Hey all. Need some guidance. I was away for three months and the circuit breaker for my charger popped two months ago. My battery is not totally dead. I was fortunate enough to pop the frunk when I was down to 2%, so I have access to the 12v. Question is, can I replace (or charge) the 12v and then recharge the car or am I looking at a tow scenario here. Thanks in advance!
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Dead battery (and I mean dead)
- Thread starter Briand19
- Start date
If the car powers up and can get into drive, you “should be” OK to get to the service center. The car should notice the 12V is toast and keep the main battery supporting all the 12V systems. I’ve seen cases where the 12V was *so* far gone we couldn’t get enough charge in it to get the contactors to close on the main battery. That one needed a tow. But if you can get the car into Drive, you should be just fine.
But I’d get that charger on it asap so you can get to the service center. Most service centers will do a 12V battery no appointment needed. Easier to ask forgiveness than permission.
If you’re comfortable changing the 12V yourself, absolutely do so.
Oh, one other note, if it’s not too late. If it’s in the garage, drop the driver’s window, so you can open the door even if the 12V is dead as a door mail.
islandbayy
Active Member
As long as the screens power up, you can charge the main battery now. Put a 12v charger on the 12v battery at a lower amperage, such as 2, 4 or 6 amps, just enough to power up the vehicle until the main pack starts charging. Once the main starts charging, you should be able to disconnect the 12v battery charger, as the car will maintain sytems via the DC to DC converter. You can replace the 12v battery yourself. Here are a couple videos for late 2014 Model S's and onward.
I would not drive it at this point until the 12v is replaced, however, at least the main HV battery will be in good standing. I'd leave it plugged in if possible.
If you are in a big hurry, you can purchase the 12v over the counter at a service center. If you can wait a couple days, I'd recommend just putting in a Ohmmu Lithium replacement. Links are in the video's description boxes.
Have they sorted out all the firmware issues? I use their product on my travel trailer (and love it!) but have been very shy to do so on my Teslas, given all the challenges as of late.
islandbayy
Active Member
The firmware issues appear to be on the MY and M3. Tesla even changed the 12v algorithm which made it worse. I'm running one in my Model S, Zero issues. I'm going to be switching over my MX as well as soon as the 12v starts to go again. Im tires of replacing the lead acids. Tesla is literally cooking them. Every failure, on both my cars, and about a dozen more I've replaced for others, each and every single one is cooked bone dry. I managed to actually revive the last MS and MX lead acids I replaced. I got to them before they were fully dry. I used a blade + drill and opened the sealed tops, and slowly added more acid over the course of a few days. Add a bit, let it soak in, repeat. Both revived batteries are happily powering other projects. Full capacity didn't come back but none the less, still usable.
I'd like to hold out for the MX one until they have the MS and MX versions with the bluetooth. The 3 and Y versions have it now.
Further, it appears Ohmmu has a firmware update for the batteries that should fix the issues with the M3 and MY.
Again, for my MS, so far so good. about 8 months only, but about 25,000 ish miles. Vampire drain is EXTREMELY low now. The lead acids required so much more "upkeep" to stay charged, and of course as they age, they bleed power, and as Tesla's poor 12v programming is cooking them, more power going into the 12v are being dissipated as heat..... Not an issue for the Ohmmu, since they can handle voltage swings, I forgot exactly, but I think it was around 11v through 16v with no ill effect for the most part.
geordi
Mr Fusion V.1
What year S are you working with that is cooking the lead batteries? I've got three different "classic" Teslas to maintain now, and if that is an issue I will need to watch for, that's helpful information.
islandbayy
Active Member
My personal cars are a 2016 Model S non-Refresh, and a 2016 Model X w/FSD Hardware.
I've done 2013's, 14's 15's 16's 17's and 18's. No 19's yet.
They WERE lasting longer. I'll use my own vehicles for example. Factory installed ones lasted about 4 years from build date, to the month. Second sets lasted 1 1/2 years in my S and 2 years in my X. Now I'm down to just over a year for each.
Even watching voltage via canbus while day to day use, I knew they were over charging the lead acids for years. 14.5 at the amperages they are using is just too high. Finally had a collection of them in my garage and started cutting them open. I save all my lead acid batteries I come across as Advance Auto gives $10 store credit for each one, nice to get stuff for free
So anyways, I know my own vehicles the best, so I can comment on my own vehicle observations the best. But each and every lead acid I cut open from others vehicles low on acid or pretty much dry. Model X's are more finnicky, the reliance and demand on the Model X, especially due to the power requirements of the falcon doors, can't handle a weak lead acid. The model s on the other hand, can survive for a LONG time with a dead 12v as long as it's not completely flat. Specifially if your model s is new enough to have the secondary mini DC to DC converter. I'm not sure off hand when that was added. It took a lot of stress off the 12v. 12, 13 and I think 14 year cars didn't have the secondary mini dc to dc. Thus theyd cycle the 12v battery more as well, as the BIG dc to dc would need to kick in to recharge the 12v.
So I've been watching voltages on the Ohmmu. Originally I was hesitant to go with a Lithium replacement, as we get below freezing here in Wisconsin, and there isn't thermal management on the Ohmmu, for obvious reasons... I was pleasantly surprised, no issues this winter. We spent a week at -10*F right before Christmas.
The Lithium can also handle voltage fluctuations better. As it's voltage range is higher than lead acid. The Model S/X/3/Y charging system doesn't go high enough to hit the Ohmmu maximum, and unless the DC to DC converter is dead, shoudn't go low enough either.
I've done 2013's, 14's 15's 16's 17's and 18's. No 19's yet.
They WERE lasting longer. I'll use my own vehicles for example. Factory installed ones lasted about 4 years from build date, to the month. Second sets lasted 1 1/2 years in my S and 2 years in my X. Now I'm down to just over a year for each.
Even watching voltage via canbus while day to day use, I knew they were over charging the lead acids for years. 14.5 at the amperages they are using is just too high. Finally had a collection of them in my garage and started cutting them open. I save all my lead acid batteries I come across as Advance Auto gives $10 store credit for each one, nice to get stuff for free
So anyways, I know my own vehicles the best, so I can comment on my own vehicle observations the best. But each and every lead acid I cut open from others vehicles low on acid or pretty much dry. Model X's are more finnicky, the reliance and demand on the Model X, especially due to the power requirements of the falcon doors, can't handle a weak lead acid. The model s on the other hand, can survive for a LONG time with a dead 12v as long as it's not completely flat. Specifially if your model s is new enough to have the secondary mini DC to DC converter. I'm not sure off hand when that was added. It took a lot of stress off the 12v. 12, 13 and I think 14 year cars didn't have the secondary mini dc to dc. Thus theyd cycle the 12v battery more as well, as the BIG dc to dc would need to kick in to recharge the 12v.
So I've been watching voltages on the Ohmmu. Originally I was hesitant to go with a Lithium replacement, as we get below freezing here in Wisconsin, and there isn't thermal management on the Ohmmu, for obvious reasons... I was pleasantly surprised, no issues this winter. We spent a week at -10*F right before Christmas.
The Lithium can also handle voltage fluctuations better. As it's voltage range is higher than lead acid. The Model S/X/3/Y charging system doesn't go high enough to hit the Ohmmu maximum, and unless the DC to DC converter is dead, shoudn't go low enough either.
islandbayy
Active Member
Part of the main DC to DC I guess, not sure exactly otherwise.
Benefit, it's lower powered. Don't need to power the main contactor, smaller one. Allows the 12v to stay charged, less vampire loss by by not needing to power main contactor and the large dc to dc. Allows the MCU to be more responsive and not go into a DEEP sleep. Makes things like Sentry Mode possible.
islandbayy
Active Member
Older cars would need to cycle the big dc to dc converter on and off, and power the LARGE main contactor. There is a separate smaller contactor, along with a lower power "smaller" dc to dc converter. For starters, you are not cycling the 12v battery as much. To reduce wear on the main contactor, the MCU and other electronics would draw from the 12v, when the 12v got low enough, main contactor would need to be activated, and the main dc to dc converter would recharge the 12v battery. Rinse and Repeat. This puts more cycles on the 12v battery, as well as more open & close cycles on the main contactor. The MCU would also need to go into a deep sleep to prevent running the 12v down as much. This all puts more cycles and wear on the 12v battery, main contactor, and the main dc to dc converter. You also get those long load times for the older Model S's to connect to the app. That is why there are more power options in the older Model S cars with MCU1 to allow the car to do a basic level sleep, sleep with cellular connectivity on so the app connects faster but the car uses more standby power, or deep sleep which takes much longer for the app to connect, puts the car into deep sleep, also requiring anywhere from 10-60 seconds for the car to fully power up when you get in.
By a separate smaller set of components, to keep the 12v topped off, and directly power the MCU and necessary electronics, with a constant power feed from the HV battery, things last longer. Less 12v battery cycles, main contactor not cycling on and off, and expensive DC to DC converter not being used as much.
My car info is per my signature, and you notice I've an upgraded MCU1 ==> MCU2. How does your description apply to my situation?
One thing I noticed immediately after my MCU upgrade was the MCU/IC coming up with no delay when I unlock the car after being parked for 24 hours undisturbed.
The other change has been a higher vampire drain even with a new 12v installed.
geordi
Mr Fusion V.1
I have two different cars with MCU two, and one with the original. Definitely longer load times on the old one. What you are probably experiencing with a higher vampire drain, is related to the computer drawing around 200 watts when it is awake. Seems like that would be coming directly from the main battery unless you have not had your 12 V replaced, and then the car is trying to constantly top that up as well.
I have not tracked vampire load on mine, none of them have sentry mode so that’s not a consideration for me, but it does seem like when they are unattended it is losing a decent amount per day.
I have not tracked vampire load on mine, none of them have sentry mode so that’s not a consideration for me, but it does seem like when they are unattended it is losing a decent amount per day.
geordi
Mr Fusion V.1
Yes, since you released the front remotely, you will have to push the emergency button to get the second catch loose, but at least you should have the room to get your fingers in and do that. On the newer ones, you’ll have to dig around and find the emergency cables in the wheel wells.
After that, then you just need to get to the contact point. If you have a nosecone car, push down on the corner of the nose cone and you can remove it once the clips release and you will find the jump points there. Otherwise you need to go digging around at the back of the frunk and find the actual battery points.
If you have a nosecone car, the front points have a 50 amp fuse so don’t try to put more than that through it, or you’re gonna have to go finding the battery anyway. You should be able to put a charger on it with a 10 amp charge rate and get everything to light up but I would leave it alone for at least an hour or two before trying to open anything else up or wake up the computers.
The computers all run off the 12 V, and that’s also what controls the charge door. So you should be OK to get it plugged in… whether sitting for this long with the high voltage at near zero caused any damage, that’s another question. Hopefully the main contacts opened and the car is actually sitting at a couple of percent rather than it completely zero.
islandbayy
Active Member
I'm not sure exactly what you want me to say??? Yes, the MCU2 comes up much quicker. It does't have the energy saving options the MCU1 had, and always is pretty much at the ready. MCU2 does draw more. I saw an immediate decrease in vampire drain after upgrading however, and even more so after upgrading my MS to a lithium Ohmmu.
Do you use third party sites or apps to monitor your vehicle? I forgot the name, but there is one that monitors all sorts of stats through their site and app of the vehicle 24/7. These prevent any kind of MCU sleep due to the constant polling of the vehicle. I tried a bunch but was loosing 10+ miles/day, so stopped
Negative. Also no accessories of any kind attached to any port.
MCU1: 1%
MCU2: 2.5%
For each 24 hours unattended, Pluged or unplugged. Installing a brand new 12V few weeks ago has not made any noticeable difference. Basically, I've a new 90kWh/350V pack, a new 12V and new MCU2 with more vampire drain than before.
The only explanation I can come up with is that MCU2 (with/without a new 12v) is just consuming more energy than MCU1, period, which is understandable due to its upgraded processor.
NewbyMaybe
Newby1Kenowby
Slow charging the 12v might bring it back depending on it's age.
Bypass it if necessary to charge the pack.
Bypass it if necessary to charge the pack.
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NewbyMaybe
Newby1Kenowby
Thanks all. I jumped the 12v battery and all came back. Have driven 150 miles since with no issues. Will probably get a new 12v to be safe.
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