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12v cigarette lighter adapter plugged in for days?

Summer is coming and this is the first summer with my X so it's camping season.

I recently got a thermoelectric cooler...it's basically like an ice box but you plug it into your 12v plug in the trunk and it will keep the cooler pretty cool for you. Less bulky than my ice box since the X trunk isn't so big with the 3rd row in use, etc.

Ideally, when we go camping for 2-4 days, I'd like to just keep it plugged in inside the car all day and night.

Is this ok or will the 12v battery go dead on me? i.e., will the big battery charge the 12v battery if it notices that the 12v battery is low? I don't want to be stuck with a dead car that won't open doors, start, etc. while camping in the middle of nowhere. We usually don't drive the car much when camping so the car will mostly just be sitting there.
 

FlatSix911

Porsche 918 Hybrid
Jun 15, 2015
7,475
7,692
Silicon Valley
The big battery does charge the 12V battery as needed BUT I believe the 12 Volt outlet is not powered when the car is locked or "sleeping".

Confirmed. The 12v outlets power down when you get out and lock the car... Although I have to admit not having tested this when the HVAC is set to continue running while away. Probably doesn't make a diff tho...

Easy fix to keep the 12V outlet active ... :cool:

Ingineer said:
BTW, it's a simple matter to keep the 12v outlet in the console live all the time if desired. It's just a simple relay in fuse box #2 (the one on the passenger side under the removable cowling cover - see owner’s manual).

Simply make up a jumper consisting of short piece of 14AWG or better wire with a couple of male 1/4" spade terminals. Pull the front most passenger side relay out and insert the jumper into the now exposed 1/4" female receptacles, and you're done, the 12v outlet is now on all the time. You can quickly change it back anytime by removing the jumper and reinstalling the relay.

12v jumper 2.jpg
12V jumper.jpg
 

ShawnA

Active Member
Supporting Member
Nov 13, 2017
1,104
860
Edwardsburg, MI
That trailer brake connector has voltage at the harness at the driver's left knee on US cars...
It is dead at the 7 pin trailer connector in my March 2018 Model-X.
There was a running engineering or assembly change that dropped a wire or left out a fuse.
My Tesla resource is looking at resolving this...

Shawn
 

David99

Active Member
Supporting Member
Jan 31, 2014
4,909
7,353
Nomad (mostly US)
Please be careful when drawing power from constant 12 Volt. The car will always top off the 12 Volt battery but it won't stay on forever. I've killed my 12 Volt battery recently by having too high of a load on the 12 Volt system over night. The DCDC will supply power to the 12 Volt system to compensate for the load, but at some point it will shut down and then the 12 Volt battery dies.
 
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ShawnA

Active Member
Supporting Member
Nov 13, 2017
1,104
860
Edwardsburg, MI
Hi David99,

Thank you for your warning.
I am using it when it will work for a utility trailer that has between 10 and 15 watts of interior lighting
only when the switches are turned on...
Think of the interior lights of your ICE car.
Unlike others here, I am not running a refrigerator or other larger loads...

Also - My fuse box is a single large one directly in front of the driver next to the firewall in the frunk.
It is not a 2-part box like the picture above in post #4.

Shawn
 

David99

Active Member
Supporting Member
Jan 31, 2014
4,909
7,353
Nomad (mostly US)
Hi David99,

Thank you for your warning.
I am using it when it will work for a utility trailer that has between 10 and 15 watts of interior lighting
only when the switches are turned on...
Think of the interior lights of your ICE car.
Unlike others here, I am not running a refrigerator or other larger loads...

Also - My fuse box is a single large one directly in front of the driver next to the firewall in the frunk.
It is not a 2-part box like the picture above in post #4.

Shawn

Yes that should be fine. The car needs about 100 Watt constantly so adding 10 or 15 won't be any trouble. I have run my dash cams from constant 12 Volt for years and no trouble whatsoever. Only when the load is so high that the 12 Volt battery can't handle it and the DCDC has to basically stay on all the time, then it will eventually cause an issue.
 

FlatSix911

Porsche 918 Hybrid
Jun 15, 2015
7,475
7,692
Silicon Valley
Please be careful when drawing power from constant 12 Volt. The car will always top off the 12 Volt battery but it won't stay on forever. I've killed my 12 Volt battery recently by having too high of a load on the 12 Volt system over night. The DCDC will supply power to the 12 Volt system to compensate for the load, but at some point it will shut down and then the 12 Volt battery dies.

What is the specific use case in example... how many watts load over what time frame?

Tesla has designed the HV system to recharge the 12V system for constant parasitic loads.
 

David99

Active Member
Supporting Member
Jan 31, 2014
4,909
7,353
Nomad (mostly US)
What is the specific use case in example... how many watts load over what time frame?

Tesla has designed the HV system to recharge the 12V system for constant parasitic loads.

The DCDC converter can handle over 2000 Watt. We are talking about 160 Amps which I believe the 12 Volt wiring is not designed to handle contentiously. I have done some tests with around 1000 Watt load. Definitely way too high for the flimsy 12 Volt battery to handle so the DCDC stays on all the time. But after a certain amount of time the car will time out and shut down. I don't know what exactly the time is. It might be 12 hours.
If the load is lower the car will shut off and open the contactor in the main battery. It will still monitor the 12 Volt battery and when the voltage drops too low it will close the main contactor again, start up the DCDC and recharge. This cycle doesn't have a time limit. This will go on until the main battery is at zero (well not really zero but when it hits the bricking protection limit). So if you load isn't too much, it is fine and the car will always top off the 12 Volt battery. If the load is so high that the DCDC needs to run continuously, then you eventually hit the time out limit and the 12 Volt battery dies.
 
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ShawnA

Active Member
Supporting Member
Nov 13, 2017
1,104
860
Edwardsburg, MI
Hi Gjunky,

Unfortunately the 12V connector in the trunk is a crap shoot...
Earlier cars left it on all of the time - current cars and software generally
turn it off after a minute or so of the car being closed and empty.

There are elaborate schemes of settings that some have used to keep it on...
One setting I have NEVER had in my March 2018 X-100 MCU2 is the power saving setting.
So that string of settings will not work for me.

My wife does have the power saving setting in her 2015 Model S.

I will continue to look and listen for solutions...

Shawn
 

FlatSix911

Porsche 918 Hybrid
Jun 15, 2015
7,475
7,692
Silicon Valley
The DCDC converter can handle over 2000 Watt. We are talking about 160 Amps which I believe the 12 Volt wiring is not designed to handle contentiously. I have done some tests with around 1000 Watt load. Definitely way too high for the flimsy 12 Volt battery to handle so the DCDC stays on all the time. But after a certain amount of time the car will time out and shut down. I don't know what exactly the time is. It might be 12 hours.
If the load is lower the car will shut off and open the contactor in the main battery. It will still monitor the 12 Volt battery and when the voltage drops too low it will close the main contactor again, start up the DCDC and recharge. This cycle doesn't have a time limit. This will go on until the main battery is at zero (well not really zero but when it hits the bricking protection limit). So if you load isn't too much, it is fine and the car will always top off the 12 Volt battery. If the load is so high that the DCDC needs to run continuously, then you eventually hit the time out limit and the 12 Volt battery dies.

I have not seen this in practice with the Model S.
A 750W load connected to the remote 12V battery posts will run continuously with the HV battery recharging when needed. :cool:
 

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