On Friday afternoon just before 4PM we received notice that one of the EWABI electric bamboo bike battery packs had caught on fire. Nobody was hurt.
In the interest of public safety and transparency we are going to use this as an opportunity to explain reasons for this failure, safety precautions that both riders and e-bike builders can take to minimize the risk of this type of event and finally to explain the steps we have taken in the last two days.
Noan Fesnoux, a teacher at the Green School and an EWABI Electric Bamboo Bike Club member was riding his bike along a flat section through rice fields not far from Sibang Gede Market. He heard a pop and thought that the tire had blown. When he looked down he noticed some smoke coming out of the battery pack. Fortunately Noan knew that smoke and batteries are a very dangerous combination and immediately dismounted the bike and ran to safety. The pack then caught on fire which spread from one cell to the next with a series of pops. The picture above is at the peak of the fire.
Noan immediately contacted EWABI and we dispatched a team to the site to assist him. Shortly thereafter we began an immediate recall of all EWABI electric bikes. An email was sent at 4:27 PM (June 16, 2017 EWABI Electric Bamboo Bike Recall Notice) followed up by individual phone calls and texts to reach each rider and instruct them to not ride the bike. We were able to reach all but two of our members by 6PM and then began to plan for the pickup of all bikes. We also started to organize a team for the next day’s investigation of the bike that had caught on fire.
For a battery to catch fire is rare. According to the Electric Bike Report there are over 220 million electric bikes in daily service around the globe and fires are so rare as to attract international attention. Their article entitled Electric Bike Battery Fires and How to Prevent Them [VIDEO] provides a great set of tips and guidelines for both riders and builders.
In this particular case the electric bamboo mountain bike was powered by a Lithium Ion battery pack using Sanyo NCR18650GA 3500 mAH 10A MH12210 cells and assembled by E-Bike Jakarta. It had a DC MOTO controller and BMS. More details on the exact specifications and also our investigation notes can be seen at June 16, 2017 Battery Pack Fire.
Based upon the June 17 review of the burnt remains of the battery pack we determined that the pack had been poorly assembled and that our own receiving and inspection protocols for purchasing battery packs was inadequate. The specific issues regarding the assembly of this battery pack were…
- Nickel plated steel strips were used to connect the cells instead of pure nickel which can handle much higher temperatures. Nickel plated steel could still be ok if it is in sufficient quantity and properly assembled but it was not.
- For this type of pack there should be 4 connections between each series. We opened up a battery pack that came from the same batch as the one that burned and found there were only two or three connections between series and in some cases due to faulty soldering there was only one.
- A BMS from another similar pack exhibited some heat damage and we are still trying to determine if this was another contributing factor.
- The assembled battery pack was placed into a soft bag without adequate padding and stabilization which could have led to excess motion that could have loosened the already weak solder points and impacted the integrity of the internal wiring.
We believe that these factors led to a hot spot that ultimately shorted out a cell that then caught on fire and spread to the remainder of the cells.
Micah Toll who is an expert on Lithium Ion battery pack assembly remotely assisted our local team in our investigation.
By the end of the day on Saturday June 17 we had retrieved all but one of the EWABI electric bamboo bikes that were in the field. We are now planning to go one-by-one through each of the bikes to conduct a rigorous inspection of each battery pack based upon our new safety standards and inspection protocols.
There are inherent risks with any product that is powered by a battery. That being said there many ways to minimize those risks and at EWABI we are committed to doing everything we can to provide the safest electric bikes possible. We are also committed to transparency and hope that this initial report helps riders and builders to better understand some of these risks and steps they can take to avoid a situation like this.
We are in the process of recruiting additional electrical engineering talent. If you know of anyone in Bali that has this background and is interested in getting involved please send us their info at firstname.lastname@example.org. We are also coordinating with experts around the globe and appreciate any introductions you can make to individuals or organizations that can help us to create the safest electric bikes possible.
Peace & Love
Mark & team EWABI