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Another good discussion on battery design, Boeing vs. Tesla.
The battery in Tesla's Roadster used thousands of small cobalt cathode lithium cells - same chemistry used in the Boeing battery. Tesla delivered 2,418 Roadsters beginning in 2008, that contained 16,517,358 of these lithium cells. There are roughly 800 lithium cells total in all the 787s Boeing has delivered. No Tesla customer has ever had a burned up battery. Two customer 787 batteries have fried. The Boeing battery contains eight GS Yuasa, LVP-65 lithium cells, each weighing 2.75kg (6 lbs). The much larger Tesla Roadster battery uses 6,831 cells similar to the Panasonic CGR18650HG [page 25], each weighing 42g (1.5oz). The big cells in the Boeing battery are flat, allowing them to be packed tightly against each other. If one of these big cells experiences thermal runaway, a lot of heat is released, and because the cells are touching, adjacent cells will fry, too. Since the eight cells in the Boeing battery are connected in series, there is no practical way to disconnect a faulty cell and still have a working battery. If one cell goes, the whole battery goes - at least it's simple. Because the cells of the Tesla battery are small, if one cell suffers thermal runaway, relatively little energy is released. And since these cells are round, they are not packed as closely together making it much harder for a failed cell to heat up other cells nearby. With many cells making up the Tesla battery, the battery control system is able to disconnect and isolate a faulty cell and the battery will continue working. Complicated, but it doesn't burn-up. |
DType your post 543
Well done you. When it comes to explaining what has gone wrong with a complex system that sort of post is very constructive. I seem to remember a NASA lander that was lost just due to a metric/imperial error. Boeing are particular vulnerable to that sort of problem since they are outsourcing from an essentially imperial world to an essentially metric one. The longer all the very clever people investigating the problem around the world come up with nothing wrong in their part of the overall system the more likely it is in the end to be something too obious to have been considered. |
I believe Lockheed accepted blame for the Mars Climate Orbiter metric/imperial snafu.
They were contracted to produce the output in metric, and failed this task. It wasn't a case of the project specification being faulty and therefore no party to blame. The project specification was correct and stated metric units, but Lockheed appeared to not follow it. |
they are outsourcing from an essentially imperial world to an essentially metric one. You are right though about the need to take a holistic look. Most industrial batteries are constantly under load and therefore to keep them in service they are constantly experiencing charging/discharging cycles. The Li-ion units on the 787 are standby batteries in the true sense of the word ie. they stand doing nothing for pretty much all of their service life only occasionally being called into use. If I was the engineer overseeing this process I would be looking at this and at things such as 'were the batteries that had to be replaced ever used in service'. Used as in had a real load applied such as starting an APU when this couldn't be done from from the on-board gennies or GPU, or did they just sit there in the bays in a constant state of 'charge' with the occasional test. A key part of this is the data which shows how many replacement batteries were from the aft (APU) location or the fwd (main) location. It is the answers to questions such as these that may reveal the problem as much as looking at individual voltage/temp/float charge data. Good luck to them :-) |
SoS
I think you touch on the most important question... The FAA requires a BACK UP electrical supply, for a very short period should all else fail. The Batteries have no chance of pressurizing the Hull, and the requirement is for five minutes of service, roughly enough time to get the humans down to breathable air from flight levels, in an emergency. It is looking more and more like the 787 engineering scheme is to incorporate a back up system into a sustainable part of the in flight regime of systemic electrical supply. If so, they violate the purpose of the regulations from my point of view. At the very least, and I pointed this out long ago, the Yuasa batteries should be round, wound without rectilinear stress on the plate, such that heat can be dissipated, rather than concentrated in the case. For that matter, the case should be cylindrical as well, if only to honor the principle that square batteries create problems, if the plate is rolled. So from the outset, the design appears to challenge best practice, why? Because square "looks" better? |
Hi,
SoS, Duty cycle indeed is important to be considered in the analysis. And APU vs MAIN (batteries) failure comparison. I commented on another possible 787 System "use" of the Thales battery in B/C thread. Lyman, bleed scheme change in 787 created new dependability requirements to a degraded configuration. But as i imagine the POB are not relying on the Li Ion battery. As i understand RAT and MAIN are for other less critical uses. Or not? |
The Australian Civil Aviation Authority recently promulgated a rule banning all batteries, of ANY capacity and ANY chemistry, including Primary (non-rechargeable) batteries from hold baggage. All batteries must be in carry-on luggage, either in their device or packed in an insulating container (paper envelope will do). |
Brilliant BUREAUCRATS have endless "capabilities"
Hi,
Poorjohn: Bureaucrats are "brilliant". Did you hear on 999% safe (or something similar) to 787 return to the skies? |
Sorry did do it today in a fumehood with some Li-Mn seems Ok to put out, Li-Co is deadly, you can always throw you mobile in a river if it catches fire.....
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I think you touch on the most important question... The FAA requires a BACK UP electrical supply, for a very short period should all else fail. The Batteries have no chance of pressurizing the Hull, and the requirement is for five minutes of service, roughly enough time to get the humans down to breathable air from flight levels, in an emergency. It is looking more and more like the 787 engineering scheme is to incorporate a back up system into a sustainable part of the in flight regime of systemic electrical supply. If so, they violate the purpose of the regulations from my point of view. The Main Battery is there to ensure continuity to certain systems in the event of total electrical failure (Engines out for example) until the backup systems kick in IE. RAT/APU. In addition because the brakes are electric, there needs to be a store of power to bring the a/c to a stop after a succesful emergency landing. The RAT will be of no use as airspeed drops on roll out so the battery power is used. To put it into comparison with the 777. The APU has electrical and pneumatic starters, so even if electrics is lost, bleed air will start the APU, The Battery is still there to keep standby instruments going of course until the RAT drops and powers up. As for the brakes, hydraulic back up is from an accumulator (compressed gas). |
Why the fixation with Lithium?
Why is there such a fixation with Lithium? Does it really matter what battery technology is used provided it works reliably and does not burst into flames at random intervals?
Suspect that in something weighing over half a million pounds they could have used lead acid (ancient, reliable, tried, tested and not prone to catching fire) in which case Dreamliners might still be in service. Not that I'm suggesting this would be the best choice but it does illustrate the point. If every Lithium battery is to be attended by a large tank of water the weight advantages will soon disappear. |
It doesn't have to be lead-acid
NiCd and NiMh do a good job. Reliable, safe, cheap.... |
...but doesn't provide as much energy per kilo per cubic metre. :-)
Are the electrical specifications for the 787 in the public domain yet? SoS |
Also LiIon is doing a good an save job. How many mobile devices are out there powered with those? Mobile Phones, Laptops, Playstations, Shavers, Cameras, Watches, ... - a huge amount of LiIon-Systems works perfect. How many case came up with some issues? 20 out of 1.000.000.000?
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@Taunusflyer
It isn't that simple... As long there is just one cell (3.7 Volts) it's not rocket science. If the voltage demand is higher, e.g. 28 Volts, you need 8 cells. And there is the challenge. They have to be charged (on 787 serial) AND balanced AND monitored. If this is not properly done, a thermal runaway may occure. |
Back to basics
It's time to get back to basics; what are Boeing going to DO? What are their options?
There are few things more serious than an in-flight fire, however supposedly contained or containable. The current batteries have demonstrated an unacceptable risk of such, and not by a small margin. If Boeing want to continue using the existing technology, they're going to have an uphill battle proving it safe; this will not be quick, cheap, or easy. If they decide to switch to a different technology... well that's a whole different ball game. Any other battery technology will not have the same energy density; they won't be able to fit alternative technology batteries with equivalent capacity in the same *space*. So not only would switching to a different battery technology entail a complete redesign of the charging and monitoring systems, it would require structural reengineering of the equipment bays to fit larger batteries. Neither of these options are going to be quick. This aircraft isn't going anywhere any time soon. Not this year, maybe even not next. (I'm no electrical engineer and neither are most of you - but engineers I know and trust have the same opinion) |
Whew...
I am soo glad that the batteries are the only new technology we have to be concerned with....:eek: |
If they'd gone with Li-Mn there would have none of this fiasco, going with Li-Co must purely down to cost, not weight or space.
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This aircraft isn't going anywhere any time soon. Not this year, maybe even not next. No Quick Fix In Sight For 787 Almost three weeks into its investigation,......hasn't found the root cause of the lithium-ion battery fires ......... Japan's Transport Ministry said investigators found no problems at GS Yuasa, ......... Meanwhile, a financial analysis by Jefferies & Co. found the grounding will likely cost Boeing more than $500 million, and in a worst-case scenario, up to $5 billion, according to Bloomberg. ............ On Wednesday, Boeing CEO Jim McNerney is expected to speak publicly about the airplane's problems for the first time, when he unveils the company's latest financial report. |
No "CRM" in BA board?
Hi,
ExSp33db1rd, A wrongly selected battery (from a single supplier) could do this damage? "CRM" inside BA cockpit must have altn. options (technically speaking, on batt. issue) to shorten the grounding. Or the FAA review is the real problem? (Wrong battery selection yet represented an organizational and technical error. Now the delay in finding WHAT and WHY the batteries didnīt perform is going to damage a very important value: CONFIDENCE) Is it possible? |
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