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Jump-Starting 12V Battery Charger PSA
- Thread starter Slipstream
- Start date
PianoAl
Active Member
android04
Active Member
I haven't had to replace mine yet, but this is the one I will get when I do https://www.oreillyauto.com/detail/...inum-battery-group-size-51r/ssbq/51rplt?pos=0
Had the battery die in my 3 (2018) and got it going with a Gooloo (sp?) jump box worked great. (Note that all this process with a jump box is now in the Tesla doc under 'car won't drive'). Some have said elsewhere that Roadside will do 12V replacements (got the car home from the 2nd level of a garage at work) and messaged them. Nope, since I can drive it now, contact the SC. Mobile: next is a week out. Gonna see if they update it to be closer or just drop by later. Got the car charging and kept awake with Sentry.
BTW, had a problem with getting the cover off, and snapped one of the plastic hooks/tabs on it. It really did not want to move no matter how I pressed, etc. Any suggestions there on what I was doing wrong?
BTW, had a problem with getting the cover off, and snapped one of the plastic hooks/tabs on it. It really did not want to move no matter how I pressed, etc. Any suggestions there on what I was doing wrong?
RichAZ/CapeCod
Member
Very interesting and informative series of posts. Couple of thoughts:
If the 12v battery is kept up to full charge with the motive battery pack how the heck does the 12v go flat? Age? Sitting outside when it's cold with a low SoC maybe?
Would it not be prudent to do a "preemptive strike" and replace the 12v on our Teslas every three years or so?
Rich
If the 12v battery is kept up to full charge with the motive battery pack how the heck does the 12v go flat? Age? Sitting outside when it's cold with a low SoC maybe?
Would it not be prudent to do a "preemptive strike" and replace the 12v on our Teslas every three years or so?
Rich
Gauss Guzzler
Safety Score = 42
Yeah, the tow cover is easy to remove if you know the exact right angle to push it, nearly impossible if you don't.
The angle seems unnecessarily senseless and is not noted in the manual in any place you'd be able to find it, but it is buried in there somewhere:
The angle seems unnecessarily senseless and is not noted in the manual in any place you'd be able to find it, but it is buried in there somewhere:
android04
Active Member
The 12v battery isn't being maintained 24/7. The car goes to sleep and disconnects the high voltage battery, so at that point the 12v battery is on it's own fire a while until the car wakes up again to top it off. This is why the majority of 12v battery failures are encountered after the car had been parked a while and the owner tries to open the door. The 12v battery is too weak to power up the high voltage system that maintains it. If the battery is weak or has a shorted cell, it may seem fine as long as the car is awake and powering the 12v system through the high voltage battery and DC to DC converter. As soon as the car goes to sleep and that lifeline disconnects, that's when you encounter issues. Tesla has updated their charging and monitoring algorithms to try and detect weak batteries before they leave you stranded and to keep the car awake if they determine the chances are high of the 12 battery not being able to wake the car again. But their algorithms are not perfect and cannot be. So sometimes people will be left with a car that won't wake up until they get it jump started or the 12v replaced.
davewill
Active Member
More likely the person has parked somewhere and is unable to start the car. Once the car is started, the main battery powers the system through a DC-DC converter, and it should stay alive until the car is shut down. That said, I wouldn't make a habit of jumping the car for fear of damaging the electronics.
That's likely the "short circuit protection" in the noco jumper. It won't activate unless it senses some level of voltage from a typical "just about dead" battery.
Thankfully the amperage needed to pop the frunk is so minimal, one of these N21/N23 style batteries would do the trick:
android04
Active Member
Like dmurphy mentioned, the "reverse polarity protection" kept the NOCO jump starter from putting power onto the two wires because it doesn't detect any voltage on them (since they aren't connected directly to the 12v battery). It will still work but you have to push the bypass button on the NOCO to force it to output power (read the manual).
Any concerns about storing a lithium jump starter in the frunk of a black M3 that sometimes sits in the sun on a hot summer day?
My model of lithium jump starter (a Schumacher SL1396) says to store it at -4–140°F (-20–60°C). That seems likely to be exceeded in the frunk at times.
I'm less worried about damaging the starter itself (although that's also a concern), more worried about causing a fire that damages the vehicle.
My model of lithium jump starter (a Schumacher SL1396) says to store it at -4–140°F (-20–60°C). That seems likely to be exceeded in the frunk at times.
I'm less worried about damaging the starter itself (although that's also a concern), more worried about causing a fire that damages the vehicle.
I don't think a closed in dark area with no sunlight access would get that hot. Car cabins get that hot because of the greenhouse effect, where the sun's energy is able to come in through the glass, get absorbed by materials inside, converted to heat, and then not escape, so it continues to build up without equalizing it to the outside air. I don't think a dark frunk with no windows will do that. It's basically shaded.
RayK
Active Member
I'd say that would be true if you have a completely insulated medium between whatever the sun is shining on and the interior of the frunk. Let your car sit out in the sun for an hour or two. Pop the frunk and feel the inside of the hood. That heat is being transferred into the air inside the frunk. Heat energy is always going to try to stabilize between two different environments unless you put something, like a vacuum, in the way. At least that's my thoughts.
Simple experiment: put a digital thermometer inside the frunk and see what happens after an hour in the sun. I'd be very surprised if it's not hotter than the ambient temperature around the car.
"hotter", yes, probably. But I said not "that" hot, where it was suggesting 140 degrees Fahrenheit. That's what my car's cabin gets to in the summer, and the frunk area definitely isn't getting that hot.
RayK
Active Member
Okay, experiment performed. My car faces north in my driveway. It's been sitting there all morning. Air temp was 92F as measured by my home weather station (roof mounted sensor). I opened the frunk and put the thermometer inside and closed the hood for 30 minutes. This is what it read when I opened it up:
Frunk was empty and the thermometer was resting at the front edge on the WeatherTech mat. I'm surprised that it only got to just under 115F. Mostly because the middle of the hood measured 171F with the infrared thermometer, about 18" from the MSM paint.
So yes, you are correct that it doesn't get to 140F. It does get warmer than ambient but only ~20 degrees hotter.
RayK
Active Member
Addendum: The Tesla app reports my interior temperature is 137F as of right now (2:53pm), almost 90 minutes after my frunk measurement. I forgot to check it earlier. No additional tinting on the windows but I do have a semi-permanent interior roof shade (front only) and a temporary, metalized windshield shade.
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