NC_Taycan
Well-Known Member
- First Name
- Lewis
- Joined
- Oct 13, 2020
- Threads
- 12
- Messages
- 810
- Reaction score
- 713
- Location
- Wake Forest, NC
- Vehicles
- '12 Tesla Model S P85, '17 Cayenne S, '20 Taycan Turbo
What I've managed to gather - the 12V system will wake up the DC-DC converter and 800V battery to re-charge the 12V when it gets low. If this happens while charging, you will see charging pause while the 12V is being recharged. However after some limit is reached on the number of times this is done in some time period (don't know what those magic numbers might be) the wake-up to re-charge stops. I won't pretend I have any idea why it's designed this way. If 12V drain continues from that point, the 12V battery will eventually reach a low enough state of charge that it is disconnected from the vehicle (latched off) and the car is now completely dead. Once it gets to that state, you are "jump-starting" the 12V system. But yes there's 12V drain. Call it phantom, but it's coming from the charging hardware (in the car) and PCM both being active, and possibly the OTA communication module being active. These things can all be controlled by software, so it should be able to be fixed entirely in software. The charging hardware in the car is remaining on because there is some strange state where the external charger is waking up the in-vehicle charging hardware but not charging (e.g. because charging is paused, or because charging has finished but the handshake to shut down the external charger wasn't received or interpreted properly). This can happen with the Porsche charger (it happened to me) and it can happen with non-Porsche chargers. Only take-aways are to completely avoid using the Connect app once the car is connected to the charger until you are near ready to drive. Locking the car while charging may help. Keeping the key out of range of the car while charging may help. I don't think we have a report of 12V dying while the car is NOT hooked up to a charger.Clearly the problem is related to some kind of phantom drain on the 12v battery. But another issue is that it clearly doesn't keep the 12v battery charged using the car's main battery bank, which is baffling. You've got a bazillion kwh battery sitting there, and it may even be connected to AC power. Yet the 12v battery dies. Perhaps it only charges the 12v battery when the car is being driven, like an ICE car? Very odd.
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