Why the BMW i3-REx

Discussion in 'EV (Electric Vehicle) Discussion' started by bwilson4web, May 15, 2016.

  1. bwilson4web

    bwilson4web 03 and 10 Prius

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    So we have both a 2017 Prius Prime and 2014 BMW i3-REx . . . which one to drive today:
    • BMW i3-REx - best urban car, a pocket rocket with a high seating and excellent view. The power to weight ratio means point and scoot and the short wheel base parks easy. It has acceptable cross-country capability but stay near interstates especially at night as it is 80 miles per segment and carry a 1 gallon spare can.
    • Prius Prime Plus - best cross country car, smooth, excellent suspension and outstanding highway MPG. Visibility is much improved over our Gen-3 and the dynamic cruise control is great. Around town, know your charging locations and shop at nearby stores. The traction battery charges ~40% or 10 miles per hour and has no fast charging. In town, it drives like a tuned-up Prius, more than adequate.
    Bob Wilson
     
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  2. bwilson4web

    bwilson4web 03 and 10 Prius

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    Source: BMW i3 plug-in hybrid recall to fix fuel-vapor problem, fire concerns

    BMW is recalling more than 19,000 i3 REx extended-range electric cars due to concerns over the potential for fires to be started by fuel vapors.

    The REx uses a small gasoline engine to charge its battery pack, offering a longer range than the all-electric i3 when both gasoline and electric power are used.

    According to the National Highway Traffic Safety Administration, the i3's fuel-tank vent line may rub against the ribbed wire protection sleeve of the battery positive cable.
    . . .

    I am so glad we have a 2017 Prius Prime that replaced our Gen-3 Prius.

    Bob Wilson
     
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  3. bwilson4web

    bwilson4web 03 and 10 Prius

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  4. bwilson4web

    bwilson4web 03 and 10 Prius

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    HOME TO WORK

    Preconditioning, nice cabin and 100% SOC. Got to cross-town intersection and had forgotten work badge. Added 3 miles to commute and brought SOC to 87% instead of 91%.

    Work to Nashville

    About 8-9 miles, the SOC reached 75% and I turned on the REx. In Ardmore, 20-25 miles at the Interstate, topped off gas tank, grabbed a burger and unsweetened tea and on the 70 mph I-65.

    Now 70 mph is the REx output energy output. I had a 15 mph tailwind but had to climb the Piedmont. SOC decayed from 75% to 72% and stayed there.

    Followed a 70 mph truck to Nashville but ran out of gas 6 miles short with 70 miles EV range in battery. Horrors! I continued and arrived actually an hour early.

    Sweet Home

    Turns out ChargePoint had put in a new, four hose charger three blocks away. At $0.84/hr, reasonable. The a block and a half away, a new Japanese style restaurant and sushi bar. Just the thing to eat a brunch before heading to a gas station and home.

    Expenses
    • $1.19 - top off tank in Ardmore
    • $1.35 (7.161 kWh) - charge in Nashville, $0.18/kWh
    • $4.98 (2.007 gal) - fill-up tank in Nashville ($2.48/gal)
    • $0.72 (7.161 kWh) - charge in Huntsville residential rate, $0.10/kWh
    • $4.50 (2 gallons ) - fill-up local Huntsville fuel, $2/gal Reg, $2.25/gal Premium
    • $12.74 - expected gas and electricity
    • 234 miles - HSV->Nashville->HSV
    • $0.054 / mile
    With the expense per mile, we can reverse calculate the equivalent expense using Huntsville prices:
    • $2/gal Reg / $0.054/mile ~= 36.7 MPG (regular)
    • $2.25/gal Prem / $0.054/mile ~= 41.4 MPG (premium)
    Ouch, I was not expecting this but I did have fun driving the Bimmer. Given the measured MPG at 70 mph is 38 MPG, this is about right. I did not dilute enough of the trip energy with electricity, the cheaper fuel.

    The USA default is to turn on the REx at 6% but some have found there is not enough energy to handle highway loads without limiting performance during the engine warm-up. If I wait until the SOC is ~12-18% instead of starting at 75%, then more of the gas, the expensive fuel, will be preserved, left in the tank. FYI, the SOC was ~40% when I parked.

    The lesson learned is if you're blending electric and gas on a given trip, maximize the electrical usage and preserve the gas. This is not a trivial problem because loss of electrical and gas energy can be unpleasant. Time to carry a spare gallon for future runs.

    Bob Wilson
     
    #364 bwilson4web, Mar 6, 2017
    Last edited: Mar 6, 2017
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  5. bwilson4web

    bwilson4web 03 and 10 Prius

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    A little math fun:
    • cost_per_mile = cost_per_gallon / miles_per_gallon
    • EV_cost_per_mile = cost_per_kWh / miles_per_kWh
    So we can the calculate the trip cost:
    • n%_gas_miles
    • 1 - n%_gas_miles
    Huntsville:
    model gas_price kWh_price MPG mi/kWh $gas/mi $kWh/mi
    1 BMW i3-REx $2.35 $0.11 39 3.4 $0.0603 $0.0324
    2 Prius Prime $1.97 $0.11 54 4.0 $0.0365 $0.0275


    Nashville:
    model gas_price kWh_price MPG mi/kWh $gas/mi $kWh/mi
    1 BMW i3-REx $2.25 $0.18 39 3.4 $0.0577 $0.0529
    2 Prius Prime $1.92 $0.18 54 4.0 $0.0356 $0.0450

    ChargePoint $0.85 for 6.6 kWh = $0.18/kWh
    Gas prices from gasbuddy.com​

    Well I wasn't expecting this:
    • BMW i3-REx is more efficient EV regardless of Huntsville or Nashville rates, slightly.
    • Prius Prime is more efficient EV in Huntsville but somewhat cheaper on gas in Nashville
    This suggests we should be able to make a table of gas and electric costs that defines parity for both cars. Then select the motive fuel/energy to minimize the cost per mile. It should be linear relationship for each vehicle.

    Bob Wilson
     
    #365 bwilson4web, Mar 7, 2017
    Last edited: Mar 8, 2017
  6. bwilson4web

    bwilson4web 03 and 10 Prius

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    Prime Plus
    Got a nice e-mail from ChargePoint:

    Hi Robert,
    Just a heads up, your Toyota Complimentary Charging balance of $98.65 expires in 60 days. Any remaining Toyota Complimentary Charging balance will disappear at that time, and has no cash value. See full terms and conditions here.
    Don't worry, you can keep using your ChargePoint card or mobile app to charge your Prius Prime after your balance expires.
    We hope you're having fun driving in EV mode.
    Charge on,
    Team ChargePoint

    I charged the BMW i3-REx in Nashville.

    Bob Wilson

     
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  7. bisco

    bisco cookie crumbler

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    very nice of them to send out reminders.
     
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  8. bwilson4web

    bwilson4web 03 and 10 Prius

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    I have to admit, driving the BMW i3-REx around town is a blast.

    Bob Wilson
     
  9. hill

    hill High Fiber Member

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    To blow through that $98 credit on our employee Chargepoint EVSE's - costing 28ยข/kWh, all i'd have to do is drive <20miles/day & i'd have all that $$ spent ... you can do it - easy peazy !

    .