Questions about the cooling of the Boeing 787's batteries came up again this week, as Tesla Motors CEO Elon Musk publicly stated that the plane's large pack design is a risky one.
"Unfortunately, the pack architecture supplied to Boeing is inherently unsafe," he wrote in an email to Flightglobal.com. "Large cells without enough space between them to isolate against the cell-to-cell thermal domino effect means it is simply a matter of time before there are more incidents of this nature."
Tesla uses lithium-ion battery packs in its Tesla Roadster and Tesla Model S vehicles. Its design involves 6,000-7,000 small lithium-ion cells. Musk told Flightglobal that the cells are separated in a way that makes them less likely than large cells to suffer from thermal runaway events.
Elon Musk of Tesla and SpaceX: "Unfortunately, the pack architecture supplied to Boeing is inherently unsafe." (Source: revengeoftheelectriccar.com)
Musk has tweeted his desire to help Boeing with its battery problems, which included incidents in two Japan Airlines flights and a United flight this month. On Jan. 18, he wrote, "Maybe already under control, but Tesla and SpaceX are happy to help with the 787 lithium ion batteries." A few days ago, he followed up: "Desire to help Boeing is real & am corresponding w 787 chief engineer." Shanna Hendriks, a spokeswoman for Tesla Motors, confirmed to us that Musk made the comments on his Twitter account and by email to Flightglobal.
Marc Birtel, a Boeing spokesman, would not verify whether his company's chief engineer has been in contact with Musk. "We're engaged with a number of experts both inside and outside the company," he told us, but Boeing is "not identifying them by name publicly."
The issue of battery cooling has been at the forefront of the Boeing story for a week. Donald Sadoway, the John F. Elliott professor of materials chemistry at MIT who is involved in a battery startup with Bill Gates, told us last week that a forced air cooling system and sensors may be needed to monitor and cool the battery in the event of overheating. Elton Cairns, a professor of chemical and biomolecular engineering at the University of California, Berkeley, and a fuel cell designer for NASA's Gemini spaceflights, also suggested that an air- or liquid-cooled system would be necessary.
Even at low temperatures, the Boeing system could still have been at risk, according to Cairns. "When the plane is at altitude, the air is less dense," he told us. "So even if it's cooler, the less dense air may not have adequate heating capacity to provide enough cooling for the battery. If they don't have active cooling, then I question the adequacy of the cooling arrangement."
Boeing uses eight lithium cobalt oxide cells in its battery packs. According to experts, the cobalt oxide chemistry is known to have higher energy densities than other forms of lithium-ion, so it needs an active cooling system.
Boeing representatives told us that they are not aware of an active cooling system for the 787 batteries. "Obviously, there were multiple backups associated with the battery to ensure the system was safe against overcharging and overdischarging," Birtel said. "But there was not a specific cooling system associated with the battery."
Cairns called battery management ICs (to monitor voltage and current) an important part of a safe pack, but he also said energetic batteries often need more than that.
"The electrical system that manages the battery is not a complete battery management system," he said. "In my view, a complete battery management system includes the dispersion of any heat that is generated by the operation of the battery. Just having protective circuits is fine, but it is absolutely insufficient."
Lighten up on Tesla. My money is on ANYONE ( I don't care if it's Black and Decker) with several years of experience with tens of thousands of cells in the market place vs. all the computer modeling in the world. I doubt that the computer models on any of the newer technologies are much good at this point.
The manufacturer of the cells is only responsible for the cells if they didn't build the entire battery.
Tesla crammed 6,800 laptop cells into a box with minimal monitoring. They blatantly ignored the manufacturers general recommendations.
They may well have gotten someone to agree to this but the point is that the Tesla design was very seat of the pants and not generally condoned. It was then hailed as a breakthrough.
Some breakthrough. Break all the rules and build a big bomb then hail this as some fantastic feat. I call it irresponsible grandstanding. Maybe its OK for a one off sports car but certainly not an airliner.
I find it very difficult to believe Boeing did not test to discover all of the failure modes possible with this battery system. I feel they must have and I would love to see a chronology of those tests and the pass/fail results. I don't suspect they will be published but it would be very enlightening. I think it would be prudent to explore all resources, including TESLA, when trying to find solutions to this problem.
To say Tesla has no right to talk about battery because they use commercial grade while Boeing used aviation grade battery is absurd. A battery is a battery no matter what grade it is. Fundamental principles are the same. In many case, avaition grade just means there are paper work and trace to go with the product. In many case, there are no difference in quality. That is why you see the trend in military and aviation going to COTS (commercial off the shelf) whenever possible to save money.
I appreciate Tesla's reasoning. The Batteries require space and channel cooling which will makes them to heavy for airborne equipment. Fact is the battery sensors did not respond is an issue. Since they proved to function then I assume the rapid heating cause the batteries to burst before the sensors detected the problem. Again these batteries need to be enviromentally screen in airborne mil-STDs to see if they can survive high altitude conditions with jet engine vibration. Since they failed too soon in life expectancy this indicates a problem.
Litium batteries are not properly built for space enviroment at this time. They have inherit mechanical design flaws that cause premature failures. in laptops, phones, cameras, now planes.
Ah it's the sheet metal case that apparently kept all the burning pieces inside. According to Boeing there is also a ventalation system to remove any smoke or fumes.
To me this is some level of evidence that Boeing forsaw this sort of failure. It looks to me like the thing got too hot and the safety systems did thier job.
The point is that Lithium batteries don't require active cooling. They require not getting too hot.
The main reason that active cooling is used is not to cool them while in a failure mode it is to keep them from failing in the first place. In a low load application this can easily be done with no cooling at all.
Adding cooling could be an additional safety risk in itself since it would greatly increase the complexity.
Actually if you recall it was the cooling system that caused the fire in the Volt battery pack!
going down mainly wrong tracks. There a number of potential problem sources, which could account for the failures. There are no guarantees that there are simple fixes. Prior comment about inbred, NIH. Based on my many decades of engineering involvement, I would like to presnet my list. I do not think Boeing should get a free ride, but a modest recompense, public thanks (technical acknowledgement) should suffice. Sannerwind@gmail.com JR/ CEO
Having seen dozens of pictures of the battery box, I cannot find any evidence of a physical containment system beyond the sheetmetal case. As lithium batteries are charged, they will physically swell slightly as they approach 90%+ SOC. Uncontained, each charge-discharge cycle slightly degrades internal structures through mechanical action. A prudent design will incorporate structural plates on either end of the battery stack connected with tensioned fasteners, preventing the physical distortion of the battery case by the internal components. '
The failure mode matches this model. Repeated charging slowly degreades the internal structures until an internal short is developed. The short would only be manifested upon charging as the battery once again flexes as it aproaches 100% SOC. The same situation likely occured during the development of the charger when an "event" burned down the development facility.
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