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Range on 12v battery without support from the HV battery
- Thread starter JohnBinSC
- Start date
It could just be a bad battery. I would expect the 12V battery to die in less than a week, certainly less than a month if it wasn't being recharged. There could also be a fault in the battery charger circuit.
AlanSubie4Life
Efficiency Obsessed Member
For lead-acid vehicles (no idea if any differences on new vehicles):
The 12V is only used while the car is sleeping.
However, your car is broken, so all bets are off, really.
But you can actually disconnect the 12V and then just drive, assuming your car is awake at the time. So in theory you should be able to drive indefinitely. You can definitely do without one - just have very high phantom drain (15 miles a day or so, varies from vehicle to vehicle by about 20% - more efficient vehicles of course have higher rated-mile losses, while energy loss is the same).
So distance wise, indefinite.
Time wise:
It takes about 40 hours to drain a fully charged healthy 12V battery with the sleep load. Plots posted recently showing this in context of phantom drain.
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I charged the 12v battery to 13v last night, and this morning it is down to 9v already.
The car is powered down. So something is drawing a lot of power.
Is that kind of power drain normal? Even with the car powered down?
Tesla said there was a fault in the 12v charging circuit, and I got some messages on screen about that, but I didn't read further at the time.
I will have to charge the 12v battery again to read them.
The car is powered down. So something is drawing a lot of power.
Is that kind of power drain normal? Even with the car powered down?
Tesla said there was a fault in the 12v charging circuit, and I got some messages on screen about that, but I didn't read further at the time.
I will have to charge the 12v battery again to read them.
Alan,
Thanks for that very helpful post.
If there is a problem with the support/charging of the 12v system from the high voltage system, then I'm not sure I would actually be able to drive the car without a 12v battery, since the 12v coming from the HV system may not be present.
As you said, my car is broken, so all bets are off.
I will certainly see if I can keep the car awake once I wake it up with a charged battery.
That would tell me something for sure.
I just got a quote from Tesla roadside for the tow to the service center: $1065
My car is aged out of the comprehensive 4 year warranty, but I still have the powertrain/battery warranty.
My new question is: Do HV system problems like I have described fall under the powertrain/HV battery warranty?
Thanks for that very helpful post.
If there is a problem with the support/charging of the 12v system from the high voltage system, then I'm not sure I would actually be able to drive the car without a 12v battery, since the 12v coming from the HV system may not be present.
As you said, my car is broken, so all bets are off.
I will certainly see if I can keep the car awake once I wake it up with a charged battery.
That would tell me something for sure.
I just got a quote from Tesla roadside for the tow to the service center: $1065
My car is aged out of the comprehensive 4 year warranty, but I still have the powertrain/battery warranty.
My new question is: Do HV system problems like I have described fall under the powertrain/HV battery warranty?
AlanSubie4Life
Efficiency Obsessed Member
If the car is up and operational, I would try disconnecting the negative terminal, I guess. This should force it to understand that a 12V is not installed, and make it clear to it that it needs to step up its game.
Maybe not. But if you can get the contactors closed and the car can be put in drive, then the problem is limited to the charging circuit probably. It’s very unclear though without more detail.
In theory once the contactors are closed and the DC-DC is on, it takes over all of that stuff (screen, computer, etc.)
No.
If weather is not dangerous, and it is not too far, I would just try to drive there - if you can stabilize the car.
All depends on whether you can get to a point where the car thinks it is stable.
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Hi Alan
Thanks again for the info.
I disconnected the 12v battery and charged it last night.
It seems to be behaving OK. Voltage is stable at 13V off the charger with no load.
I connected the 12v battery back up and powered on the car.
The 12v battery is holding stable at 12.6V with the load from the car.
i got the alert message VCFRONT_a192 , about the car powering down non-essential functions.
I also turned off everything I could find in the control panels.
Then I pressed on the brake pedal, and got a new on-screen message:
"Please wait while high voltage system powers up"
And the car would not let me shift into D or R.
I waited 30 minutes or more and no change, same message, and still could not shift into D or R.
So I guess I am looking for a less expensive transport of the car to the SC.
Thanks again for the info.
I disconnected the 12v battery and charged it last night.
It seems to be behaving OK. Voltage is stable at 13V off the charger with no load.
I connected the 12v battery back up and powered on the car.
The 12v battery is holding stable at 12.6V with the load from the car.
i got the alert message VCFRONT_a192 , about the car powering down non-essential functions.
I also turned off everything I could find in the control panels.
Then I pressed on the brake pedal, and got a new on-screen message:
"Please wait while high voltage system powers up"
And the car would not let me shift into D or R.
I waited 30 minutes or more and no change, same message, and still could not shift into D or R.
So I guess I am looking for a less expensive transport of the car to the SC.
AlanSubie4Life
Efficiency Obsessed Member
That message occurs if you try to drive before the contactors are closed (you can get it in any car if you get in quickly and try to shift gears before the classic clunks occur).
As long as the contactors are open you cannot drive nor can the 12V charge.
No idea what the issue is; the car is broken.
You could try using external voltage on the battery terminals and disconnect the 12V negative terminal from battery, to get the contactors to close but I doubt it would work - contactors could be busted, DC-DC could be broken, etc. Could be a PCS issue with cascading consequences. Could be a controller board problem.
Hard to know.
As long as the contactors are open you cannot drive nor can the 12V charge.
No idea what the issue is; the car is broken.
You could try using external voltage on the battery terminals and disconnect the 12V negative terminal from battery, to get the contactors to close but I doubt it would work - contactors could be busted, DC-DC could be broken, etc. Could be a PCS issue with cascading consequences. Could be a controller board problem.
Hard to know.
Hi Alan,
I went into service mode today and looked at the alerts and other stuff.
Among the active alerts, I have:
HVP_w021_PyroMiaFault
and on the HV tab/page, in the HV Battery box it says:
RedDot: State: Fault
GreenDot: Charge 62.3%
GreenDot: HVIL
RedDot: Pyro Fuse
and the Contactors are needless to say, Open.
On the plus side, on the LV page, there is a green dot by the PCS box, which also says:
Support Status: Idle
Output Voltage: 12.62V
Output Current: 0A
I assume that PCS is idle because the Contactors are open (and the 12V battery is still at 12.67V and draining).
I know what a pyro fuse is, but I don't know that this code means that it is blown and has to be physically replaced,, or whether the code just means the diagnostics found some odd behavior around it that could be reset by something easy. There are some reset buttons on the LV battery page, such as "Reset VCFRONT" etc, but I don't know what the do or are used for. I guess I will read the online service manuals.
I got a direct quote for transport of the car to the service center from $500 (to the closer SC in Atlanta) to $625 (to the SC in Charlotte).
I went into service mode today and looked at the alerts and other stuff.
Among the active alerts, I have:
HVP_w021_PyroMiaFault
and on the HV tab/page, in the HV Battery box it says:
RedDot: State: Fault
GreenDot: Charge 62.3%
GreenDot: HVIL
RedDot: Pyro Fuse
and the Contactors are needless to say, Open.
On the plus side, on the LV page, there is a green dot by the PCS box, which also says:
Support Status: Idle
Output Voltage: 12.62V
Output Current: 0A
I assume that PCS is idle because the Contactors are open (and the 12V battery is still at 12.67V and draining).
I know what a pyro fuse is, but I don't know that this code means that it is blown and has to be physically replaced,, or whether the code just means the diagnostics found some odd behavior around it that could be reset by something easy. There are some reset buttons on the LV battery page, such as "Reset VCFRONT" etc, but I don't know what the do or are used for. I guess I will read the online service manuals.
I got a direct quote for transport of the car to the service center from $500 (to the closer SC in Atlanta) to $625 (to the SC in Charlotte).
I was learned to shut the car down in the menu and wait those about 8 minutes until the contactors opened before opening the cable connector where the harnes with the OBD-connector is mounted (used for SMT).
At the service center with an electric connector issue I was (kindly) asked to remove the harness so it would not affect the detection of the fault finding job.
(They asked me to do this, as it was not original equipment and if they would brake it it might be an issue).
When I asked the technician about the shut down and wait for connectors he simply disconnected the battery and said ”this is faster, the same result.
The car was awake before and did shut down asap on the disconnect of the battery.
I get your thought about the main battery is doing all energy supplying when the car is awake, it is like that. But the system seems to be built so it can not run without the LV-battery.
There might be an need for a buffer that stabilises the voltage from the transformation from HV to LV. By the look of the 12V charging voltage it might be a switching regulator or something needing a buffer like the LV batt to stabilize the voltage and stop voltage spikes.
AlanSubie4Life
Efficiency Obsessed Member
Interesting. I have never tried this myself and I am just going off of what people who have claimed (first-hand?) that the car can be run without a 12V have said. Maybe someone else with first-hand experience could comment. Maybe specific special conditions are required for it to work?
If everything is working normally, when you disconnect the negative cable from the 12V battery post the the contactors should remain closed (until the car enters either sleep mode or you disconnect the black connector under the rear passenger side seat bottom). The car should remain driveable because the PCS would normally supply power to all 12V systems including keeping the contactors closed.
If the 12V battery does not have shorted cell(s) or similar defect, the voltage at the 12V terminals should be at APPROX one of the following three voltage levels.
14.5V PCS is actively charging the battery
13.5V PCS is maintaining a float charge level
13V to 12.4 the car is sleeping and the 12V battery is powering standby 12V subsystems
13V to ? awake and the car is NOT supplying power to the 12V buss (likely a failed PCS board). If the car is not supplying power to the 12V buss, the 12V battery might supply enough 12V power to some/all low power 12V subsystems (coolant pumps, center screen and possibly keep the contactors closed) for some variable time period.
If you wake the car (hear the contactors close) and the voltage does not rise to 13.5V or above then something is keeping the car from supplying power to the 12V buss (probably the PCS board) but it could possibly be something else. (ie..The 12V battery is supplying power)
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