When he looked at photographs of the 787s lithium-ion battery, he saw that it is actually eight notebook sized batteries all packed next to each other in a closed box. This means that only the batteries on the ends have any hope of venting the heat they generate. The other six batteries just heat each other up since they can’t release their heat outside the box.
Sadoway did not have access to investigators’ details, however, based on what he saw, he urged Boeing to create vents within the box so the batteries could dissipate heat.
He also argued that Boeing should put temperature sensors on each of the eight batteries and implement a “system of forced airflow” inside the box to help assure that the temperature of each battery would stay below a threshold level.
Sadoway estimated that these changes to the design of the lithium-ion battery would add to its cost. Instead of $1,000 per battery, the cost might rise to $2,000. But that cost would be “peanuts” compared to the $207 million retail price of the 787.
And reports out Thursday suggest that Boeing engineers are thinking about a redesign of the 787s lithium-ion batteries that appear to reflect Sadoway’s ideas.
For example, The Wall Street Journal reports that Boeing is “looking at increasing the separation between cells in the lithium-ion batteries to reduce the potential hazards from heat or fire spreading within the batteries and adding enhanced heat-sensors.”
These ideas are consistent with Sadoway’s approach. For example, physically separating each of the cells would make it easier to vent the heat that each one generates. And the idea of enhanced heat sensors could mean that Boeing could implement a battery control system that would sense if the cells’ temperature was rising above a threshold level and take action to stop the batteries for burning up.
The Journal also reports that Boeing is also “considering ways to keep cells more rigid, preventing them from shifting under certain conditions and interfering with electronics.”
And a report from Thursday’s New York Times suggests that Boeing is working on working “more solid containment cases and better venting mechanisms in the event of overheating.” This sounds like an improvement. However, unless Boeing can stop the problem of thermal runaway – a chemical reaction in which a rising temperature causes progressively hotter temperatures — the 787s will not be safe.
But the Times reports that Boeing has a Plan B — tasking engineers to use more conventional batteries in case regulators banned the lithium-ion ones. And the alternatives they consider should include the one that Sadoway recommended — a safer, but less powerful Nickel Metal Hydride (NiMH) battery.
Sadoway reckoned that this NiMH battery would have to be 50% heavier — perhaps 37 more pounds — representing 0.01% of the 787s 502,500 pound weight in order to deliver sufficient current to the 787.
As Sadoway suggested, using a new battery would require Boeing to order Thales, the French company that makes the 787s electrical system part of which controls the lithium-ion battery, to develop a new control system that would work for the NiMH battery. Sadoway thinks that could take a year to design, build, test, and make safe to fly. Based on Sadoway’s insights on the 787 battery, perhaps he should be heading up the team that is working on this problem.
However, it is easier to solve the technical problem of how to power the 787 than it is to change the actions and culture of Boeing — the company that managed to convince regulators and customers that its flawed lithium-ion batteries made the 787 safe to fly."