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Performance starting from cold

Discussion in 'Technical' started by ckessel, Aug 31, 2011.

  1. ckessel

    ckessel Active Member

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    Slight off topic, but related to performance. Do electric cars need to "warm up" like ICEs? If I get in the car in the morning and floor it down the first street, am I going to see the type of less than great performance I get out of an ICE in that situation?
     
  2. vfx

    vfx Well-Known Member

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    #2 vfx, Aug 31, 2011
    Last edited: Sep 3, 2011
    Best speeds are achieved with a warm battery. So the way you charge can affect your morning rush.
     
  3. TEG

    TEG TMC Moderator

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    #3 TEG, Aug 31, 2011
    Last edited: Aug 31, 2011
    Generally EVs are "ready to go" as soon as they are "booted up". Another great thing about them - great for short trips without waiting for warm-up.
    If it is really cold outside then the thing you may want is cabin warm-up (and EVs tend to have somewhat wimpy heaters), but some EVs (like the Leaf) let you pre-heat the cabin on a timer, or via iPhone directive.

    For ICE vehicles, part of the warm-up is getting the catalytic converters up to temp. Emissions tend to be worse when you first start them. So if you have a lot of short stop and go, an EV really shines compared to an ICE vehicle there.


    (Edit - now seeings VFX's response - the performance difference between a warm and cold battery tends to be relatively minor. For instance, a cold Roadster still performs quite well, I think. )
     
  4. Doug_G

    Doug_G Lead Moderator

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    No, unless:

    (a) you live in Northern climes and it is winter and
    (b) the car has been sitting unused and unplugged for a long time. In that case the battery pack could be cold-soaked below freezing.

    If the battery pack is below freezing, then you have some mild and temporary effects on the performance:

    1. Max power output is reduced a little. Unless you're trying to do 0-60 runs this is inconsequential.

    2. Regeneration is temporarily disabled, until the pack warms up.

    3. Efficiency is temporarily reduced. My car "loses" roughly 10 ideal km during the warm-up period, if the battery pack is below -10C.

    Once the pack warms up, which if it was very cold might take 10-15 minutes, everything goes completely back to normal. The slight loss in efficiency actually helps warm the pack up, as it is caused by slightly higher internal resistance in the cells.

    If the car was plugged in prior to use the battery pack is maintained a little above freezing. In that case none of the above applies.

    ICE cars have all the same issues, of course. In fact I'd say the Roadster handles cold way better than ICE cars do.
     
  5. vfx

    vfx Well-Known Member

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    Doug can you write a short paragraph on this? It's a common doubter/hater comment in blogs and forums.
     
  6. ckessel

    ckessel Active Member

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    #6 ckessel, Aug 31, 2011
    Last edited: Aug 31, 2011
    I said performance, but I meant to ask about health as well. Actually, I care more about that than a small drop in performance. ICEs, at least historically, needed time to warm up the oil and get it spread around and it wasn't good for the engine to go screaming down the road right away. Sounds like, from TEG and Doug, that's not the case with EVs.
     
  7. strider

    strider Active Member

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    Correct. I used to cringe every time my wife drove my Corvette as she would back out or the driveway and immediately tear off down the street. With the Roadster I don't care - there isn't anything that needs to "warm up".
     
  8. TEG

    TEG TMC Moderator

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    #8 TEG, Aug 31, 2011
    Last edited: Aug 31, 2011
    I guess it depends on just how cold you are talking about here...

    Does Cold Weather Injure Cell Phones? Abusive Lab Test - Popular Mechanics
    Can Cold Weather Damage My Laptop? | eHow.com
    Effect of freezing on Lithium Ion Batteries
     
  9. Doug_G

    Doug_G Lead Moderator

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    Here are some empirical results from last winter:

    Performance at -36C (-14.8F)

    As for a short paragraph... I'll try and write something up this evening.
     
  10. Doug_G

    Doug_G Lead Moderator

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    #10 Doug_G, Aug 31, 2011
    Last edited: Aug 31, 2011
    Okay, here goes. (Not sure if this is really the right thread, but it's where the question was asked.)

    In my experience, the Tesla Roadster handles cold better than internal combustion engine cars.

    Many ICE cars have trouble starting in the cold. Cold starts are very hard on the engine because it takes time for the extremely viscous lubrication to circulate. You have to start driving slowly before the engine has properly warmed up, otherwise you have a cold transmission connected to a hot engine - not good. The performance at first is very weak, and you can hear and feel the drive train struggle. The lubrication is extremely viscous, and thermodynamic efficiency is low because the combustion temperature is far from ideal. So until the car warms up the performance is very bad and the gas mileage is very poor. It takes quite a while for the engine heat to reach a point where the cabin heater will work, during which time the driver is cold and the windshield will tend to frost over.

    Compare that to a Tesla Roadster. Even if the car is completely cold-soaked, it switches on immediately, and you can drive away without any complaints from the drive train. Power deliver is smooth and quiet, and although there is slightly less power at first than normal, the car is still way faster than most ICE cars. Efficiency is lower until the pack warms up, which takes 10 to 15 minutes, and during that time you lose perhaps 10 km of total range. Yes, the cabin heater takes extra power from the battery, but the heat comes on almost immediately, and the total draw on the battery is modest. The heater takes less than 4 kW at full power, but it takes about 15 kW to move the car at highway speeds. Even under worst-case conditions you still have nearly 300 km of range, so the cold rarely has any impact on your driving.

    Yes, you can quote me.
     
  11. vfx

    vfx Well-Known Member

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    I already have!

    Thank you.

    So to bullet point it.
    • No oil to get thick in the engine or transmission.
    • Faster from the start.
    • Cabin heat and defrost is on in seconds
    What about handling? I have been telling people about the TC being faster that in ICE cars.
    Would be nice to have an average of gasoline miles lost on a cold start and run on an ICE motor to compare your 10Km loss to.
     
  12. Doug_G

    Doug_G Lead Moderator

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    Yes, the traction control is pretty awesome on snow. Last winter I took my car out in the snow to see how well it worked. We're talking AD07's on snow. It was amazing. Floor the pedal and it accelerated smoothly and without fuss. Let off the pedal and the TC kept the regen under control too.

    I think you'd need special equipment for that.
     
  13. cinergi

    cinergi Active Member

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    Not sure how many people reading this are aware of just how close ICE's come to not even starting when it's that cold outside. The RPM achieved while the starter is turning the motor is very slow, and as it approaches maximum compression, it almost sounds like that's where it'll stop turning over. It's quite disturbing. That's the result of reduced battery power as well as more friction (molasses for oil). I wonder if people are associating the poor battery performance of starting an ICE vehicle to how bad an electric "must be" ... I know I was thrilled that I could just pop into the car when it was -10F and go. And that I'd get good performance. My STi was TERRIBLE when the engine was cold. It wasn't good below operating temperature; it sort of sucked below 120F, pretty crappy at 60F, and nearly unusable at -10F (to the point where I wouldn't dare drive it without warming it up) -- largely because the engine (and in this case, the turbo) isn't tuned to operate at those temperatures.
     

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