How far can you go with EVs in Canada? A closer look at range, battery life - National | Globalnews.ca
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While 'range anxiety' used to be a factor in purchasing an electric vehicle years ago, consumers have less to worry about when it comes to how far their EV can go, experts say.

While ‘range anxiety’ used to be a factor in purchasing an electric vehicle years ago, consumers have less to worry about when it comes to how far their EV can go, experts say.

  • Thevenin@beehaw.org
    3·
    1 year ago

    Not sure I believe that. It takes less energy to keep a vehicle moving than it does to accelerate it. That’s not going to change whether it’s gas or electric.

    Merry Christmas, it’s physics time. When a vehicle is in motion, the forces the motors must fight are governed by the following equations: Ftotal= Fdrag + Frolling= 0.5ρv2CDA + NμR , where:

    • ρ = air density (kg/m^3)
    • v = velocity (m/s)
    • CD = coefficient of drag, defined by the shape of the car.
    • A = cross-sectional front-facing area of the car (m2)
    • μR = rolling resistance coefficient, which is calculated separately and depends mostly on tire pressure and surface quality. It changes a tiny bit with speed. In the example below, it’s 0.011.
    • N = Normal force, or weight of the car (N)

    If we take Ftotal and multiply it by the speed of the vehicle, we find the energy wasted per second, or the power needed to maintain that speed. Filling in the blanks for a Tesla Model 3 (because it’s easy to find the numbers) at 120kph (and ideal circumstances!), we find that Ftotal = 347.4 N + 196.4 N, and so Pwasted = 18.13 kJ/s or 18.13 kW. For a battery with 74 kWh usable, this translates to 489.8 km. Inside EVs tested their Model 3 at 112.6 kph and got 498.9 km, so this seems about right.

    Now let’s slow things down to 70 kph. Ftotal = 118.2 N + 196.4 N, and our range jumps to 846.7 km. That’s a lot, but hypermilers have gotten more in this particular vehicle. Now, I never said the 70kph example would have stops and starts, but since you brought them up, let’s see if we can recalculate with those in mind.

    The energy needed to bring a vehicle up to 70 kph is the kinetic energy adjusted up for a motor’s electrical efficiency, E = (1/.96)(1/2)mv2 = 358.4 kJ or 0.0996 kWh. The energy recuperated when using regen braking is the same, but adjusted down for the regen’s electrical efficiency, E = (0.7)(1/2)mv2 = 240.8 kJ or 0.0669 kWh. So a single stop-start cycle uses a net 0.0327 kWh. I’ll add one such 10-second start-stop cycle every 2 minutes (just spitballing), and recalculate for drag at the new speeds. We end up with an estimate of 733 km. This matches EV-database’s city range estimates in mild weather.

    Now, this may seem a bit startling, but the fact that EVs are more efficient in traffic than on the highway has been empirically measured. Personally, I can confirm that my range in my Clarity PHEV is about 50% longer at 45 mph than it is at 75 mph.