FAA Grounds 787s
You can't compare these battery technologies so easily. They are very different.
While NiCd or lead acid batteries simply terminated service when severely mistreated in the way described, LiIon batteries really take it personal.
And respond by throwing flames.
Edit: The Problem is not reverse polarity but overcharging. At about 10% Over -Voltage (corresponds to ~30 - 50% in capacity) it tends to become critical but that varies quite significantly between different cell types..
This is why you normally use balancers for each individual cell.
Overcharging beyond a certain threshold damages the chemistry (the separator becomes electrically conducting) leading to an internal short circuit. Since the separator between the layers is (highly) flammable this will cause ignition of the cell if sufficient energy is stored in the cell, which is the case when fully charged. Self ignition is possible when charged > 40-50% with most Lithium cells (except Lithium Iron Phosphate).
Is it a known fact that they Charge 8 cells in a row without balancer and cut-off?
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Isn't it significant that all of these battery failures seem to take place while the aircraft is on the ground. This would seem to suggest that there is something that happens to this battery when the aircraft is not flying that causes problems. I would think that this "feature" of the failure would go a long way into helping to determine its root cause.
Yes it was but all the others were on the ground. This has been dealt with in previous posts/threads.
In summary, the bat can be used on ground routinely for maint/towing. Discharge & recharge. In normal flight conditions this does not happen.
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In summary, the bat can be used on ground routinely for maint/towing. Discharge & recharge. In normal flight conditions this does not happen.
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NTSB PARTICIPATING IN JAPAN’S INVESTIGATION OF B-787 BATTERY SMOKE EVENT
January 15, 2014
WASHINGTON – The National Transportation Safety Board will participate in the investigation of a smoke event involving the main battery of a Japan Airlines B-787 that occurred while the aircraft was parked at Tokyo’s Narita Airport on Jan. 14.
The investigation is being led by the Japan Civil Aviation Bureau. NTSB aircraft systems investigator Mike Bauer will travel to Japan to assist with the investigation.
All information regarding the investigation will be released by the JCAB.
................
Latest press release.
January 15, 2014
WASHINGTON – The National Transportation Safety Board will participate in the investigation of a smoke event involving the main battery of a Japan Airlines B-787 that occurred while the aircraft was parked at Tokyo’s Narita Airport on Jan. 14.
The investigation is being led by the Japan Civil Aviation Bureau. NTSB aircraft systems investigator Mike Bauer will travel to Japan to assist with the investigation.
All information regarding the investigation will be released by the JCAB.
................
Latest press release.
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Balanced charging is very well established for lithium based batteries and it's very simple to google the specialised chargers used by thousands of people. I've got three of them and each battery comes with a specialised second lead with a connnector reflecting the number of cells to be balanced
Rob
Rob
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This may or may not be true for lithium batteries, but it is NOT true for the various lead-acid types! 12, 24, 32, 36, 48, 72, and 120 volt battery banks made from lead-acid cells are charged in series all the time. I personally used to connect the 24 volt generator to 727s and 737s back in the day and those batteries had no cell-by-cell charger. AFAIK I never burned up an airplane or if I did it burned up after I went home 
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Rob -- Yes, that's true but the reverse polarity and 'all technology' comments are totally wrong. The real point is that this is not such new technology and problems have been in the field for a long time, in non-aviation applications. Knowing how much testing goes into aircraft components, these battery systems must have been cycled hundreds of thousands of times during development (not each battery, of course!). Knowing that the survival of the entire type could be in jeopardy they must have looked as all possible reasons, and this will have been overseen by senior engineers, specialists in the field of batteries and charging systems. If I was Boeing I'd be spending 30% of the investigation on the possibilities of sabotage - don't know how, where or when but it has to be a possibility.
Otherwise:
Note that the problems have been on the ground where risk to life and health is lower - a saboteur might draw the line at that. Otherwise, batteries will usually draw the highest charging current when charging starts and rapidly fall-off (though high-charge rate designs often charge to a maximum internal temperature rather than simply terminal volts). If the batteries are fully-charged the charging current is usually low.
Is there a large load in the powered-down condition? When cleaners and maintenance are on board?
Otherwise:
Note that the problems have been on the ground where risk to life and health is lower - a saboteur might draw the line at that. Otherwise, batteries will usually draw the highest charging current when charging starts and rapidly fall-off (though high-charge rate designs often charge to a maximum internal temperature rather than simply terminal volts). If the batteries are fully-charged the charging current is usually low.
Is there a large load in the powered-down condition? When cleaners and maintenance are on board?
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Island Airphoto said
The differences are pretty simple.
Lead Acid and NiCd cells (even sealed ones) can tolerate a certain amount of overcharge without damage, as long as the rate and temperature are limited.
NiMH can also tolerate some overcharge, but the end of charge point for fast charging gives only subtle warnings.
As long as individual cells are capable of accepting overcharge, it is possible to balance a series string by a controlled overcharge (equalization) cycle which will assure that even the largest capacity cells in the string can be brought to full charge by overcharging the lower capacity cells.
Then if an over discharge takes place, there will only be major cell damage if a low capacity cell is actually reversed. That can be prevented by a clamp or shunt diode.
Thermal runaway can happen in those types of cells if fixed voltage charging without temperature sensing it used, but it does not happen with a good charger on a series string unless one cell or battery gets much hotter than the rest or the whole string gets out of control.
But there are two characteristics of most lithium chemistry batteries that require more active balancing systems:
1. lithium cells will not tolerate prolonged overcharge the way lead acid or NiCd will.
2. When a lithium cell (any lithium chemistry) is discharged below a certain voltage (dependent on the chemistry, but greater than 2 volts) it is permanently drained and cannot be recharged under any combination of applied voltage. If you try to recharge such a cell, it will enter a hazardous state long before its voltage reaches the normal charging cutoff voltage. That means that some sort of balancing and protective circuitry at the cell level is mandatory for safe series discharge and charging.
This may or may not be true for lithium batteries, but it is NOT true for the various lead-acid types! 12, 24, 32, 36, 48, 72, and 120 volt battery banks made from lead-acid cells are charged in series all the time. I personally used to connect the 24 volt generator to 727s and 737s back in the day and those batteries had no cell-by-cell charger. AFAIK I never burned up an airplane or if I did it burned up after I went home 
Lead Acid and NiCd cells (even sealed ones) can tolerate a certain amount of overcharge without damage, as long as the rate and temperature are limited.
NiMH can also tolerate some overcharge, but the end of charge point for fast charging gives only subtle warnings.
As long as individual cells are capable of accepting overcharge, it is possible to balance a series string by a controlled overcharge (equalization) cycle which will assure that even the largest capacity cells in the string can be brought to full charge by overcharging the lower capacity cells.
Then if an over discharge takes place, there will only be major cell damage if a low capacity cell is actually reversed. That can be prevented by a clamp or shunt diode.
Thermal runaway can happen in those types of cells if fixed voltage charging without temperature sensing it used, but it does not happen with a good charger on a series string unless one cell or battery gets much hotter than the rest or the whole string gets out of control.
But there are two characteristics of most lithium chemistry batteries that require more active balancing systems:
1. lithium cells will not tolerate prolonged overcharge the way lead acid or NiCd will.
2. When a lithium cell (any lithium chemistry) is discharged below a certain voltage (dependent on the chemistry, but greater than 2 volts) it is permanently drained and cannot be recharged under any combination of applied voltage. If you try to recharge such a cell, it will enter a hazardous state long before its voltage reaches the normal charging cutoff voltage. That means that some sort of balancing and protective circuitry at the cell level is mandatory for safe series discharge and charging.
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I do not doubt that this is true, but can anyone explain why we have not heard of such problems with lead acid or NiCad systems? There are scads of 24 volt systems of all battery types in aircraft, marine, and ground transportation equipment, all of them having 12 cells in series.
NiCad and NiMH are fairly common, with the NiCad falling out of favour due to the cadmium and the fact that they perform less well than the metal hydride cells. They give about 1.2V/cell, so you'll need 20 of them to get 24V. This is what's been used in aircraft - better energy density than a lead-acid cell, but more expensive. The charging method is different, too. The cells are fairly robust.
Lithium cell technology is a lot more interesting. It is possible to get primary cells (i.e. not rechargeable) and secondary cells (which are). The contents are highly reactive and can catch fire or explode, especially when short-circuited. The common rechargeable cells give a nominal 3.7V/cell so your 24V is going to be either eight or nine cells in series. They're very picky about being charged, the temperature is important, below 0C or above 40C needs care and usually you just don't bother (typical for consumer gadgets such as phones). It's possible to charge at temperatures up to 50C at a lower capacity. If you apply too great a charge voltage (>4.2V/cell, lower at high temperature) then different chemical reactions start occurring and interesting things can happen. They also don't like working at all as you go over 60C. Unlike NiMH batteries, Li-Ion cells are endothermic on charge, so they will cool slightly. The other side of this is that they're exothermic on discharge, so as well as resistive heating, there's some chemical heating going on. If you're not careful you can get metal dendrites growing from one of the electrodes, puncturing the separator between the plates, and then shorting to the other one. This is not good, as it's a dead short across the battery and lots of heat gets generated which can melt things and make it worse, boil the electrolyte to increase the cell pressure and lead to the sort of catastrophic failure that has been seen. The energy density is better than other cells, which is why Boeing are trying to use them. Today I had chance to compare a 3.6AH NiMH battery and a 4.2AH Li-Ion battery of equivalent size and the Li-Ion was noticeably lighter with 16% more capacity.
inetdog has already touched on the difficulties of charging a string of cells in series regardless of chemistry type - inevitably one will reach full charge before the others so you have to deal with that, and it's usually done by attempting to match a group of cells to minimise the differences. Overcharging often results in capacity loss, so next time the problem will be even worse, in a spiral of doom down to cell failure after repeated charge/discharge cycles.
In a previous job I had dealings with lithium C-cell non-rechargeable batteries. They had to be shipped in boxes labelled "not to be transported on passenger aircraft", and the paperwork for DHL/Fedex/UPS to carry them is fairly dire.
Lithium is a really good battery technology until it goes wrong, at which point it gets quite scary.
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Isn't it significant that all of these battery failures seem to take place while the aircraft is on the ground. This would seem to suggest that there is something that happens to this battery when the aircraft is not flying that causes problems.
For that very reason, I would think twice to start the APU in flight, which means discharing the starter battery and re-charge it once the APU is running. So far the issue only happened on ground, where the APU is typically started before the engines are switched off.
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How do they manage to not charge the batteries in the air? Sounds weird, no batteries will maintain it's power level even if they are not used. When i drive my car, I use the battery to start the engine, and the battery is charged constantly from there on, even if it is not used for anything.
How do they manage to not charge the batteries in the air? Sounds weird, no batteries will maintain it's power level even if they are not used. When i drive my car, I use the battery to start the engine, and the battery is charged constantly from there on, even if it is not used for anything.
The 787 (and other a/c) will have a rather more sophisticated charging system than your car.
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Generally speaking the a/c will be on some sort of AC power long before it gets airborne. Either ground power or APU will be AC supply. If the a/c was powered up from 'dead' then the battery will be recharged by one of those sources probably hours before the engines are even started.
The 787 (and other a/c) will have a rather more sophisticated charging system than your car.
The 787 (and other a/c) will have a rather more sophisticated charging system than your car.
But that doesn't mean the batteries are not charged in flight.
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The early ones with liquid acid in them are clearly a risk in aviation and even now, if you want to take such a battery on an aircraft (as part of a wheelchair, etc) you have to make arrangements to drain the acid and leave it behind, then get more at the destination.
Originally Posted by ManaAdaSystem
Quote:
I am well aware of that, and I am also aware of the fact that the airplane batteries are normally not used when AC power is supplied.
But that doesn't mean the batteries are not charged in flight.
I am well aware of that, and I am also aware of the fact that the airplane batteries are normally not used when AC power is supplied.
But that doesn't mean the batteries are not charged in flight.
Yes. But discharged to what level? Since the battery (main) is part of a critical backup system (brakes), there is a requirement to maintain it to some minimum level of charge. Because there are parasitic loads and some level of self discharge, the charge cycle will periodically have to be started. How this is sensed and how this level relates to the charging algorithm could affect the health of the battery.
LiON batteries do not like to be 'float charged' due to the voltage inflection phenomenon (higher state of charge at a given temp results in a lower terminal voltage) and resulting runaway. So it would be expected that the battery/charger system will cycle between full (charger turns off) and some recharge threshold point charger turns back on).
LiON batteries do not like to be 'float charged' due to the voltage inflection phenomenon (higher state of charge at a given temp results in a lower terminal voltage) and resulting runaway. So it would be expected that the battery/charger system will cycle between full (charger turns off) and some recharge threshold point charger turns back on).