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."
Interesting. Previous experience of internal soft shorts at the Mallory Battery Co. Of Canada (now Duracell) was to do with a separator change.X rays showed clusters of soft shorts at the base of the cylindrical separator. Certain percentages of HgO (Mercuric Oxide) were allowed in the recovered cathode dust and used in the MnO2 (alkaline) cells. What was happening was that the new separator was drawing oxygen out of the HgO resulting in microscopic globules of mercury which bridged between the anode and cathode, Although that experience was with a primary cell perhaps something similar is happening in the Boeing episode...just thoughts.
Apparently, you're right about the high risks of internal shorts, ScotCan. On Thursday, the NTSB announced that the Boeing battery that caught fire in Boston had an internal short in cell number six (of the eight cells). They're still trying to figure out what caused the internal short, though. We've got a story coming up on this in a couple of days.
One photograph shows what looks like a prismatic cell at the end of the burnt out casing. Was this the type used in Boeing's battery? If so these are difficult to cool because of the geometry BUT if a heavy current is drawn the cell temperature rises rapidly but unevenly across the cell. The risk of internal shorts is high in this scenario. Boeing's spokeperson says that the battery management system(BMS) protects against overcharging and discharging, but does not indicate that there is a thermal cut off system to guard against over heating. Is this what is missing? If so modifications to the BMS to protect against overheating would appear to be the answer.
I just had not realized until I watched the NTSB news briefing that there was a question of how the data may have been corrupted by the fire department actions.
It sounded like there may not have been fire present until the fire department opened the battery box.
Apparently in the case of the event in Japan, it was all over by the time the plane landed. The pictures provided by the JTSB show a similar condition of the internals of the battery box but the external conditions seems somewhat more benign.
They do show some nice shots of how the plane was stained by the external venting. I suppose that since the battery lost something on the order of 5Kg of mass there was a lot of Goo being ejected.
This all seemed to be in line with Boeings assertion of how it was all supposed to work. The big departure is that the failure rate in this mode was expected to be much much lower.
I appreciate the need to take care in using the term "fire" and believe you're making an important distinction here. However, NTSB used the word "fire" in its own press release after the teardown of the Logan Airport parts.
The GS-Yuasa battery is just a part of a system. If a part fails is allways not a part trouble is a system trouble. Airbus uses two battery from Saft for the same function.
I thought it might be useful to point out that this all might be much ado about nothing.
In terms of electrical safety, it makes a great deal of difference whether there was fire or just smoke. This may be a fine point that is lost on most folks that are not familiar with electrical safety.
For example, a typical UL safety test will include a test where all safety devices are defeated and the product is evaluated to make sure no FIRE escapes the enclosure during an extreme electrical fault.
Basically the device is destroyed by an electrical surge but it's not allowed to catch anything near it on fire.
A possible key point in the 787 case is the fact that the fire department in Boston mentioned fire. In Japan the report was only smoke. To the layman this might seem like a minor point but to a safety expert it is a big deal.
During the NTSB news conference on 1/24 it was mentioned that the scene was disturbed by the way the fire department removed the battery. Further, apparently the battery enclosure was opened. It made me wonder if there was no fire until the fire department opened the housing. Pure conjecture on my part here.
This also highlights the fact that any sort of cooling system would not normally count in a safety evaluation. It would be shut off just like any other protective measure.
All this talk about the "safety" of various battery technologies is beside the point if the end solution will not cause a fire.
As one with some expecience with safety approvals I thought I would pass this along.
There could be a number of folks included in the list. You might add in Thales, the aerospace company that actually made the battery. Then too are the airlines themselves that installed the replacement batteries. It sounds like some airlines had issues and some did not. Maybe there is a maintenance issue?
However, this 787 battery does not seem to be anything very new. It's very typical that smaller batteries like this do not have complex cooling systems. The companies involved have all sorts of experience with similar batteries.
Yes the Tesla and Volt batteries do have complex cooling systems but they are 10 to 20 times larger and are designed for much heavier duty cycles.
These 787 batteries would seem to be failing at times when they are not even in use! This would make cooling a non issue. Something screwy is going on here.
It has been said here many times already, no one knows what happened at this point. It is totally premature and irresponsible to be making all these rash comments. This is especially true of supposed "Industry Experts".
I think it pretty absurd to believe that the manufacturers did not understand what needed to be done. The question at hand is what happened. I'm sure we will all find out in due time.
Seems like Boeings only fault lies with trusting the battery maker GS-Yuasa. GS Yuasa was responsible for ensuring that the enclosure had proper cooling. Are we to believe that GS-Yuasa's engineers did not know that these cells packed together would get hot? How can GSYuasa possibly claim to be "experienced" when they let this inadaquate cooling slip by? Everyone else using Li-ion batteries seems to know this. Tesla knows this. Chevy knows this. How come GS Yuasa didn't know this?
Cramming into a box is the exact opposite of what Tesla did. They gave up a lot of space for cooling and monitoring of the batteries as well as making sure that an individual cell failure (thermal runaway) would be contained. They didn't engineer with an eye toward totally preventing this scenario, but rather containing the inevitable.
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