Second BMW i3-REx

[bwilson4web]

My first, 2014 BMW i3-REx left with the former wife after the no-fault divorce. With only an out of warranty 2019 Tesla Model 3 Std Rng Plus, I needed a backup to slow battery degradation, 9-10% with 120,000 mi and $15k to replace. A retired engineer, I prefer 'self maintenance' but you need a second car for the multi-day tasks, missing tools, and needed parts.

I found a 2017 BMW i3-REx, 55,000 mi, $15,000 at a Florida Toyota dealer. It was detailed fine with new rubber but they had no portable charger (yes, EVSE) so they gave me a test drive on just the REx!

I field tested the battery by having their service department plug in their 'unused' J1772 for exactly 2 hours and found it had ~27 kWh of the original 28 kWh.

Field testing is starting with a low SOC, plug in a charger that reports the SOC or remember 6.2 kW = 30A @208 VAC (commercial). So in 2 hours of charging at 6.2 kW:

​

12.4 kWh = 2 h * 6.2 kW :: charge added by clock​

45% = 45% - 0% :: increased SOC​

27 kWh ~= 12.4 kWh / 45 % :: field tested battery capacity​

Field testing works for any EV. But since the portable EVSE was missing as well as the tire kit, I got $500 off the purchase. The dealer and I left thinking we'd really pulled a fast one on the other.

Driving the 835 miles home, it cost ~$85 in mid-grade gas. Subsequent benchmarks showed: a 106 mi EV range at 65 mph (my EPA metric speed is 63 mph), and; 88 mi gas range, single tank. In contrast, the Tesla inspection trip cost $66 in SuperCharger fees.

This morning, the BMW i3-REx is fully charged with over 66,000 mi. The recent cold snap has reduced the indicated range to ~112-135 mi range. The REx has only run only for the periodic, range extender self-maintenance mode.

So my life:

• Urban pocket rocket - the BMW i3-REx has a short wheel base, BMW handling, and handles EV trips to regional towns. Dumb cruise control, it is a driver's car around town but tends to 'rocking horse' on the Interstate highways.
• Highway Zen Master - the Tesla long wheel base and suspension is comfortable on the highway with Autopilot and Full Self Driving handling the chauffeur duties. Best of all, the number of battery aging charge cycles has gone down by 1/3d.

Bob Wilson

 

[alohart]

My first, 2014 BMW i3-REx left with the former wife after the no-fault divorce.

So sorry to learn of your divorce, Bob. I know that you were very conscientious in meeting your wife's needs with your cars.

Field testing is starting with a low SOC, plug in a charger that reports the SOC or remember 6.2 kW = 30A @208 VAC (commercial). So in 2 hours of charging at 6.2 kW:

​

12.4 kWh = 2 h * 6.2 kW :: charge added by clock​

45% = 45% - 0% :: increased SOC​

27 kWh ~= 12.4 kWh / 45 % :: field tested battery capacity​

You seem to have ignored the charging energy converted to heat and to powering the HV system that is on during active charging rather than used to increase the battery pack's charge level. The mi3 app reports that my 16 A @ 208 V home charging efficiency is 88% (our apartment complex has 3-phase commercial power). The Idaho National Laboratory reported 30 A @ 208 V charging efficiency to be 93.4%. Including this efficiency would decrease the usable capacity of your battery pack to about ~26 kWh.

However, as shown in the Samsung SDI 94 Ah battery cell spec sheet, the gross capacity depends on temperature and charging or discharging power with the usable capacity controlled by the BMS in ways that are probably not documented, so determining an exact usable capacity under all conditions is probably not possible. The gross capacity would be 33.1 kWh for a 96-cell i3 battery pack when discharged at 1/3 C (11 kW) @ 25 ºC. The life expectancy based on either age or charge-discharge cycle count is impressive. 94 Ah battery cells seem to be very resistant to significant degradation, especially compared with some 60 Ah battery cells.

 

[bwilson4web]

You are correct. I should have applied a charging efficiency factor but I didn't know what to use.

Once I got home, I did controlled benchmarks:

• 106 mi EV range
• 88 mi gas range

<GRINS>

Thanks,
Bob Wilson

 

[JohnnyCakes]

Kinda off topic, but are you the famous Bob Wilson from "how far can my Prius actually go when the car says zero?" If so, many thanks for your work on that. My other car is a Prius camper and you've removed all range anxiety.

 

[JohnnyCakes]

@bwilson4web
…or maybe not. Lol