Car temporarily immobile at low SOC

[pdurham]

We had a first-time experience the other day in which our i3 REX inexplicably went from around 6% to 0% SOC when sitting for about 5 hours.

Here's what happened: I drove the car on a 200-mile trip at the end of which the REX was on (though I have coded the car to permit engaging the REX at 75% SOC or less). I needed the car for an in-town trip immediately afterwards with no chance to recharge. I parked the car at my in-town destination for about 5 hours. The car was completely shut down and locked during the 5-hour period. When I was ready to leave, I drove it around the block to a loading zone parking spot so that I could put some things in the car. I didn't notice the SOC during that brief drive and it was at low speeds (partly through an alley and a parking lot) so the REX might not have come on. About 15 minutes later, I tried to drive home. The car wouldn't move under it's own power, although I could engage reverse the drive, and the SOC was 0%. The accessories and dashboard displays were fully functional.

Fortunately, I happened to be parked right beside a 120 volt outlet. (I'm not usually so lucky!) I plugged in the OUC and killed some time at a nearby café. When the SOC got to 3% (as per the smartphone app), I returned to the car to drive home. As soon as I powered on the car, the SOC went to 0% SOC and the car was again unable to move under its own power. What??!! So I then plugged it back in, and went for a meal. This second time, I got the SOC to 7%. The car was then startable and driveable, but I wanted to be sure the REX would engage. So I drove around the block and the REX engaged (can't remember whether I turned it on manually or it started automatically). I then drove about 4 miles home with the REX on the entire time (except at a couple stop lights).

I'm concerned about two things. The most important is the apparent loss of charge while the car was sitting for about 5 hours. It must have started that period at around 6% SOC (although I didn't notice the SOC when I parked it) because the driving for several miles prior to that was very easy city stop and go. My second concern is the sudden plunge from 3% SOC to 0% SOC when I attempted to restart the car after the first OUC charging session.

My only theory is that the problem was due to high temperatures and some kind of electrical load for cooling or something else during the 5-hour stop. It reached around 100º that day, and although the car was parked in the shade during the 5-hour stop, it was during the hottest part of the afternoon. (Although I've got lots of experience driving the car on the REX and also in high temperatures, until now I've always plugged it in immediately afterwards (not good for the battery to sit at an extremely low SOC). This is the first time I've let the car sit anywhere near that long after driving on the REX.) As you probably know, the car continues to cool the REX after it has been shut down and this obviously causes some battery drain. I never preconditioned the car during any part of this whole episode.

I'm going to post this same comment on the Facebook group, so I apologize in advance for the duplication.

 

[spinball]

My only theory is that the problem was due to high temperatures and some kind of electrical load for cooling or something else during the 5-hour stop. It reached around 100º that day

I think you are correct on this theory. I've been in AZ in June and it's definitely an extreme climate for humans and cars (including ICE).

 

[alohart]

Did you receive an email message from BMW warning you about your low SOC? I've received one of these messages, but I don't know exactly what triggers it. If your i3 used its traction battery pack to power the A/C compressor, fan(s), etc., to cool its battery pack which was probably quite warm after your long drive in desert heat, this would seem like the time for BMW to send you this message.

 

[pdurham]

Yes. I did get the e-mail.

 

[spinball]

They send an email automatically based on state of charge while at rest? That's interesting...

 

[epirali]

I'm curious why Rex didn't kick on. It stays on while SOC is too low until it recovers, so it makes sense it could turn on to help in cases where cooling drops the battery below trigger.

Wonder if it's a firmware issue, seems easily fixed.

 

[BrianStanier]

Rex should never activate while the car is off and locked for safety reasons. It might be in an enclosed space and produce dangerous fumes.

 

[epirali]

Rex should never activate while the car is off and locked for safety reasons. It might be in an enclosed space and produce dangerous fumes.

Makes perfect sense, but it does continue to run after driving in low SOC and parking. Haven't tried yet, so if I lock it the Rex will shut off? I usually don't lock the car in garage.

 

[jadnashuanh]

There are some things in the car that will stay on longer if it is not locked. NOt a bad practice to get into.

 

[epirali]

Rex should never activate while the car is off and locked for safety reasons. It might be in an enclosed space and produce dangerous fumes.

Well tonight I confirmed the Rex does continue to run when you turn car off in low SOC, even if you lock the vehicle. So unfortunately it will not shut off in the garage until there is a minimum SOC.