Kingsong S20 Cut Out Fire Investigation (New York) - What happened?

[U-Stride]

Here is what lead up to the KS20 FIRE 🔥 

The goal was to feel out the KS20 initially. Once I got a good feel for the wheel next was to stress it out a bit by riding similar to how I ride my gotway wheels on a good hard riding day. Please see below for the step by step events as to what happened pre-fire. I will attempt to create a very short video step step that illustratates how to repeat this scenario to hopefully add some clarity as to what really happened.

Start

1. I made several successive Hard accelerations with minor to hard braking initially to feel out the motors power delivery 

2. Hard acceleration but gradual still with some torquing 

3. 1st Hard braking attempt at high speed where I felt the motor slipping. I then let off so it catches itself 

4. About 2 seconds after it catches itself I attempt another hard braking at speed where the motor slipped again and right after the 2nd slip, I felt/heard a loud pop. 

5. The wheel looses balancing ability 

6. While on it's side the wheel shakes jittery like 

7. Few seconds later sound of seething 

8. Smoke appears 

9. Explosion of fire

Edited March 30, 2022 by U-Stride

[MetricUSA]

Lesson so far...it is not a 65 km/h wheel as is, and the wheel probably would not started on fire if you quickly went to the legal speed of 40 km/h and braked hard....

[Tawpie]

1 hour ago, MetricUSA said:

Lesson so far...it is not a 65 km/h wheel as is, and the wheel probably would not started on fire if you quickly went to the legal speed of 40 km/h and braked hard....

You lost me here... it looked to me like U-Stride was going pretty slowly (at the end). And others that didn't kill the controller and didn't have the wheel catch on fire have been going 70 kph... didn't SpeedFeet say he was doing well over 60 for a half hour?

Edited April 1, 2022 by Tawpie

[NErider]

Another factor may be due to previous use/crashes. As noted in other disassembly vids, the battery packs aren't really robustly protected. They are slid into the aluminum case. So if the case takes a hit from a crash, the battery pack and BMS takes a hit as well. 

Personally, I think it may be a couple of things that lead up to the failure and fire. Torquing it likely pushed it over the edge and now we may never know because it was burnt to smithereens. Lol. 

 

[Tawpie]

the report just posted https://www.kingsong.com/kingsongnotifications.html#images-1

[BatteryMooch]

Thank you for posting that @Tawpie!

Wow, depressing to see so many software and hardware failures at work here. IMO all of these issues should have been found early in the bench testing. Especially with them being so easy to identify now.

Some thoughts…

• Intermittent/repeating short circuits like these should be expected (eventually, though rarely) in a high vibration environment and the BMS/ESC/pack tested to make sure these types of short circuits are not a problem.
• The fuse not blowing is huge…HUGE. This component must be properly spec’d to prevent exactly this kind of unexpected fire hazard. 
• Increasing the thickness of the nickel strip they use would make pack assembly a bit tougher, and a touch more expensive, but would give the fuse more time to blow before the heat from the nickel strip forced some cells in the pack to go into thermal runaway (catch fire).
• They didn’t mention any hardware changes/fixes though they might be waiting for the pack/BMS analysis to be done. IMO they won’t be able to say anything definitively though about the cause after this analysis due to the damage. Best to just design a much more robust system than they have now and actually TEST it.

Looking forward to KS sorting it all out though and a more robust S22 coming to market!

Edited April 2, 2022 by BatteryMooch