On the 2nd of April, King Song sent out their investigation report of the instances of the fire that happened the 27 Mars in New York.
There looks like some things happened during the failure, first, the hall sensor signal issued the wheel cut off, and the motherboard did not stop giving the motor power due to a motherboard firmware bug, which short-circuited the motherboard MOS.
King Songs shows how a company should react in case of a failure with a full investigation to find the root cause of the issue. Read more in the report below.
KING SONG OFFICIAL ANNOUNCEMENT
Analysis Report of EUC EAGLE Sample
Dear Customers and Riders Worldwide,
Firstly, King Song would like to express our sincere apology to all of you again. We feel deeply grateful for all your support and belief in us.
King Song has conducted comprehensive investigation, testing, and analysis to help locate the root cause this week. We also re-produced the incident under controlled circumstances to further investigate the cause of the incident. For the battery test video, please refer to the video we posted on YouTube, the name of video is: Tests Related to the Battery Pack of S22.
Upon the testing and the investigation, we now share with you the Analysis Report and the solutions as below:
1. Analysis of Causes
A. According to user feedback, the unicycle experienced a loss of power during the riding process.
B. In the video the EUC suddenly lost power while riding. After analysis, it may be that the system detects an error of hall sensor signal during the riding, resulting in failure to output power. At this time, the software should play a protective role. However, after the vehicle fell to the ground due to a software bug, the power output could not be cut off in time, resulting in mosfet being shorted.
C. The product design should be such that the battery protection system takes effect and turns off the power output. However, the actual phenomenon was that the battery began smoking and eventually catching on fire, which means that after the motherboard is short-circuited, the battery protection function failed to initiate, resulting in a short-circuit and fire.
D. Key points of incident analysis:
A: Why did the power cut off during riding?
B: Why did the MOS short after the power cut?
C: Why did the battery protection system fail?
2. Analysis of motherboard problems
A. The firmware model of the customer riding vehicle is KS-S20B (the official version of the first batch of KS-S20 shipped worldwide). This firmware is a test version and has not been finalized.
B. We have asked the customer to remove the motherboard and send it to us, it’s due for arrival within the next few days. After receiving the motherboard, we will analyze the analyze the motherboard.
3. Battery fire failure test
After actual testing and analysis, the fault is confirmed as output overcurrent short circuit protection failure, the following is the test photo:
Output Short Circuit Test
After several output short-circuit tests, the battery output short-circuit fails, and the nickel sheet burns red directly. If the short-circuit continues, the battery will catch fire.
4. The reason why the output overcurrent short circuit was not protected
Under normal circumstances, when the battery output is experiencing an over-current or short-circuit, the protection board will turn off the MOS for the first time after detecting it, and plays a protective role. If the software system fails, or the MOS is short-circuited due to a fault, and the MOS cannot be turned off, the protection fuse should work at this time, and it will be blown directly to play a secondary protection role.
After our actual test, we found that when the output is short-circuited, not only the MOS is not turned off, but also the fuse is not blown. At this time, it is shown that the nickel sheet of the battery has burned red, and there is a risk of fire.
In a more detailed breakdown; due to hall sensor signal issue the wheel cut off, and the motherboard did not stop giving the motor power due to a motherboard firmware bug, which short circuited the motherboard MOS.
At this phase because of a bug in the BMS the MOS should turn off to protect all components, but that did happen. Instead the BMS MOS turned OFF and ON due to the firmware bug, and the time between ON and OFF states were so short that it did not blow the fuse and hence the constant power output from the battery led to the eventual fire incident.
For the solution of the problem, please refer to the below;
1. Mainboard software improvement solution
The latest software version V2.19 update includes:
A. Optimized the log record of the motherboard;
B. Optimized BMS warning display and board lift response;
C. Optimized the motor drive part to make the output power larger.
D. Fix known bugs
E. Optimize the Taillight lighting effect.
Note: We have released the latest version today, riders must update the software to ride safely to the latest version to ensure the a safe experience.
2. Battery BMS software improvement solution
The latest software version V2.0 update includes:
A. Added the function of keeping the protection state, so that the protection function can be maintained before and after switching on and off;
B. Through software optimization, when the output short circuit or overcurrent protection occurs, normal function can be restored by inserting the charger or removing the load;
C. Add short circuit wake-up function, when a short circuit occurs, the system can immediately start engaging in order to protect the battery;
D. Increase the battery automatic balance function; E. Optimize the power display to make the power display more accurate;
Note: We have released the latest version today, riders must update the software to ride safely to the latest version to ensure the a safe experience.
We have sent out the battery and BMS to third party for analysis, and we will post the testing result once we get it. To prevent further incidents, we will upgrade the current firmware to replace the old version. From this point onwards, in order to make easily identity the difference we are now officially upgrading the S20 Eagle to the S22 Eagle.
Finally, we would like to thank you again for your trust and support of King Song, and appreciate your continued support. We take this incident extremely seriously and will continue to investigate further details of this incident. Meanwhile, we hope all of you will supervise every amendment we make to ensure the healthy development of EUC industry.
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King Song Intell 60, LTD
Apr 2nd, 2022
1020507606
