Neil
Posts: 45
Joined: Sat Sep 06, 2014 10:11 am
Location: Davis, CA USA

Range reduction in cold weather

Wed Feb 20, 2019 10:43 pm

In the 4+ years I've had my i3 Rex, I seemed to hear about how good the battery management system is on the i3, yet according to this recent article the i3 was the worst of the 5 tested vehicles which were mostly 2018 models.

https://www.powerelectronics.com/automo ... 89ae96d230

From the article:
The BMW i3 was most sensitive to temperature change in both hot and cold conditions, losing 50% and 21% of range in cold and hot conditions, respectively. The Nissan Leaf was the most temperature-resistant, losing 31% and 11% of range in cold and hot conditions, respectively.
I certainly didn't expect these results. Have the other car makers surpassed BMW in this regard? Any other explanations, etc. out there?

Oleksiy
Posts: 93
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: Range reduction in cold weather

Thu Feb 21, 2019 2:25 am

I'm still in my first year of i3 (2015 BEV) ownership, and I'm very pleased with its performance in various weather conditions, having researched this issue before purchase. I keep daily logs of my trips, so just throwing in some stats from my monthly pivot spreadsheet here (all metrics converted to imperial for convenience):

month * mileage * average efficiency * average speed * average ambient temp * average estimated range based on miles driven and DoD * battery capacity, trip comp * battery capacity, Batt.Kapa

Jun 2018 * 1,349 miles * 5.34 miles/kWh * 25 mph * 73.3 F * 99 miles * 18.6 kWh * 18.1 kWh
Jul 2018 * 1,516 miles * 5.36 miles/kWh * 29 mph * 72.1 F * 97 miles * 18.1 kWh * 18.0 kWh
Aug 2018 * 985 miles * 5.39 miles/kWh * 26 mph * 75.7 F * 97 miles * 18.0 kWh * 17.9 kWh
Sep 2018 * 1,377 miles * 5.17 miles/kWh * 28 mph * 62.6 F * 92 miles * 17.8 kWh * 17.8 kWh
Oct 2018 * 1,367 miles * 4.93 miles/kWh * 28 mph * 51.9 F * 87 miles * 17.6 kWh * 17.6 kWh
Nov 2018 * 1,053 miles * 4.12 miles/kWh * 27 mph * 33.1 F * 71 miles * 17.2 kWh * 17.5 kWh
Dec 2018 * 875 miles * 3.89 miles/kWh * 25 mph * 29.3 F * 66 miles * 16.9 kWh * 17.4 kWh
Jan 2019 * 1,513 miles * 3.68 miles/kWh * 24 mph * 22.5 F * 62 miles * 16.7 kWh * 17.2 kWh
Feb 2019 * 730 miles * 3.95 miles/kWh * 27 mph * 32.6 F * 67 miles * 16.9 kWh * 16.9 kWh

My use pattern is as follows:
- I drive in EcoPro
- I use AC and climate in Auto, one-two fan bars in summer and Sep, temp is set on 72F
- Any colder whether I use climate in Auto, one-two fan bars, temp is set on 66F.

As you can see, in terms of efficiency, the worst month (Jan) is 68% of the best one (Aug). This effect is driven by temperature - the higher the ambient temperature - the better the efficiency. This difference is partially explained by falling battery capacity (lost in winter either because of lower ambient temperature or normal degradation, or both) - it dropped by 7% or 4% in Jan depending on the estimate used.

The range impact was more severe - Jan estimated range is 64% of the Aug estimate.

I read a lot of EV forums before purchase, mostly Leaf, Kia Soul and i3. My preliminary assumption of summer-winter difference was 60% as a result. So my i3 has outperformed the expectations.

CanisLupus
Posts: 113
Joined: Thu Sep 15, 2016 10:48 pm

Re: Range reduction in cold weather

Thu Feb 21, 2019 9:21 am

This is what I want to suggest .

I think that , perhaps , only the voltage of the battery is being used to calculate the SOC .

It seems clear , however , that the temperature of the battery is also a factor in determining how much charge it is holding .

The temperature of the battery is available .

Can the SOC calculation factor in battery temperature .

This would change voltage readings and perhaps the issue that arises is that the 100% SOC voltage for lower temp batteries
would be higher , possibly approaching absolute 100% values .

So the question is ' Is the maximum voltage of a colder battery actually higher than the optimum temp battery ? ' .

jadnashuanh
Posts: 5036
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Range reduction in cold weather

Thu Feb 21, 2019 3:49 pm

Much of the range loss on the i3 can be overcome if you set a departure time while still connected to the EVSE. Taking the thing off of the EVSE for 4-hours prior to the test almost guarantees it will not be optimal.

One thing that wasn't clear on the i3 was whether they tested a BEV or a REx. In cold, the REx version will be (maybe significantly) less efficient than the BEV because of the heat pump in the BEV versus (only) the resistance heater in the REx. In extreme temperatures, the BEV will revert to using its resistance heater, but at 20-degrees, once the cabin temp is achieved, it should be able to maintain it with the heat pump, only using the resistive heaters (potentially) to bring the cabin temp up to set point faster than with the heat pump alone. That, too, can be overcome if you precondition the cabin while connected to the EVSE. NOte, the hysteresis on the charging circuit, the car may not reengage the EVSE if the vehicle was fully charged prior to initiating cabin preconditioning.

My personal observation over four winters in NH is, about a 30-40% drop in range if I do not set a departure time on my BEV. That value drops if I do set a departure time. The battery pack heater in the i3 is a 1Kw device, and documentation says it might run up to 3-4 hours or so, but maybe not at full tilt the entire time.

They didn't indicate what cabin temperature the HVAC system was set to, or which tends to be more efficient if you don't need to warm the entire cabin, they used the seat heaters versus cranking up the cabin temp. Personal history, you can be quite comfortable with just the seat heater on, and the thermostat set fairly low to maximize range.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above

Oleksiy
Posts: 93
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: Range reduction in cold weather

Fri Feb 22, 2019 1:26 am

CanisLupus wrote:This is what I want to suggest .
I think that , perhaps , only the voltage of the battery is being used to calculate the SOC .
It seems clear , however , that the temperature of the battery is also a factor in determining how much charge it is holding .
The temperature of the battery is available .
Can the SOC calculation factor in battery temperature .
This would change voltage readings and perhaps the issue that arises is that the 100% SOC voltage for lower temp batteries
would be higher , possibly approaching absolute 100% values .
So the question is ' Is the maximum voltage of a colder battery actually higher than the optimum temp battery ? ' .
I'm not able to check the battery voltage at 100 SOC under low temperature conditions since the pack is quite warm, about 55F, when at 100 SOC in my case (my car is in garage overnight). I have a sreenshot I took from ISTA+ to check cell balancing at low SOC
Image

The temp was about 55K as well, as you can see
Image

If you have a voltage vs. SOC plot for i3, you could check if your assumption is correct for these conditions vs summer temperature at least. However, I've seen no similar screenshots with cell voltage over 4.09V for 100% SOC yet.

As to the battery capacity related to cell temperature, I've seen some data only on Zoe here https://pushevs.com/2019/02/10/renault- ... ery-specs/. Once the pack's temperature goes to 32F, the pack can hold only 90% of its normal charge amount.

gt1
Posts: 350
Joined: Sat Nov 07, 2015 7:31 pm
Location: Baltimore

Re: Range reduction in cold weather

Fri Feb 22, 2019 10:10 am

The study itself: https://www.aaa.com/AAA/common/AAR/file ... Report.pdf
I'll read it later today.

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