! (the canadian range extender kit)
     
  18. CanuckS#69

    CanuckS#69 Member

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    Toronto's Service Centres are now selling Hakka R2's, but at a pretty steep markup.

    I'm also on my third Canadian winter with my Model S and have clocked ~120k km so far. Everything that Doug has presented is spot on, but I'd add one additional tip for severe weather. When the roads are still a mess and the snow is still falling, keeping your speed up can be important. I've found that in extreme temperatures, 50kph isn't enough to produce enough motor heat to offset the pack heater. 70-80kph does the trick, but you don't always have that option if conditions are unsafe or your are restricted by the speed of traffic. If you are out in these sorts of conditions with no options, be aware that the pack heater will make a *serious* dent in your range even at low, efficient travel speeds due to being on the road longer with that 6kW monster eating battery for a longer period of time at low speed.

    One other note: I'm not sure if this is a recent firmware change or not, but while plugged in and fully charged, you now get the car's draw from shore power, which means that you can measure the heat, a/c, etc. draw directly from the car's instrument cluster.
     
  19. wycolo

    wycolo Active Member

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    If I had a garage I'd build up a platform with old foam pieces covering it. It would be sized to fit neatly under the battery to keep it warm overnight. Since my suspension is already Very High as I approach the 'ranch', I would just have to lower the car so the battery bottom surface squoushes into the foam rubber. Guiding boards would be needed to position the car. Also remember to raise car to max before driving off!!

    Bet this would make for great energy savings for winter commuters. [I'm not a commuter, though].

    No, the battery bottom cannot be permanently insulated since come a warm day the battery would overheat shutting down the car. [someone asked]

    Great blog Doug!
    --
     
  20. scottm

    scottm Member

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    Honest, officer... I'm keeping my speed up to prevent the car from freezing its batteries and coming to a halt. Maybe that will fly?

    Doug - you didn't talk about the snowflake symbol that also sometimes appears on the dash next to the battery. I think I've seen the snowflake without the accompanying blue marker on the battery pack... but not sure now, maybe they always come in conjunction with one another.

    JUST THINK of all these Tesla features Canadians get to try out and use ...that Floridians will never get the joy of experiencing.

    I will add a vote for Xice3, way to go... for Edmonton.

    AND GOOD TIP on turning OFF the traction control to get rolling. I never thought of that. There have been a couple times, on shear ice, where even the lightest touch on the pedal spins rears and car goes nowhere.. I thought I was going to be stranded on a flat road. That would have been embarrassing.

    I guess the other thing to try in similar situations is to turn Creep Mode ON. Maybe it has a lighter feather touch on the go pedal than a human for getting out of a slippery spot. Slight incline.

    Or the other thing might be, buy a D.
     

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