Why the BMW i3-REx

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:


Bob Wilson

 

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

 

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

 

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.

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:

• ~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

 

I'm using a new coding system, BimmerCode, and it works great:

• Power-on to PRO mode - works perfectly! This is the equivalent of "Normal" mode in the Prius.
• Set Time from GPS - not sure as I had just set the HH:MM when the car put in the mm/dd/yyyy. So far, time has remained perfect.
• Show tire pressure and temperature - this worked perfectly!
• Remove tank limit - set to what should be 2.4 gallons but my first fill-up was only 2.2 gallons. It could be technique but for now, I'm happy. This evening it showed a total range of 170 miles, gas and electric.

Bob Wilson

 

I ran the tank dry to measure how much gas I could add:

I was hoping for 2.4 gallons but this is close enough.

The effect is to increase the gas range:

Note that the range is calculated from the mi/kWh (rate of consumption), average speed, and a constant. In reality, we're looking at an additional ~16 miles:

• 72 mi - stock, 2014 BMW i3-REx (60 Ahr)
  • 86 mi - coded, 2014 BMW i3-REx (60 Ahr)
• 97 mi - stock, 2017 BMW i3-REx (94 Ahr)

Now this is a puzzle:

• 72 mi / 39 MPG ~= 1.85 gal
  • 86 mi / 39 MPG ~= 2.21 gal
• 97 mi / 35 MPG ~= 2.77 gal

This data suggests the tank in 94 Ahr BMW i3-REx might actually be physically larger the original.

Bob Wilson

 

Saturday I was thinking about driving 75 miles over to Tuscumbia for a Native American pow-wow. So which car to take:

• 25 mi EV, 600 mi gas - Prius Prime
• 72 mi EV, 92 mi gas - BMW i3-REx

First impression, BMW i3-REx:

• 25 mi EV + 125 mi gas :: Prius Prime
• 75 mi EV + 75 mi gas :: BMW i3-REx

So using a rule of thumb that 2 EV mi ~= 1 gas mi or each EV mi ~= 0.5 gas mi:

• (.5 * 25) + (1 * 125) ~= 130 cost units :: Prius Prime
• (.5 * 75) + (1 * 75) ~= 112.5 cost units :: BMW i3-REx is the cost winner

What this suggests is we may be able to calculate the 'break-even' distance between our 2014 BMW i3-REx and 2017 Prius Prime:

• 25 * ( (25 kWh/100 mi) * $0.10/kWh) + n * ( $2.50/gal / 54 MPG) :: Prius Prime cost per mile, after 25 mi
• 72 * ( (27 kWh/100 mi) * $0.10/kWh) + n * ( $2.75/gal / 39 MPG) :: BMW i3-REx cost per mile, after 72 mi

We have two equations with one unknown so we can solve for "n", the breakeven miles:

• $0.625 + (n * $0.0463) :: Prius Prime cost per mile, after 25 miles EV
• $1.944 + (n * $0.0705) :: BMW i3-REx cost per mile, after 72 miles EV
• $0.625 + (n * $0.0463) + ($0.625 + ((72-25) * $0.0463) = $1.944 + (n * $0.0705) :: cost after 72 miles EV
  • $0.625 + $0.625 + $2.176 + (n * $0.0463) = $1.944 + (n * $0.705)
  • $1.482 = n * ($0.705 - $0.463)
  • $1.482 = n * $0.242
  • 6.124 = n
• 72 + 6.124 = 78 miles :: break even miles AFTER 72 miles
• 150 miles total :: below this, use the BMW i3-REx. Above this, the Prius Prime

Curious as I thought it would be further.

Bob Wilson

 

Testing the REx to determine if there is an oil leak, I drove 102 miles including a brief stop at the Jack Daniels visitor center in Lynchburg TN:

In 6 minutes, 0.667 kWh which gives 6.67 kW per hour. Using 210VAC, 31A which is consistent with the maximum charge rate of the BMW i3-REx.

A 'Check Engine' light last month turned out to be low oil. Then after a recent rain, I noticed some 'oil sheen' on the water. So I'm running a series of REx tests to see if it is consuming oil and at what rate. Unfortunately, the BMW oil dipstick is a little tricky to read especially because the oil looks pristine. As for running the tank dry:

• 102 miles / 2.3 gal ~= 44.3 MPG (modest temps, using A/C, secondary roads)

Bob Wilson

 

From the training manual, 2.6L (2.7 quarts.) The level can change by 0.5L which explains the earlier, low oil condition. It doesn't take much to trigger the problem. In my case, the check engine light would come on when braking or taking a fast turn.

The oil sheen could have been a little 'spillage' when the service center corrected the low oil condition.

Bob Wilson

 

So today, 90 mile / 2.27 gal ~= 39.6 MPG.

Bob Wilson

 

Stuff learned today:


A close-up shows the oil level and the tissue comes close.

Then here are the SuperChargers at Athens:

Totally useless to my BMW i3-REx which does NOT persuade me to sell it and wait in line for a Model 3.

Curious self-parking that started adjacent to the trash bin. It passed the open space, a Fiat, and parked behind:


Bob Wilson

 

Late posting of a trip to view eclipse:

334 miles eclipse trip - a day-trip using BimmerCode tank expansion, three fill-ups, 2.3 gallons, and the 75% REx option. I did not take the spare can as the goal was to measure the usable gas capacity. I also changed the default driving mode to use "Pro" with softer acceleration and slightly moderated A/C to extend the range.

Bob Wilson

 

Not yet but it is a little tricky because the front and rear tires are different tread widths. I can mount a front tire on the rear but not vice versa.

My current plan is to get 2", spare tire carrier(s). One for each car and carry the spare with appropriate locks, on the rear and relocating the license plate. It is not a trivial problem because the plates need a light at night.

I keep the Prime spare behind the passenger seat for now.

Bob Wilson