eNate
Posts: 438
Joined: Mon Sep 09, 2019 5:33 pm

Re: Near Total Electrical Failure

Fri Feb 28, 2020 1:04 pm

JeffD wrote:
Fri Feb 28, 2020 10:22 am



... I consider this a catastrophic failure, which is defined as: ...

Maybe the point I was making was too subtle.

Look, it's not like the battery imploded or went supernova. It's deteriorating with time and use, just like every other battery is expected to do. The battery didn't catastrophically fail.

The fact that it reaches some magic voltage threshold where the i3 bricks itself, sure, I'll agree that can be a catastrophe for the owner, but it's ridiculous that BMW designed a system that allows it to get to this state. Can you have a "planned catastrophe" that every single i3 will go through unless the 12v battery is preemptively changed? I don't think so.

Again, the battery is decaying normally, predictably, and measurably, just like every other battery.

So back to my point about the super-important registration (it's not). If the system was actually monitoring battery health as it ages (it's not), the car would most certainly flash a maintenance warning to owner before ever getting to such a state (it doesn't).

FWIW, my 2013 Audi "required" battery registration, and that system flashes a "weak battery" message when it's time to swap in a transplant. If Audi can do that on an entry level A4 variant with an ECU that predates the i3, why can't BMW incorporate that same feature in a car that depends on the battery?

And FWIWx2, I neglected to register the Audi battery -- also an AGM type -- and instead connected a 12v charger and performed a hot swap, like for like. No ill effects suffered in the remaining 3 years I owned that car.

That's all I'm saying.
2 0 1 7   B M W   i 3   9 4 A h   B E V  O a k l a n d
 Wokeby Trunk Extension | Duosida 16A L1 EVSE
 SeaSucker Monkey Bar Roof Rack

alohart
Posts: 2074
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Near Total Electrical Failure

Fri Feb 28, 2020 2:41 pm

eNate wrote:
Fri Feb 28, 2020 1:04 pm
The fact that it reaches some magic voltage threshold where the i3 bricks itself, sure, I'll agree that can be a catastrophe for the owner, but it's ridiculous that BMW designed a system that allows it to get to this state.
For what it's worth, our 2000 Honda Insight hybrid suffered the same problem as our i3: when its 12 V battery's voltage dropped below a certain threshold, the modules necessary to enter drive mode would not boot making the car undrivable. No warning was displayed in advance of this happening. It's great that Audi seems to be able to display a suitable warning. The i3 also does this in certain situations.

The problem with displaying a warning might be that the i3's 12 V system voltage drops so much when the high-voltage system turns on (e.g., when unlocking or opening the driver's door) that it might drop below the threshold below which modules can't finish booting even though the 12 V battery's resting voltage isn't dangerously low. While the high-voltage system is booting in our i3, the 12 V system voltage can drop as low as 11.9 V before the DC-DC converter turns on even though the resting voltage of the 12 V battery is >12.5 V. When I first measured this, I was certain that the 12 V battery was failing so asked our BMW dealer to check it during our upcoming scheduled maintenance visit. The service manager told me that this is typical i3 behavior and that our 12 V battery tested normal. 2.5 years later, our original 12 V battery still hasn't failed.
Aloha,
Art

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

eNate
Posts: 438
Joined: Mon Sep 09, 2019 5:33 pm

Re: Near Total Electrical Failure

Fri Feb 28, 2020 3:07 pm

Real time, I'm with you -- the system can't tell you the battery is kaput if the system is powered by said battery.

But what the system should be capable of is monitoring trends, and tracking simple metrics such a the voltage at boot or immediately after boot, or the net current into the 12v system to return it to "charged" status, or the time it takes to get it there. Maybe even temperature?

Some of this is rudimentary and some is more advanced ledger-type monitoring, but they'd be the same bucket of tricks that the system uses to monitor the HV battery. AGM battery have a flatter discharge curve than lead acid, but it's an established technology.

And before that downward trend reaches that oh-so-predictable threshold, it flags the user. Hopefully weeks or even months prematurely, not the day of.
2 0 1 7   B M W   i 3   9 4 A h   B E V  O a k l a n d
 Wokeby Trunk Extension | Duosida 16A L1 EVSE
 SeaSucker Monkey Bar Roof Rack

JeffD
Posts: 4
Joined: Wed Feb 26, 2020 7:03 am

Re: Near Total Electrical Failure

Sat Feb 29, 2020 10:00 am

Good tip about Pep Boys. I guess I should just plan on a new battery every 3 years.

jfran2
Posts: 58
Joined: Tue Oct 30, 2018 4:20 am

Re: Near Total Electrical Failure

Sun Mar 01, 2020 4:45 am

FWIW, I just replaced the 12v battery in my 2014 Rex. The Foxwell 510 scanner I bought to register the battery wouldn't do it - I ended up returning it. Downloaded Bimmerlink and bought a Bluetooth dongle, which handled the job easily.

Return to “Problems / Troubleshooting”