Recently, there is a very special matter that the National Highway Traffic Safety Administration (NHTSA) of the United States has announced an investigation into potential power loss issues for MY2020 and MY2021 Porsche Taycan electric vehicles. The issue mainly manifests as sudden power loss during driving without warning, which is based on nine consumer complaints in the United States.
Part 1: Information dynamics released by NHTSA
1）Information released by NTHSA
Currently, according to NHTSA’s description, the most peculiar thing is that insufficient power in the 12V battery may cause the entire power system to fail, resulting in sudden power loss of the vehicle. The most dangerous thing is that while driving in various driving states, the Taycan system suddenly loses power without any warning to the vehicle owner. In the process of vehicle shutdown or after shutdown, there is no error message related to the battery problem. Even six cases reported that the problem could not be solved by restarting the vehicle. In this regard, there are some differences, and some vehicle owners will receive warning messages, as shown below.
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1)
Original text from the NHTSA report:
The Office of Defects Investigation (ODI) has received nine complaints from vehicle owners and a few field reports alleging a loss of motive power while in motion at any speed without warning to the driver. The complaints and reports involve Model Year (MY) 2020 – 2021 Porsche Taycan vehicles. The Taycan is an 800-volt battery electric vehicle with an auxiliary 12V battery. A loss of charge in the 12V battery may deactivate the entire electrical system and prevent the vehicle from operation. All complaints allege that loss of motive power occurred without warning and error messages about a battery fault displayed during or after the vehicle stalled. Six complaints allege an inability to restart the vehicle once they lose motive power.
2)
What kind of battery does the Taycan use?
The Taycan uses a phosphate iron lithium battery for its 12V battery, as shown below, which was purchased as a spare by a car owner.
After some research, I found that this is a battery made by Wanxiang A123 at their factory in the Czech Republic. It uses 40Ah and has a nominal voltage of 13.2V (possibly 2P4S), and is designed with dual-terminal Taps.
However, the biggest issue here cannot be explained: once the LFP battery enters the low state of charge (SOC), the 800V to 12V DCDC does not work properly. As shown in the figure below, even if the switch inside the 12V battery is turned off, this 800V to 12V DCDC should be able to output 240A of current to keep the overall system working according to our normal logic. In the current situation, the extreme and serious problem is that once the 12V battery is dead, this DCDC does not work properly, which cuts off the current of the entire system.
Note: Although it is written in the user manual, if the 12V battery is automatically disconnected while driving, then there is a problem with the software.
According to Porsche’s previous materials, the low-voltage 12V energy management is implemented in the software of Volkswagen’s gateway management. We dare to speculate that there are two possibilities.
1) A123’s SOC estimation may have deviation under certain conditions, which trigger self-protection of LFP cells through continuous discharge, leading to 12V battery disconnection under certain working conditions.
2) The low-voltage energy management unit of this gateway may not have been managed properly. Since the EE system leakage of Taycan is not small, there may be a large deviation in the SOC state obtained by the gateway controller due to the self-discharge of LFP battery or being placed for a period of time.
I think only when both possibilities are met at the same time, can the Taycan cut off the 12V battery while driving on the road and even fail to keep the DCDC running, or even fail to power up again.
Summary
The main problem with electric vehicles is that they use a small 12V battery that easily drains under various connected features, causing power loss during driving. It’s unbelievable that Porsche still uses such setup.
This article is a translation by ChatGPT of a Chinese report from 42HOW. If you have any questions about it, please email bd@42how.com.