alohart
Posts: 1255
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sun Jul 08, 2018 4:11 pm

sogorman wrote:I am sure the cells are not imbalanced, I have had the car at fully charged connected to a L2 for two days before running the first test in my google doc.

According to British i3 owners who have spoken to BMW engineers, cell balancing occurs extremely slowly due to the high resistance resistors used to discharge high charge level cells. They have written that a severely imbalanced battery pack could take weeks to rebalance completely. If true, and if the charge levels of the cells in your battery pack vary significantly, 2 days of cell balancing might be inconsequential.

I wish we had a way to measure charge level imbalance so that we could determine whether cell balancing were required.

[quote="sogorman"]Yes the car will attempt to cool and regulate the HV pack temperature when plugged into L2 even at 100% SOC./quote]
Was this with battery pack preconditioning enabled? I know that this would result in active cooling occurring if the battery pack temperature were sufficiently high. If cooling could occur whenever an EVSE is plugged in but not actively charging, why would the preconditioning functionality be needed?
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

Oleksiy
Posts: 13
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sun Jul 08, 2018 11:58 pm

sogorman wrote:I really can't decide whether to further push the cells into an unhealthy state and trigger the 30% warranty or try and baby it.

I think you would do the former inadvertently whatever strategy you choose to employ. Charging up to 100% and trying to balance cells would lead to accelerated degradation. And it would be difficult to employ a 80%-20% use approach anyway given the already degraded battery with the correspondingly decreased range. You can't control the weather either, temperatures over 100F will just add to this process.

sogorman
Posts: 8
Joined: Sat Jul 07, 2018 1:00 pm

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Mon Jul 09, 2018 5:47 am

@Oleksiy you are probably correct. with the low available total capacity (~15.0kWh) and my daily commute (~49Mi round trip) I will be forced to cycle the pack from about 100% - 5% every day in the phoenix heat. To your point whether I want to or not this will accelerate the degradation and the further the pack degrades the further I must discharge it every day.

I am used to babying my Tesla's pack the best I can (charge only to ~80% SOC every day, pre condition for about 10 minutes before every trip, etc...) with the i3 I had hoped to do the same but BMW cripples us in some regards (not being able to set charge target SOC) and my i3 with the battery in the shape it is will require near 100% DOD every day just for getting me to and from work.

arodi3
Posts: 4
Joined: Thu Apr 26, 2018 10:21 am

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Mon Jul 09, 2018 7:40 am

@sogorman I don't think that it has to be a level 2 charger for the i3 to cool the cells while at 100% SoC; I just have a level 1 at work and I observe the compressor running in the middle of the day on hot days.

@alohart Yes, I have heard the compressor running while my car is parked and at 100% SoC. My car is often at 100% SoC since it is just a 10-mile drive to work for me. During the winter, I don't hear the compressor coming on randomly while the car is parked.

i3Alan
Posts: 241
Joined: Wed Jul 09, 2014 4:08 pm

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Mon Jul 09, 2018 8:19 am

The Batt. Kapa Max. on my i3 service menu is 15.9 kWh, or 80% of new spec of 19.8, and even less of actual when new, which was just over 20.

My '14 i3 BEV is just shy of 30K miles. I live in the Phoenix desert, but the i3 is rarely parked outside, and the garage rarely gets much above 90 degrees. In the summer, I keep the i3 plugged in (L2) whenever home so that the cooling system may run as needed, but when cooler, I typically will not plug in unless the charge is below 75% (per the display) except when I know I will need a full charge the next day, which is typically 2 days/week.

I suspect I have about a year or so to hit the battery warranty replacement, as battery degradation tends to speed up rather than slow down (all else the same). Unfortunately, before I get there, there is one weekly trip I make that is already starting to push my round-trip remaining range.

sogorman
Posts: 8
Joined: Sat Jul 07, 2018 1:00 pm

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Mon Jul 09, 2018 8:50 am

@i3Alan Sounds like we are in the same boat. With the long commutes the further the pack degrades the further the daily DOD (depth of discharge) cycles get... it's a cycle that is self destructive at a certain point.

I think I am about 1 year away from a new pack as well which I guess is not all a bad thing. If you don't mind me asking what part of town are you in?

gt1
Posts: 237
Joined: Sat Nov 07, 2015 7:31 pm
Location: Baltimore

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Mon Jul 09, 2018 12:50 pm

sogorman wrote:I am used to babying my Tesla's pack the best I can (charge only to ~80% SOC every day, pre condition for about 10 minutes before every trip, etc...) with the i3 I had hoped to do the same but BMW cripples us in some regards (not being able to set charge target SOC) and my i3 with the battery in the shape it is will require near 100% DOD every day just for getting me to and from work.

I heard that when you charge a Tesla to the indicated 100% you will reach the actual 100% charge on the battery, while indicated 100% on i3 correspond to 80-90% of the charge.
There is also a question if the dashobard SOC meter is accurate and linear. I hasn't paid much attention to i3, but my Chrysler Pacifica can go about the same distance from 5% to1% as from 1% to 0.

sogorman
Posts: 8
Joined: Sat Jul 07, 2018 1:00 pm

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Mon Jul 09, 2018 2:15 pm

@gt1 I agree that the Max Kappa. Kwh reading in the diagnostics is only an estimate made by the BMS which is why I did an actual road trip recording distance, consumption, etc... to calculate the actual usable energy details here: https://docs.google.com/spreadsheets/d/ ... sp=sharing

As to
I heard that when you charge a Tesla to the indicated 100% you will reach the actual 100% charge on the battery, while indicated 100% on i3 correspond to 80-90% of the charge.
You are correct to a degree. The original usable capacity of the i3 battery as stated from BMW is 18.8 kWh of the actual 22 kWh. This indicates that there is 1.2kWh (5.45%) of SOC that is reserved by the BMS. Some of that is for anti bricking on the low end which would mean that "fully charged" is to your point not 100% SOC but closer to 95%.

alohart
Posts: 1255
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Mon Jul 09, 2018 3:11 pm

arodi3 wrote:@alohart Yes, I have heard the compressor running while my car is parked and at 100% SoC. My car is often at 100% SoC since it is just a 10-mile drive to work for me. During the winter, I don't hear the compressor coming on randomly while the car is parked.

The battery pack is warmed by resistance elements rather than the heat pump, so the heat pump compressor would not run to warm the battery pack.

BMW's top electric vehicle technical services manager in the US answered the following questions:

Q. Will the car ever turn a battery warming on by itself if the battery temperature gets critically low. For example, the car is parked outside and plugged in and the battery temperature drops below 30 degrees, will the preconditioning turn on and warm the battery up without owner intervention?
A. No. User intervention is required for battery preconditioning. If the battery temperature is very low, it will be outside its normal operating temperature. As a result, the power output and usable energy of the battery will be reduced.

Q. How about if it gets critically hot – over 105 degrees?
A. If the battery temperature is higher than the optimal operating range and preconditioning is activated, the battery can be cooled. This is not very common due to the fact that the battery is such a high thermal mass, is located close to the ground, and is not exposed to direct sunlight.


With the limited capacity of an i3's battery pack, it makes sense that battery pack preconditioning, either heating or cooling, would not occur unless the car is in drive readiness state, is being charged, or has had battery pack preconditioning enabled with the time being less than 3 hours prior to the set departure time.

When you heard the A/C compressor running, were any of the above conditions being met?
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

alohart
Posts: 1255
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Mon Jul 09, 2018 3:19 pm

gt1 wrote:I heard that when you charge a Tesla to the indicated 100% you will reach the actual 100% charge on the battery, while indicated 100% on i3 correspond to 80-90% of the charge.

For example, a 60 Ah i3's battery pack has a total nominal capacity of 21.6 kWh with a nominal 18.8 kWh usable. That means that 18.8/21.6 = 87% of the total capacity is usable. We know that a significant percentage of this cannot be accessed at the low charge level end which means that an indicated 100% charge level is likely 90-93% of the absolute full charge. In this charge level range, the capacity degradation rate, especially at high temperatures, is significantly faster than at a charge level 10% less (i.e., an indicated charge level of ~90%).
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

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