Why the BMW i3-REx

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

  1. bwilson4web

    bwilson4web i3 and Prime

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    Prime Plus
    One of the first BMW i3-REx in the USA was in an accident:
    Tom Moloughney (see Facebook)

    A lady "was looking at her radio and didn't realize the light had turned red" and t-boned me on the passenger side. I don't have final word from the insurance company but the CFRP frame has a hairline crack and there's about $10,000 worth of damage besides the CFRP work so it's likely a total loss.

    The good news is how well the car held up. It was a pretty severe hit, as she was going about 45 mph and didn't even touch the brakes. My car was pushed about 15 ft sideways and then did a 180. I'm very lucky that a car on the other side of the road didn't plow into me also because I ended up in the opposite lane of traffic. I'm mostly OK, just sore as heck.

    There are no good accidents but in this case, the car and its carbon fiber body took the worst of the damage. It was pretty severe:
    [​IMG]

    Bob Wilson
     
  2. bwilson4web

    bwilson4web i3 and Prime

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    When giving a test drive, make sure no turning is involved in a maximum acceleration test. A nice lady driver got into 'driver induced oscillation' doing a maximum acceleration merge onto an Interstate. Once she backed off on the accelerator, everything was fine.

    Lesson learned by me,
    Bob Wilson
     
  3. hill

    hill High Fiber Member

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    Bob,
    doing a Google search I see there haven't been any fatalities in the i3 (as far as I can tell). I found a video / rear-end collision resulting in a battery fire & that's about it. True, there hasn't been 100's of millions of miles like Tesla has logged (& many of those owners' idiot behavior brought folly upon their self) , but still ... it's a significance testimony to BMW & the i3.
    .
     
  4. bwilson4web

    bwilson4web i3 and Prime

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    Prime Plus
    There could be multiple factors:
    • High rates of lease - both mileage limits and a desire to preserve end of lease value.
    • Not cheap - more successful people could be more attentive drivers.
    • Carbon fiber has excellent crash performance - protecting occupants.
    Someone asked me to choose between Prime and i3 but I am driving the i3 today ... it runs the A/C and it is a heat condition black day. The car, cabin, and battery is being cooled as I thumb type at high noon.

    Bob Wilson
     
  5. bwilson4web

    bwilson4web i3 and Prime

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    Earlier this week, the car was parked in an alley in the sun, +90F, with the windows up. While I had lunch, the car charged as expected and I noticed the taper down. So I paid my bill, checked the charge and noticed it had just dropped to 0 amps.
    [​IMG]
    I had to do some shopping at the corner grocery store and remember selecting the first option, "Activate Now" to cool the cabin. When I unplugged the car, the 'blue' light was blinking and drove home. It was later when I noticed the 'cool down' profile.

    The chart shows the cool down ramped up to ~4.5 kW and then down to ~1.5 kW which it held until I unplugged. The high initial rate suggests it might have been trying to cool the battery but I'm not sure.
    Pure speculation on my part but I wonder if "Activate Now" may follow a cool-down protocol:
    • Check cabin to start either cooling or heating, in this case, cooling.
    • Check battery temperature, if too warm, start cooling.
    • As battery temperature comes down, reduce cooling.
    • Continue cabin cooling as needed based on temperature measurements.

    Summer in Alabama, I can repeat the lunch test only next time use the "Set Departure Time" instead. If the cool-down profile changes, we'll have data to share. Being retired, I can set my own schedule but I'm open to suggestions to improve the test.

    Going from home to Propst:
    • 6.7 miles - leave at 10:40 AM, ~1.5 kWh @4.5 mi/kWh
    • Plug-in at 11:00 AM - when my favorite restaurant opens
    • Lunch - wait for charge current to drop to 0 A, should take ~20-30 minutes
    • Wait 15 minutes
    • Schedule departure time one hour out (to see if it starts right away or waits)
    • Hang until the EVSE shows 0A or 2:00 PM, last call for lunch (bring a good book)

    Bob Wilson
    . . .
    Fri Jul 21, 2017 5:37 pm



    So I ran the test today and got the following:
    [​IMG]
    • ~11:10 AM - plugged in the car after driving 6.5 miles in 16 minutes. At 88F (31C) on the driveway, it was 92F (33C) when I parked in the alley to plug-in. I then put in our prescription refills and went to lunch.
    • ~11:40 AM - I noticed charging had stopped so I scheduled a departure time of 12:45 PM
    • ~11:45 AM - within a minute of sending the departure time, there was a five minute charging session, 1.72-1.42 kW. I've seen these short, charge bursts in the past so I suspect is it not related to getting the departure time message.
    • ~12:18 PM - charging bursts up to a peak of 5.8 kW and in 10 minutes down to 1.8 kW
    • ~12:45 PM - down to 1.4 kW while I was getting our prescriptions
    • ~12:50 PM - down to 1.3 kW when I entered the car, I could hear the A/C working and the interior was nice.

    I loaded the chart into a spreadsheet and digitized the curves relative to 00:00:00 (hh:mm:ss):
    Time,kW
    00:00:00,0.00
    00:02:40,0.00
    00:03:15,6.48
    00:12:30,6.40
    00:16:30,3.50
    00:21:00,1.85
    00:25:00,1.40
    00:30:00,0.85
    00:36:15,0.60
    00:36:30,0.00
    00:45:00,0.00
    00:45:25,1.72
    00:50:00,1.42
    00:50:15,0.00
    01:05:00,0.00
    01:18:00,0.00
    01:18:20,5.80
    01:21:00,3.10
    01:27:00,2.30
    01:27:15,1.80
    01:38:00,1.60
    01:40:00,1.55
    01:45:00,1.40
    01:50:00,1.30
    01:50:15,0.00
    02:00:00,0.00

    Initial Thoughts

    "Activate Now" - on Wednesday, there was not enough time to let the battery reach a state where the second charge pulse could occur independently. So the triangular shaped charge probably is a combination of battery thermal management followed by a decay to the 1.4-1.8 kW range when the cabin cooling becomes a steady state load.

    "Set departure time" - by having a one hour delay, the initial battery charge and probably thermal delayed, final charge, occurs letting the car achieve a steady state while parked. Then based upon the set time, about 20 minutes before departure, there is jump to 5.8 kW that is probably a battery cooling, initial topping charge, and possibly the cabin (not observed.) After 10 minutes there is step down to 1.8 kW that at the scheduled departure time is 1.4 kW and five minutes later, 1.3 kW.

    I suspect the longer preconditioning lead times, ~3 hrs, occur in cold weather when the battery has to be warmed up. A cold-soaked battery probably needs the longer time to reach an optimum operating temperature.

    In contrast, these hot weather tests did not include a heat-soak. I had to drive to the recording EVSE, ~15 minutes giving an initial, operating cool-down. I started in the shade with external temperatures of ~90F (32C) and then parking in a sun lit, alley 100F (37C). There was not enough time to properly heat the battery to ambient temperature.

    That is what the data suggests to me given we're limited to just the EVSE charging data.

    Bob Wilson