12 volt battery dead

[mknox]

Yes. Tesla says keep it plugged in when not in use. You seem surprised...

I can't see keeping the car plugged in making any difference to the 12v battery. The main pack, via the DC-DC converter keeps the 12v topped up, and will come on as necessary whether the car is plugged in or not to do that. Even with the car plugged in, it does not draw any wall power at all until the main pack is down by about 2.5 kWh from the set point, and then it comes on and does a "top-up" charge.

 

[jbcarioca]

Given the debate about whether remaining plugged makes a difference my present situation my be an entertaining addition to the debate. My 12v just failed, and Tesla is now sending a truck to take it to the SC. It may be more than just the 12v, nobody knows yet. However, the car was plugged in with 77% SOC a month ago when I left. A week or so later the charge had not been replenished due to a unrelated problem with the charging station. The car then spent three weeks losing about 1.5% per day, and last showed 46% SOC when the entire car shut down and the charge plug would not even release.

So, I am about to find out later today what has actually happened. It could just be the 12v failing after nine months and 5,000 miles. It could be more complex. Anyway, I have just involuntarily joined this group. I had fond hopes of avoiding this.:crying:

 

[Electricfan]

Given the debate about whether remaining plugged makes a difference my present situation my be an entertaining addition to the debate. My 12v just failed, and Tesla is now sending a truck to take it to the SC. It may be more than just the 12v, nobody knows yet. However, the car was plugged in with 77% SOC a month ago when I left. A week or so later the charge had not been replenished due to a unrelated problem with the charging station. The car then spent three weeks losing about 1.5% per day, and last showed 46% SOC when the entire car shut down and the charge plug would not even release.

So, I am about to find out later today what has actually happened. It could just be the 12v failing after nine months and 5,000 miles. It could be more complex. Anyway, I have just involuntarily joined this group. I had fond hopes of avoiding this.:crying:

That is interesting - thanks for posting. Seems at 46% everything should still be ok. Why would it shut down and not let the charge plug be released - I guess that's strictly due to the 12V dying? Please let us know what they find.

 

[Brass Guy]

My 12V is still original, from a Sept. 2013 delivery. (Also still the original 85kWh pack.) I'm around 45k miles now. I've never seen a low 12V warning. These threads do worry me though.
I always plug in at night in the winter, but in warmer months I often don't plug in when my SOC is over 70% at the end of the day. I've always had "energy saver" on.
I wonder if my car cycles the 12V less since it has less options. The SAS is supposedly active even with the car off, so that's one system I was thinking about.
Does anybody know if the DC-DC converter is always active when the car is on, or does it cycle between the converter and the 12V battery?

 

[mknox]

My 12V is still original, from a Sept. 2013 delivery.

My March 2013 car has had its 12v replaced, I believe, twice now. But not because of any problems or errors I've been aware of. It was done "proactively" while in for other servicing issues.

 

[apacheguy]

My 12V is still original, from a Sept. 2013 delivery. (Also still the original 85kWh pack.) I'm around 45k miles now. I've never seen a low 12V warning. These threads do worry me though.
I always plug in at night in the winter, but in warmer months I often don't plug in when my SOC is over 70% at the end of the day. I've always had "energy saver" on.
I wonder if my car cycles the 12V less since it has less options. The SAS is supposedly active even with the car off, so that's one system I was thinking about.
Does anybody know if the DC-DC converter is always active when the car is on, or does it cycle between the converter and the 12V battery?

12 V replaced only once in early 2013 proactively. Energy saver on. Air suspension only actives for a brief period shortly after parking to level out the car. I've never heard it running any other time. When the car is on and you hear "click-clack" from the battery then yes the DC DC is engaged.

 

[ecarfan]

I've had my 12V battery replaced once early this year in my Dec 2013 car. Got the low 12V battery warning, called Tesla, they sent someone out a few hours later from my local SC (10 miles away) and replaced it no charge. Was told I could have kept driving it for several days if necessary. Excellent service response, but then of course I'm very close to an SC.

 

[Ingineer]

Does anybody know if the DC-DC converter is always active when the car is on, or does it cycle between the converter and the 12V battery?

The car detects when the 12v is getting low, then closes the contactors and charges the 12v from the main pack. The DC-DC is active anytime the main contactors are closed, but when the car is off (at rest) these are normally open. They are closed when charging the main pack, but open once it's charged to the desired setting, even if the charge plug is still connected. If you begin to discharge the main pack somehow, even a little, say from DC-DC activity or running the climate control remotely, the car will instead pull power from the charger if still connected.

The 12v battery has a temperature sensor and a current sensor on the negative post. Therefore if you ever add any 12v devices, NEVER connect them to the negative post directly, as this will bypass the current sensor. I've seen people adding car stereo amps doing this, and it's a bad idea! Only connect to chassis ground, or better yet, at the DC-DC converter ground.

 

[mknox]

If you begin to discharge the main pack somehow, even a little, say from DC-DC activity or running the climate control remotely, the car will instead pull power from the charger if still connected.

I don't think that's quite right. I believe it pulls from the main pack, but the charging system comes on to try and compensate. I am currently connected to a 20 amp circuit in my garage, so my car is set to pull 16 amps max. If I turn the heat on in the winter, it pulls more than 3.8 kW and even though I start drawing shore power, my battery will deplete... just not as quickly as if it were completely unplugged.

 

[Ingineer]

I don't think that's quite right. I believe it pulls from the main pack, but the charging system comes on to try and compensate. I am currently connected to a 20 amp circuit in my garage, so my car is set to pull 16 amps max. If I turn the heat on in the winter, it pulls more than 3.8 kW and even though I start drawing shore power, my battery will deplete... just not as quickly as if it were completely unplugged.

Well, obviously if it can't pull enough from the wall, then it will dip into the pack. In my observations it has tried to hold SoC. For instance say I have a charging timer set, but it's not time for charging to begin yet and the pack is lower than the charge set point. When I enable HVAC, it will still draw from the charger, but only enough to run the HVAC and hold the SoC as best it can.

 

[sorka]

If you begin to discharge the main pack somehow, even a little, say from DC-DC activity or running the climate control remotely, the car will instead pull power from the charger if still connected

This is not true. I have plugged my PD in at 80% and then set the charge limit to 60% and let it sit for days. The pack will continue to discharge at about 5 miles / day in order to keep the 12v battery charged and the HWPC will not trigger even once.

The meter shows no activation of the HWPC and the main battery continues to discharge daily all while plugged in. During this, you can still hear the contactors closing every few hours to keep the 12v battery charged.

 

[Ingineer]

Maybe there is a threshold. Try this: Enable remote HVAC and see if the HPWC contactor closes.

 

[mknox]

This is not true. I have plugged my PD in at 80% and then set the charge limit to 60% and let it sit for days. The pack will continue to discharge at about 5 miles / day in order to keep the 12v battery charged and the HWPC will not trigger even once.

The meter shows no activation of the HWPC and the main battery continues to discharge daily all while plugged in. During this, you can still hear the contactors closing every few hours to keep the 12v battery charged.

This has been my observation as well. Once it reaches a bit below the set threshold (i.e. 60%) the HPWC / UMC contactors will close and the battery will top up. If you have a timer set, it will schedule the charge and the top up will commence at your timer setting.

Maybe there is a threshold. Try this: Enable remote HVAC and see if the HPWC contactor closes.

If you activate the HVAC, either by remote or simply by opening a door, the UMC or HPWC contactors will close and start sending juice to the car. This happens regardless of whether you have a timer set and regardless of the current battery SOC or charge threshold setting.

 

[Ingineer]

Ok to clarify: If I draw a certain amperage from the HV pack, and I'm not yet sure what that is, the car will request charge support. On my car I had a large 12v load while testing this and I saw it happen. Likewise on the HVAC. Once HVAC current falls below a certain threshold it will terminate the shore power. So I'll need to run some experiments and see what the load threshold is at some point.

 

[mknox]

Ok to clarify: If I draw a certain amperage from the HV pack, and I'm not yet sure what that is, the car will request charge support. On my car I had a large 12v load while testing this and I saw it happen. Likewise on the HVAC. Once HVAC current falls below a certain threshold it will terminate the shore power. So I'll need to run some experiments and see what the load threshold is at some point.

I think this is how it works. The largest 12v load I ever used was a tire compressor pump, and it did not trigger the shore power to come on.

If I turn on the HVAC with my remote app, my dedicated energy monitor on the charging circuit will show the current spike at 16 amps (the level my car is set to) and eventually, as the car heats up or cools down as the case may be, the current that my monitor shows will begin to taper off. It sure seems like the car is trying to balance the draw on the HV pack via shore power.

 

[Ingineer]

Yes, it looks at the total energy in/out and tries to hold that. A 12v load by itself I don't think will do it, but if the contactors are already closed, and the DC-DC draws a lot, it will.

 

[sorka]

HVAC does activate the HPWC when plugged in regardless of SOC.

 

[jrreno]

This seems an appropriate thread to report our experience while travelling today. While charging at Tifton for the run to Lake City The showed roughly 168 range. The car recorded the outside temperature at 91. I got a "car needs service" and a "12 volt low" message.
Charge port was red. Air conditioning started blowing warm.
Called roadside and they advised I should not attempt to drive. One question roadside asked which I thought odd was whether I had opened the Frunk. I had not.
They were going to arrange a tow and a rental car. The rental car was going to be a problem because of the location of Tifton. While I waited for them to call back I went to Starbucks to get water for the dog ( oh yeah this is a fully packed car with wife and Golden Retriever). While gone I put down the windows and turned the power off using controls. When leaving Starbucks ( about 45 minutes after first warning) roadside calls back and says it looks as if the warning has cleared. I get back in the car and all seems normal. Check the charge port and reinsert the plug and I get flashing green!
We completed the trip home charging at Lake City and Ocala. No further issues except for the construction and pouring rain on I75.

 

[jbcarioca]

That is interesting - thanks for posting. Seems at 46% everything should still be ok. Why would it shut down and not let the charge plug be released - I guess that's strictly due to the 12V dying? Please let us know what they find.

Tesla did their usual fine job. The 12v problem was unrelated to the charger problem. Many of you may know, but I did not, that the entire electrical support of our cars comes from the 12v. That include the charging status monitoring system, which also includes the connecter release process. No 12v and the cannot know if the charging session has ended nor an it then release a connector. Thus, jump the 12v and everything will cycle on after a few minutes, as it did in mine.

As as the more knowledgable people here keep saying, no long term solution until Tesla redesigns the system to reduce the loads on the 12v and/or remove as much as possible from the 12v system. I now understand that this is quite a dilemma for a low volume manufacturer like Tesla because sourcing 12v high quality cheap parts us easy, sourcing anything else is expensive, slow and often lower quality. Hopefully Model X has improvement in this respect. I'll wager the only short term solution for Tesla is probably more robust 12v batteries.

 

[jerry33]

I now understand that this is quite a dilemma for a low volume manufacturer like Tesla because sourcing 12v high quality cheap parts us easy, sourcing anything else is expensive, slow and often lower quality. Hopefully Model X has improvement in this respect. I'll wager the only short term solution for Tesla is probably more robust 12v batteries.

One of the biggest ongoing complaints in the Prius group is the 12V battery dying. I don't know how common it is now, but many Leaf owners put a quick disconnect switch on their 12V battery, which doesn't charge while the car is plugged in. So if Toyota and Nissan can't get it right...

Of course, if a larger battery was used, it wouldn't cycle nearly as often and the problem would be minimized.