Model 3 12v battery dead

[Gasaraki]

Much appreciate the counsel. But once jump-started, can the car run if the 12v battery is dead ?
If that is true, then all the electronics can run off the main battery pack, right?

If the 12v battery powers electronics, then wouldn't it be better to jerry-rig in a 7-9 AH $20 lead acid battery that could (?) provide enough amperage to start up the electronics and accept a charge from the mothercircuits ?

Or is it known that much amperage is required for the car to drive and start ok?

I'm confused. Is it that normally the 12v battery is powering a lot of stuff but in parallel with a converter off the main battery, making it necessary only before the system is fully started? In that case what's minimum capacity required to get the car booted up, and would a small 7-9 AH battery be enough to get going out on the road if the real 12v battery fails?

Where can I find out what exactly normally runs exclusively off the 12v battery? Is there a diagram anywhere?

The car will usually run because the "alternator" is converting the main battery power to 12V, actively charging the 12V battery. If the 12V is completely dead where it won't even take an amount of charge, then I don't think you can drive the car.

Usually even a "dead" 12V will take a charge if you actively charge it, it just won't hold a charge.

 

[lolder]

Everything except AC and drive motors runs off 12 vdc. The HV contactors are open when the car is asleep but the 12 vdc is on and powering lots of stuff. It's voltage is monitored and when low the HV contactors close and the 12 vdc is charged. Recent software updates measure how often that happens and as the 12 vdc battery ages it occurs more often. A warning message now appears to change 12 vdc battery soon when battery is nearing end of life.

 

[pnwadventures]

Everything except AC and drive motors runs off 12 vdc. The HV contactors are open when the car is asleep but the 12 vdc is on and powering lots of stuff. It's voltage is monitored and when low the HV contactors close and the 12 vdc is charged. Recent software updates measure how often that happens and as the 12 vdc battery ages it occurs more often. A warning message now appears to change 12 vdc battery soon when battery is nearing end of life.

I thought it was AC and heat, plus seat heaters, that tab off of the HVB.

 

[android04]

I thought it was AC and heat, plus seat heaters, that tab off of the HVB.

Just the drive motor or motors, the AC compressor, and cabin heater run off the high voltage. In newer cars with the heat pump, the AC compressor and cabin heater are replaced in one unit by it.

 

[android04]

I thought it was AC and heat, plus seat heaters, that tab off of the HVB.

Just the drive motor or motors, the AC compressor, and cabin heater run off the high voltage. In newer cars with the heat pump, the AC compressor and cabin heater are together in one unit.

Much appreciate the counsel. But once jump-started, can the car run if the 12v battery is dead ?
If that is true, then all the electronics can run off the main battery pack, right?

If the 12v battery powers electronics, then wouldn't it be better to jerry-rig in a 7-9 AH $20 lead acid battery that could (?) provide enough amperage to start up the electronics and accept a charge from the mothercircuits ?

Or is it known that much amperage is required for the car to drive and start ok?

I'm confused. Is it that normally the 12v battery is powering a lot of stuff but in parallel with a converter off the main battery, making it necessary only before the system is fully started? In that case what's minimum capacity required to get the car booted up, and would a small 7-9 AH battery be enough to get going out on the road if the real 12v battery fails?

Where can I find out what exactly normally runs exclusively off the 12v battery? Is there a diagram anywhere?

This is for the LR RWD. An AWD will have the additional high voltage cables running to the front motor. Newer cars with the heat pump replace the two sets of cables going to the AC compressor and cabin heater with one set.

 

[Fernand]

Thanks!

 

[AlanSubie4Life]

The HV contactors are open when the car is asleep but the 12 vdc is on and powering lots of stuff

It is not really lots of stuff. Just maybe 6-10W when the DC-DC is not on? I mean literally it may be a great number of systems, but the overall load is very low.

Just the drive motor or motors, the AC compressor, and cabin heater run off the high voltage. In newer cars with the heat pump, the AC compressor and cabin heater are replaced in one unit by it.

Yes, but to be clear, except for very brief periods perhaps, everything is running off the DC-DC which is running off the HVB. Once those contactors close that DC-DC powers up and the 12V battery is no longer loaded.

As far as I can tell it is one of the reasons the car is so sluggish before the contactors close - there just is not much that can be powered (or that Tesla wants powered - to avoid killing the 12V). The screen powers on very briefly without closed contactors (I think), but there is not much you can do with it.

For sure, if you have the seat heaters on, they are running off the HVB (via the DC-DC which powers them with ~13-14V.

 

[brulaz]

It is not really lots of stuff. Just maybe 6-10W when the DC-DC is not on? I mean literally it may be a great number of systems, but the overall load is very low. ...

Yes that agrees with a lot of longer term phantom drain reports, 150-250 Wh per day.

 

[lolder]

I think the 12 vdc battery has only about 500 wh capacity so 250 wh/day is quite a load. Most modern cars have this problem.

 

[JackLuminous]

Mine died a sudden death. Car drove fine in the morning, no alarms or warnings. Went out at lunch, and it was dead as a doornail. Fortunately I was at home, so I opened the frunk using the wires under the little disk in the front bumper, exposed the battery and attached a battery charger. Within a second of attaching the charger, the contactor went "Clunk!", the lights came on, and the car was driveable, but now I had warnings about the battery. Drove over to the SC, and they graciously installed a new battery for me under warranty.

What battery charger would you recommend -as a part of a wee emergency toolkit?

 

[llamafilm]

With a dead 12V battery, how do you shift into neutral to get loaded onto a tow truck? I haven't seen a physical shift lock mechanism like some other automatic transmission cars have.

 

[jrmt23]

I have one of those portable jumpstart batteries with my current car, but i havent taken delivery yet of my Model 3.

I was wondering, if the 12V battery died, where would be a good place to store this portable jump starter? In the trunk? The frunk?

 

[pnwadventures]

I have one of those portable jumpstart batteries with my current car, but i havent taken delivery yet of my Model 3.

I was wondering, if the 12V battery died, where would be a good place to store this portable jump starter? In the trunk? The frunk?

Frunk. Then you can jump the frunk to retrieve it to jump the 12v.

 

[jrmt23]

Frunk. Then you can jump the frunk to retrieve it to jump the 12v.

Will the frunk still be able to be opened with a dead 12v battery?

 

[Matsayz]

Will the frunk still be able to be opened with a dead 12v battery?

No. You’ve got to pop the little cover off the front of the bumper, “jump” the two wires there (a small 9volt battery will even do the trick), then remove the cowel to reach the 12volt battery, jump it so you can open the door and access the screen to put it in “tow mode”.

 

[smartypnz]

No. You’ve got to pop the little cover off the front of the bumper, “jump” the two wires there (a small 9volt battery will even do the trick), then remove the cowel to reach the 12volt battery, jump it so you can open the door and access the screen to put it in “tow mode”.

Also, as someone mentioned... a good idea to place a 9 volt battery in a small ziploc bag ln the bumper cover. Cuz who carries one in their pocket?

 

[Matsayz]

Also, as someone mentioned... a good idea to place a 9 volt battery in a small ziploc bag ln the bumper cover. Cuz who carries one in their pocket?

I never leave home without my trusty 9volt, Duracell FOR LIFE! But I guess I'm the only one...

 

[neurocutie]

No. You’ve got to pop the little cover off the front of the bumper, “jump” the two wires there (a small 9volt battery will even do the trick), then remove the cowel to reach the 12volt battery, jump it so you can open the door and access the screen to put it in “tow mode”.

the implication being that anyone can pop open the Model 3 frunk with ease and steal whatever's inside, including the 12V battery...

 

[android04]

the implication being that anyone can pop open the Model 3 frunk with ease and steal whatever's inside, including the 12V battery...

Not unless you leave the car unlocked. The frunk will only jump open if the 12v battery is dead or the car is unlocked.

Also, as someone mentioned... a good idea to place a 9 volt battery in a small ziploc bag ln the bumper cover. Cuz who carries one in their pocket?

A better idea is to put an A23 battery in a ziplock and stick behind the tow hook cover. That's what I did and I've tested to make sure it works. The A23 battery is a tiny 12v battery that's used in my keyfobs.

 

[pnwadventures]

Not unless you leave the car unlocked. The frunk will only jump open if the 12v battery is dead or the car is unlocked.

Really? That's excellent, if true. Do you have a reference?