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Dead 12v Questions

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The problem is the only way to get "automotive 12V" out of the main pack is to use a DC/DC converter, or tap 4 bricks. If you use a DC/DC converter, that's fine, but how do you get it to stop working when there's a problem? Does the car have to get another pyro disconnect?

And if you tap 4 bricks, you'll get 12-16V, which is consistent with automotive 12V, but you'll cause an imbalance in the battery pack, unless you design some complicated mechanism to change which 4 bricks you're connected to in an automated manner.

I'm sure all the Model 3's with failing batteries are causing someone at HQ to wonder what would be better. If it was cheaper, I would expect Tesla to start putting LiFePO4 12v batteries in the cars.

But the truth is, 12V needs to go. Sure, there's lots of stuff that works with it already. But moving to 24V or 48V would allow smaller conductors and/or reduced power losses. It would require Tesla to source automotive equipment that worked on 24/48V. But that's the future.
The root cause of the problem is that all idle/vampire drain is drawn from the 12V battery and the battery is periodically recharged by the main battery. The drain is far larger than any other vehicle (ICE or EV) so it kills even the more expensive AGM batteries quickly (the original Model S had standard lead acid batteries and they wore out super quick!). It's not a function of mileage but time/cycles. I bet if you were to drive the car 24/7 the 12V battery would last a decade because it would never be discharged.
The question is why don't they keep the DC/DC on all the time? I have no idea.
Completely unrelated but 48V has been the future for decades. I've become skeptical it will ever happen.
 
Went to go out on a drive on Saturday, Got in my car and it was silent, the screen wouldn't come on. First I thought, try a reboot. Nothing. Then I noticed a bit of a motor whine and it seemed to be coming from the seat. The Windows rolled down really slowly. Ok, 12v is dead. Contacted roadside assistance. A flatbed was at my house in about 30 minutes. Hooked up his cable to the under-bumper wires. She's alive. The tow truck driver was able to drive it up on to the flatbed.
Under bumper wires? No need to open the frunk?
 
Went to go out on a drive on Saturday, Got in my car and it was silent, the screen wouldn't come on. First I thought, try a reboot. Nothing. Then I noticed a bit of a motor whine and it seemed to be coming from the seat. The Windows rolled down really slowly. Ok, 12v is dead. Contacted roadside assistance. A flatbed was at my house in about 30 minutes. Hooked up his cable to the under-bumper wires. She's alive. The tow truck driver was able to drive it up on to the flatbed. I contacted service via the SMS text they sent me that I may still need to get around this weekend and they provided me with a code for 3 Uber rides Which expired Sunday night. Turns out I didn't need them though.

This morning (Monday) I was contacted by Dania SC that the 12v battery was dead. They replaced it. The car is a 2019 LR AWD with about 13k miles on it. Got it in March 2019. I still don't have confirmation yet that it was fully covered under warranty. I haven't seen a bill yet. I contacted them via SMS Text they sent me that the Uber credits I didn't use expired and asked for a new one to get me to the SC that's 26 miles away. New code provided. I'll update after I pick up the car and find out if there's a bill I have to pay.
Awesome, as stated, contact Roadside Assistance for immediate work. 1 year on that battery and dead. Crazy.

Fred
 
I just got back home in my car. The battery was replaced under warranty. So no charge for the replacement.

The Roadside Assistance that came on Saturday was a flatbed tow truck driver with instructions to take it to the local SC. He didn't have any battery to replace with.

I wasn't there when the driver applied the 12v power to my car to get it driveable again. I don't know for sure if he applied 12v just to the wires sticking out of the bumper to open the frunk or direct to the battery afterward. The frunk was closed when I got there and didn't ask. But online documentation says you can't jump an M3 this way.

But I did already know that's how to enter the frunk when you have a dead battery. I don't know if there is another way to get to the battery if it's dead other than applying 12v to it.

One thing of note. According to the M3 Documentation, if the 12v battery is working and the car is locked, it should not open the frunk. Has anyone tested this? Do It Yourself - Model 3
 
I just got back home in my car. The battery was replaced under warranty. So no charge for the replacement.

The Roadside Assistance that came on Saturday was a flatbed tow truck driver with instructions to take it to the local SC. He didn't have any battery to replace with.

I wasn't there when the driver applied the 12v power to my car to get it driveable again. I don't know for sure if he applied 12v just to the wires sticking out of the bumper to open the frunk or direct to the battery afterward. The frunk was closed when I got there and didn't ask. But online documentation says you can't jump an M3 this way.

But I did already know that's how to enter the frunk when you have a dead battery. I don't know if there is another way to get to the battery if it's dead other than applying 12v to it.

One thing of note. According to the M3 Documentation, if the 12v battery is working and the car is locked, it should not open the frunk. Has anyone tested this? Do It Yourself - Model 3
Yes. I have the frunk kick sensor. It uses the tow hook frunk release wires. And it will not open the frunk if the car is locked or in drive.
 
About 5 days ago I had a bricked 3 because the 12v went dead. After about an hour, I returned to the car and it magically went back on. I did have the "Low 12v battery" message, so I made a service appointment, the first one being a week away. I did call the service center to come in, but I could not talk to a live person at all.

The car has bricked 2 more times since then and then suddenly turned on again after waiting it out (this was frustrating when I was in the middle of a forest at one point). Then, yesterday, I got a message from Tesla Service that there were no 12v batteries in stock and they needed to push my appointment out another week.

I knew my car wasn't going to make it that long, and sure enough, today my car is completely dead and after hours of sitting there will not turn on.

What are my options here? My 3 is my ONLY car and I need to get around. Correct me if I'm wrong, but I can't just grab any battery from the auto store to temporarily put in there. Everyone here has been downing the Ohmmu battery. Can I get a quick jump pack that connects to the 12v port in the Tesla?

It's Sunday officially so I can't talk to Service of course. Even if I could, it's not like they are going to give me a loaner car.

Seems to me my only option is to rent a car and pay for it myself. Is this correct? It's like a Tesla tax and that's BS.

Yeah any AGM deep cycle battery that fits should work.
 
It seems kind of sadly ironic that you could brick an EV that is literally sitting on a bed of batteries, all because of a measly 12v. :confused:

This displays my limited knowledge about these cars...but I'm wondering why (unless it's not possible?) they didn't design a back-up system that temporarily draws power from the main batteries in the event the 12v dies...

The high voltage battery is 400V. The car battery that powers everything else is 12V. It might be hard to power the converter the high voltage converter when everything is down?
 
We've been seeing a lot of 12v failures this year. I believe that it's due to an algorithm change or bug that Tesla had in their software that controls how the 12v battery is charged. AGM batteries can be damaged or their capacity reduced from both under- and overcharging. If Tesla was tweaking the way the batteries are charged to, for example, reduce phantom drain it could have caused issues. It could have also been a bug. Anybody that's had a Tesla for a while knows that sometimes bugs are introduced and later fixed. As a computer engineer, I know that it's impossible to have software that is guaranteed to always work as specified without bugs.

Interesting observation. Maybe thats why my 12V battery still reads 13.4V using my 12v socket adapter after 2.5 years - it was only last month that I updated from 2019.32.4 to 2020.32.3 (yes, I havent updated my model 3 for almost 1 full year), maybe the older updates last year still had the old 12V charging algos? Hopefully they roll out an update to fix the charging before mine dies
 
I would say it's a rare event if the main HV battery ever gets below the threshold of not being able to move the car. Certainly it has happened to people before but I would equate to the possibility of an ICE running out of gas. In my 45+ years of driving, the last two with an EV, I've never driven a car until the tank is dry. Gotten close with my BMW when the miles to empty registered 1 as I pulled into a gas station.

There's supposed to be some sort of reserve in the HV pack that's not available for propulsion so it seems like that would be enough to power a DC-DC converter for 12V even if you run out of range. It's the times when the HV battery gets taken offline (i.e., an accident), then everything powered by the 12V system will also go away. Like emergency flashers, door releases, power windows, etc. Probably not good or safe.