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Kwh / WH/mi ??

Discussion in 'Model 3: Battery & Charging' started by LSE47, Jun 16, 2018.

  1. LSE47

    LSE47 Member

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    The odometer cards shows kWh and Wh/mi. what are these measuring exactly, and how should i think about them? is it better to have higher or lower results?
     
  2. Big Earl

    Big Earl Supporting Member

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    A kWh, or kiloWatt-hour is a measure of energy. 33.7 kWh is the equivalent energy in one gallon of gasoline. 250 Watt-hours per mile translates into 4 miles per kWh. Tesla uses the former metric, while most other EVs use the latter. Lower Wh/mi means you're driving more efficiently, while higher miles per kWh is more efficient.

    For charging, if you charge at a rate of 10 kW (10,000 watts) for 5 hours, you will have added 50 kWh to your battery.
     
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  3. DSaul

    DSaul Member

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    KWh = 1000Wh, energy measure.
    Wh/mi: How much energy you use every mile.
    KW is power (at that moment) vs KWh is energy (power during period of 1h). Car using or charging at 10KW of power for 2hours means using or charging 20KWh of energy.
    Battery on the 75D for example, can store 75 KWh or 75,000 Wh of energy.
    If you divide battery capacity by the Wh/mi, you will get the range. 75000Wh / 300Wh/mi = 250 miles
     
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  4. Candleflame

    Candleflame Member

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    its the same as L/100km divided by 100. Not sure why they don't use that given that people are used to this measure.

    The lower, the better.
     
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  5. ewoodrick

    ewoodrick Member

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    Lower is better (less energy per mile) 250 or less is good.

    If you want a more conventional reading, use 1,000. Wh/mi and you will get miles/kWHr (similar to miles per gallon). 4 or more is good and the higher the better.

    I was going over the Smoky Mountains today. I topped out at about 800 Wh/mi, which is terrible
    But going downhill, I got better than -200 Wh/mi over a 10 mile distance. (which means I'm charging the battery)
     
  6. LSE47

    LSE47 Member

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    got it thanks all. my daily commute is almost all highway and traffic usually moves 70 -80 mph. Wh/m is in 300 - 325 range. will take a few trips at 65 and see how the Wh/m changes.
     
  7. CTreast

    CTreast Member

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    I'm getting incredibly good performance but I also strive for it. After my first week of driving like a bat out of hell that is ;)
     

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  8. DannyHamilton

    DannyHamilton Member

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    Picked up the car a bit more than 5 weeks ago (May 18th). Since then, I've driven over 3,600 miles. I've got an average of 200 Wh/mi over that distance:

    IMG_1396.JPG
     
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  9. sperkin

    sperkin Member

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    #9 sperkin, Jun 24, 2018
    Last edited: Jun 24, 2018
    I'm around 188 to 190 mostly on AP. Usually can around 157 in a trip but like to do a few bursts here and there. This car is very efficient at speed.

    18" with aero caps off.

    20180624_220050.jpg
     
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  10. Fusion

    Fusion Member

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    How fast are you guys driving getting 180-190?? 40-50mph i would guess.
     
  11. DannyHamilton

    DannyHamilton Member

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    Prior to the Model 3, I had a Volt for 2.5 years. Before that I had a Prius for 10 years. The MPG feedback on those vehicles seems to have trained me to be more efficient in general. I don't think it's just my speed. It's a lot of small things that all add up.

    Aeros? Yes.
    Garage? Yes at home. No at the office.
    Preconditioning while plugged in before most drives? Yes (but not always).
    Chill mode? Yes (but I'll switch it to Standard when letting someone try driving it or I have a passenger in the car for their first time)
    EAP? Yes.

    I also keep the battery as close to half way charged as I reasonably can. As an example, I have access to a 24 amp Level 2 charger at work. It is a 40 mile commute each way. I leave work with 40 miles above half: (310 / 2) + 40 = 195 miles. I arrive home at a bit more than half full since I'm more efficient than the calculated range. A few miles of range are lost overnight while the car sleeps. I leave for work with anywhere from a few miles less than half to a few miles more than half. When I get to work I'm 30 to 40 miles below half. Then I plug in and charge back up to 40 miles above half again.

    The weather here in the Chicagoland area has been pleasant enough in the mornings and evenings (when I do most of my driving) that I can usually open all four windows between a 1/4 inch and 1/2 inch and remain comfortable without needing to run the A/C (although there were a few days when I decided the A/C was necessary to keep myself or my passengers comfortable).

    90% or more of my driving is expressway. I get in the right-hand hand lane. I set the TACC speed at the exact speed limit. I set my following distance at the maximum (7). If I encounter a slower vehicle in my lane, I just stay behind them and allow the TACC to match their speed. I don't change lanes and go around them. I watch ahead when approaching on-ramps. If there is a vehicle on the ramp I adjust the TACC down by 1 or 2 MPH to allow a gap for them to easily merge in without me needing to accelerate or decelerate hard to get out of their way. Once they've merged I adjust the TACC back up to the speed limit. If I see traffic slowing ahead and/or brake lights ahead, I start reducing my speed in 1 or 2 MPH increments before I get there. By the time the TACC needs to slow me down I'm already only a few MPH faster than traffic is moving (or already at 18 MPH if traffic is stopped).

    I leave a larger gap than most people do between myself and the car in front of me when off the expressway as well allowing a more gradual braking for me when they stop (and often allowing me to avoid coming to a stop before they start up again).

    The land here is rather flat, my travel is largely North and South while prevailing winds tend to be from the West to East so it is rare that I need to deal with much of a headwind. Heavy rain will result in a significant drop in efficiency for a trip, but most of our rain this season has been when I'm not driving (mid-day or overnight). About 8 miles of any trip to or from home has a speed limit of 70 MPH. Then the limit drops to 65 MPH for the next 12 miles or so. After that I'm close enough to the city that most of the expressways have a limit of 55 MPH. Most of my trips are 40 miles twice a day during the week, and 60 miles twice a day on the weekends. I'm often in heavy traffic so I (along with everyone else on the road) am stuck going significantly slower than the speed limit for long stretches of the drive, especially in the areas where the speed limit has already dropped to 55 MPH.

    In terms of efficiency, regen braking is better than friction braking, but NOT braking is better than regen braking. The OPTIMAL efficiency if there were no other cars on the roads, and you could perfectly time your stops would be to accelerate slowly up to your necessary travel speed, maintain exactly that speed for the duration of your drive, and then coast without regen (effectively in neutral) back down to a stop exactly at your destination. Unfortunately, the real world gets in the way, and we often need to accelerate hard enough to get out of the way, travel at speeds fast enough not to inhibit the traffic around us, and stop faster than coasting would allow. In these real world conditions, efficiency can be maximized by accelerating no harder than necessary, driving no faster than necessary, and starting any stops as soon as possible allowing the minimum amount of regen that will stop the vehicle without needing to use the friction brakes and increasing the probability that the obstruction will move before we need to come to a full stop.
     
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  12. sperkin

    sperkin Member

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    You have to drive a little harder than an ICE car trying to save gas because the motor needs regen to get energy back. I tried driving with as little black bar as possible but that means I hardly get any green bars when slowing down in traffic. What AP does is it get 1/4 to 1/2 black bar when accelerating and then jumps off the accelerator to get 1/4 to 1/2 green bars to regen. It's a rougher ride than I'm used to but it's very efficient. I still haven't been able to beat AP and since AP reduces stress a lot I just let it drive and I watch out the window instead of trying to lower the energy usage now.

    I have a feeling AWD will be even more efficient since my loaner S had AWD and once it hits 75/80 mph the wh/m drops.
     
  13. sperkin

    sperkin Member

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    My experience has been different. Without using regen to stop my wh/m doesn't drop. For me, I have to keep the car in green (regen) as long as possible before I come to a stop. When I exit a freeway, I hold the accelerator down a little so the car is in regen all the way to the end and then I left off once I reach 5mph. Coasting down like it's neutral doesn't seem to recover any energy for me.
     
  14. DannyHamilton

    DannyHamilton Member

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    The point isn't to "recover energy." The point is not to have converted the unneeded energy from chemical (in the battery) to electrical (in the wires, controller, and motor) to kinetic (in the motion of the car) in the first place. The longer you can keep that energy in the battery and not use it, the less times you'll experience losses from friction and energy conversion. Every one of those conversion steps results in losses. Then when you "recover" it, you need to convert it back from kinetic, to electrical, to chemical in order to store it, and back from chemical to electrical to kinetic when you go to re-use it. That's a lot of losses.

    By starting the stop earlier, you stop pulling the energy out of the battery sooner (and start putting any extra back in to the battery sooner).
     
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  15. Rocky_H

    Rocky_H Active Member

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    Reminds me of the car review site that talked in their review of an electric car about trying to extend the range by speeding up really hard so they could regen really hard to "create energy". o_O They were actually serious.
     
  16. ElectricCanuck

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    Am I correct in thinking that figuring out charging cost from empty to full is Cost per KWh * Size of Battery in KW?

    So, in Ontario, I pay $0.065/KWh off peak -- so charging from empty to full (75KW) costs $4.80?
     
  17. CO2CLEAN

    CO2CLEAN Olivier Willemsen

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    Yes, but there is also a loss when charging. This can amount to ~10%.
     
  18. ElectricCanuck

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    Good to know - thanks!
     
  19. Oldschool496

    Oldschool496 Member

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    #19 Oldschool496, Jul 6, 2018
    Last edited: Jul 6, 2018
    If your in hilly area, which I am not, I understand the regen. is great. Really day to day here and there regen. is hardly something you should be measuring or be depending on any sort of distance down the road from it. Its free brakes with some upside in a very small way to range of any kind.

    On a trip. MS75D. Rule of thumb, never travel faster then you can afford in time at the charger. It makes no sense to go faster then you need and wait longer perhaps or stop more.

    77 MPH= Aprox. 325 Watt HRS/mile with AC on daytime and sometimes wipers, a little Defrost here and there 225 miles of actual range.

    225x325 = 73KW battery Basically getting three miles per kWh of battery at 75-80

    If I go slower or I am thrifty here and there, then my range goes up obviously. On a trip you may be asked to go slower early on after a charge to make it to next charger. Less frequent these days/more chargers available.

    Never get to 225 because I am hopefully stopping and charging. Keep a steady pedal no pumping.

    Yes, from what I can tell the Dual Motor is very efficient between 75-80. I have had 6 loaners, the first was Signature RWD 85+, while it was a gorgeous car, it was the worst, ate energy.

    The rest have all been P85Ds and most act just like 75Ds from a range perspective. Almost exact with their own degradation from age if you keep your foot out of it on a trip. Otherwise, I have my foot in it around town more then is safe.

    These days around here anyway the new speed is 80-95 for 1/3 of the drivers. Pump in some more gas/$ and go like hell again.
     
  20. adaptabl

    adaptabl Member

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    There is also transportation fee's on every KWH of about 6 cents per KWH to add to that cost. That brings the cost to a little more than $9.00
     

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