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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 8th Mar 2013, 20:59
  #881 (permalink)  
 
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Hi mm43,
"The APU once online should be self sufficient, and not beholden to the state of APU battery"

If the APU and/or its 2 gennies (starter/generators) fail, perhaps catastrophically, there must remain a power supply to control the APU shutdown, and trigger the fire bottle(s) if necessary. The APU may have a FADEC generating its own power during normal running, but the APU also needs some kind of battery back-up, IMO. (Must admit I'm "winging" this one!)
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Old 8th Mar 2013, 21:19
  #882 (permalink)  
 
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@Lyman
Did Boeing replace three batteries per fleet unit without knowing the cause for failure? That would be most troubling.

But if they knew the cause, how is it NTSB does not know it? Even more troubling….
In the absence of external ground power, the 787 Ship's Battery can provide power for functions including refueling the plane or operating the brakes during towing. The APU battery can provide power for functions like running / anti-collision lights during towing.

Almost all of the battery failures were caused by ground personnel running these functions off the batteries for longer than Boeing's guidelines called for. This caused the batteries to discharge to a state that tripped safety systems to prevent over-discharge and/or damage to the battery. Said batteries were removed from the plane, re-charged at the airline's maintenance facility or an appropriate MRO, and then returned to service.

@inetdog
According to the description in the report, the controls for the APU are powered only from the APU battery bus.

The battery bus might also be powered from the charger (BCU) if the battery goes open circuit, but apparently when the battery fails in a short circuit mode or high enough level fault alarms go off the battery bus cannot receive external power and so the APU cannot run.
This is evidently a Boeing design philosophy. I have been informed that the 777's APU will also shut down if the APU battery fails and on the 767, turning the APU battery switch to the off position while on the ground will shut down the APU.
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Old 8th Mar 2013, 21:20
  #883 (permalink)  
 
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The proposal by Boeing was that only overcharging would cause a fire....

Fire is required to be 10^-9 as a safety critical factor.

So I would not want my batteries charging during flight, that makes the regulations not pertinent. Fire on the ground is calculated to different parameters.

I also would not want to use these batteries under casual circumstance....

That is why quick charging is a requirement, the minimum V must be met prior to launch, not anytime after....

It also explains why Boeing initially pooh poohed the smoke in cabin aspect of the fire. "Inflight, the cabin Pressure prevents it..."

Pretty slick.

And why spontaneous ignition was allowed to be considered impossible by FAA.

I say dis-establish this rubber stamp agency, pronto.....

Or require Congress to speak forensic linguistics.....
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Old 8th Mar 2013, 21:26
  #884 (permalink)  
 
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kiskaloo...

Almost all of the battery failures were caused by ground personnel running these functions off the batteries for longer than Boeing's guidelines called for. This caused the batteries to discharge to a state that tripped safety systems to prevent over-discharge and/or damage to the battery. Said batteries were removed from the plane, re-charged at the airline's maintenance facility or an appropriate MRO, and then returned to service.
Can you cite a source?

Also, once discharged, these batteries cannot be "recharged" according to Boeing...and Yuasa. There is no "return to service". My belief is that once discharged, the presence of dendrites makes them useless. And potentially dangerous.

Were the accident batteries in the "replacement group"?

Which frankly does not sound reasonable, just set the baseline charge state higher than FAIL. Let the lights go dark, ffs.

This is evidently a Boeing design philosophy. I have been informed that the 777's APU will also shut down if the APU battery fails and on the 767, turning the APU battery switch to the off position while on the ground will shut down the APU.
The introduction of Lithium Ion Batteries seems to have inspired another look at this "design philosophy"?

Last edited by Lyman; 8th Mar 2013 at 21:36.
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Old 8th Mar 2013, 21:38
  #885 (permalink)  
 
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Chris Scott:
Was it fully charged on APU shutdown at NRT? Does recharging continue from the main electrical system? If not, presumably it would have leaked some of its charge during the 12-hour flight, but not much.
I cannot see the logic in limiting the power to the APU BCU to come only from the APU itself. At a minimum it would have to be rechargeable from shore power, and there would be no reason not to also power it from one of the general AC power busses.

In the Narita incident, it was admitted that there was some sort of unintended cross connect between the APU battery bus and other loads including the entertainment system. Whether that included any possibility of sneak charging around the BCU has not been mentioned, but the diode between the APU battery and the APU battery bus should have prevented that.
Single Point Of Failure anyone?
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Old 8th Mar 2013, 21:43
  #886 (permalink)  
 
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just set the baseline charge state higher than FAIL
exactly, why, if it is such an issue, would you design a system that allowed this to happen?

It is very easy to set the limit above fail, and have it simply shut down, not run itself into the ground...

I think there is much more to this than we have been allowed to know....
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Old 8th Mar 2013, 21:53
  #887 (permalink)  
 
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Chris Scott:

If the APU and/or its 2 gennies (starter/generators) fail, perhaps catastrophically, there must remain a power supply to control the APU shutdown, and trigger the fire bottle(s) if necessary
Which also makes it interesting to see that the battery failure "triggered an APU shutdown". Possibly once the fuel was cut off, the fully functional APU managed to generate enough power while coasting down to complete any required sequence. There was no other power source on the plane at the time, but it does sound like the shutdown would have occurred regardless of what other power was available.
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Old 8th Mar 2013, 22:18
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@Lyman
Also, once discharged, these batteries cannot be "recharged" according to Boeing...and Yuasa.
They cannot be recharged aboard the airplane. They can be recharged on the bench. This information comes from 787 Electrical Engineers with direct knowledge of the procedures.

Were the accident batteries in the "replacement group"?
JA829J's would not have been as the airframe had just been delivered, so it had the APU battery installed at the factory.

JA804A did have it's Ship's Battery replaced in October 2012, but as to whether it was a reconditioned battery, I cannot say.

Can you cite a source?
At least 100 batteries failed on 787 fleet | Business & Technology | The Seattle Times

Most of the batteries were returned because they had run down so far that a low-voltage cutout was activated.
The person on the 787 program with knowledge of the problems said that the electrical-system design makes it commonplace for airline mechanics to inadvertently run the lithium-ion batteries down too low.
Because lithium-ion batteries can be dangerously volatile if undercharged, as well as when overcharged, an automatic cutoff is built into the 787 batteries so that if the charge falls below 15 percent of full, the battery locks.
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Old 8th Mar 2013, 22:35
  #889 (permalink)  
 
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Hi kiskaloo...

from the article you cite...

More than 100 of the lithium-ion batteries have failed and had to be returned to the Japanese manufacturer, according to a person inside the 787 program with direct knowledge.
my bold...

That would not be for recharging right? In other parts of the article

Because lithium-ion batteries can be dangerously volatile if undercharged, as well as when overcharged, an automatic cutoff is built into the 787 batteries so that if the charge falls below 15 percent of full, the battery locks.
So all the dead 787 batteries have been shipped back to Japan and replacements have had to be sent from there.
Pretty expensive charge, shipping, sole source tariffs, down time.

I still think, from reading the Exponent analysis, that Yuasa batteries, perhaps all batteries of this type, plate metallic Lithium at the Anode, when discharging even above 15% of FULL SOC. Is there even an industry standard? If the flow is discharge, does the dendrite process ennable even at 100% SOC?

One battery, in a series of eight, FAILS the Back Up utility of the system, by regulation, and the reliability issue steps in front of the fire.

Replacing 150 batteries for non performing reliability is more an issue than the occasional fire.

Sounds crazy, but fire is not really the fatal flaw.

Last edited by Lyman; 8th Mar 2013 at 22:41.
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Old 8th Mar 2013, 22:38
  #890 (permalink)  
 
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They cannot be recharged aboard the airplane. They can be recharged on the bench. This information comes from 787 Electrical Engineers with direct knowledge of the procedures.
According to the information, over 150 batteries have been sent back to Yuasa, because once they hit that point, the system will not allow it to be re-charged.

It goes further to say that the cost is $16K per cell...

Whos bench, YUASA's...how convienent...

If you have a direct connection with the EE at Boeing, ask them why they designed such an F'd Up system....

The A350 will be flying before the B787 will....

Last edited by FlightPathOBN; 8th Mar 2013 at 22:40.
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Old 8th Mar 2013, 22:42
  #891 (permalink)  
 
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The Main Battery in JAL is not strictly speaking an exemplar, it is involved in the circuitry intrinsically.
Erm, how so?

The Main battery and APU battery circuits are (supposed) to be completely independent.
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Old 8th Mar 2013, 22:52
  #892 (permalink)  
 
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TURIN

Forensically, an exemplar represents baseline, undisturbed, unperturbed. It is not best practice to use a specimen involved in the accident in any way, it could color the results of any and all testing.

And, as we see, the ANA MAIN ship and APU had at least a "tickle" of incestuous commonality.

QED
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Old 8th Mar 2013, 23:40
  #893 (permalink)  
 
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1021:01 APU battery bus voltage decreased from 32 to 31 volts.
1021:04 APU battery current increased to between 44 and 45 amperes for 4 seconds, indicating current flowing into the battery.
My reading of this is that the battery might have been charging when the voltage suddenly dropped a bit. If the voltage dropped due to a partial short circuit in a cell that would probably result in the charge current increasing.

Initially the voltage only falls 1V which is probably not enough for the BMU to see it as a fault (The battery voltage might vary that much due to normal load variation?). That might explain why it continues charging for another few seconds. Only when the voltage has fallen far enough does it realise there is a battery fault and issue the EICAS message.

The way the voltage fall sounds like one cell in trouble because it's dropped roughly one cell voltage (eg 4V).

The strange thing is that the system knew the battery had failed (EICAS message) but the contactor hadn't been commanded to disconnect the battery from the aircraft.

I notice the battery voltage falls to 0V and returns to 28V. I wonder if that was caused by the contactor trying to disconnect the battery? I hope the board controlling the contactor doesn't need a functioning battery to provide power to control the contactor?

Edit: It would be interesting to replace a cell with a box of electronics that simulates a cell. See what happens if you just slowly turn down the voltage of this dummy "cell".

Last edited by cwatters; 8th Mar 2013 at 23:42.
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Old 8th Mar 2013, 23:53
  #894 (permalink)  
 
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The person on the 787 program with knowledge of the problems said that the electrical-system design makes it commonplace for airline mechanics to inadvertently run the lithium-ion batteries down too low.
Because lithium-ion batteries can be dangerously volatile if undercharged, as well as when overcharged, an automatic cutoff is built into the 787 batteries so that if the charge falls below 15 percent of full, the battery locks.
That's all sensible but I wondered why they don't have two low voltage trips? For example if they had one set to say 20% that would prevent the battery getting low enough that it has to be replaced. Instead it would just need someone to apply ground power, start the APU and "press reset".... or have I missed something?

Obviously you would still need to retain the 15% trip for safety reasons.
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Old 8th Mar 2013, 23:59
  #895 (permalink)  
 
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cwatters:
Initially the voltage only falls 1V which is probably not enough for the BMU to see it as a fault (The battery voltage might vary that much due to normal load variation?). That might explain why it continues charging for another few seconds. Only when the voltage has fallen far enough does it realise there is a battery fault and issue the EICAS message.
If the battery was charging at all, then the BCU would have seen current going into the battery. Hopefully one of the things it was looking at was the reading from the Hall Effect current sensor which is directly on one of the battery leads on the battery side of the BCU connection. And if it was checking frequently enough, it would have seen the voltage drop happen while the net current into the battery was still positive. Hard to explain that away (from its point of view) as the effect of a change in load. It may not have applied that logic, but maybe it should have?

I notice the battery voltage falls to 0V and returns to 28V. I wonder if that was caused by the contactor trying to disconnect the battery? I hope the board controlling the contactor doesn't need a functioning battery to provide power to control the contactor?
My expectation is that both the primary contactor and the backup contractor open when unpowered, and energy to close the contacts comes from either the BCU or the battery itself, under the direction of the BMU. But if the BMU circuits got fried quickly, they might not have been able to enforce their intention to open the contactor. This happened some time (a few seconds) after the initial observed event and we really don't know when the first damage was done to the BCU. Or the battery voltage dropped below the hold voltage of the contractor or the decision threshold of the BMU, causing it to open, the battery voltage could then have rebounded enough to close it again.
Not enough information.
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Old 9th Mar 2013, 01:09
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At a guess, 98 per cent of the discussion here is 100% forensic debrief.

Were I Boeing, that is where I would like the discussion to be.

Likewise Yuasa.

The manufacture of the Yuasa Batteries requires meticulous handwork, scrupulously clean surroundings, and exquisitely pure ingredients and materials.

The CT scans of sections of even the JAL exemplar show problematic bunching, packing, and wrinkling of the electrode stack. Given the design, the geography of the enclosure, and its attendant kit, to ignore the probability that failure is merely a shortened service life due environmental impacts is not far fetched.

On the face of it, that is what Boeing determined, hence the AFR (Accelerated Field Replacement).

It's Friday evening. I'm down to the local for a pint. Maybe I'll run into W. Occam, kick this around.....
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Old 9th Mar 2013, 04:46
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I believe on most airliners, if the batteries are shut off (offline) one way or another, the APU shuts down due to the APU ECU being unpowered. I did it by accident on a 320 a year ago. APU's generally have auto shutdown features, at least on the ground, as well. In the air, usually the crew has to shut it down.

I can't verify this for the 787, but since they are all certified under similar standards, I would guess it would be the same. Engine Fadec's a lot of time have their own Fadec generators that power themselves under normal circumstances, and use ships power if those generator's fail.

I haven't been reading much other than the NTSB stuff. Since they are replacing the whole "battery system", I would guess that they really don't know what the causal factor(s) was. If they had found the cause, they would just fix the singular problem.
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Old 9th Mar 2013, 12:45
  #898 (permalink)  
 
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Me #881,
"If the APU and/or its 2 gennies (starter/generators) fail, perhaps catastrophically, there must remain a power supply to control the APU shutdown, and trigger the fire bottle(s) if necessary. The APU may have a FADEC generating its own power during normal running, but the APU also needs some kind of battery back-up, IMO. (Must admit I'm "winging" this one!)"

inetdog #887,
"...Which also makes it interesting to see that the battery failure "triggered an APU shutdown". Possibly once the fuel was cut off, the fully functional APU managed to generate enough power while coasting down to complete any required sequence. There was no other power source on the plane at the time, but it does sound like the shutdown would have occurred regardless of what other power was available."

Good point. However, isn't it a sort of chicken-and-egg situation? Normally, the APU genny trips off line almost immediately. And, as USMCProbe now says:
"I believe on most airliners, if the batteries are shut off (offline) one way or another, the APU shuts down due to the APU ECU being unpowered."

So, what protects an APU if it catches fire during an auto-shutdown, with no personnel present? (Must emphasise this is not a 787-specific question.)

Last edited by Chris Scott; 9th Mar 2013 at 12:51. Reason: Penultimate para expanded.
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Old 9th Mar 2013, 13:13
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So, what protects the APU if it catched fire during an auto-shutdown, with no personnel present? (Must emphasise this is not a 787-specific question.)
Usually the APUC stays powered for approx 2 mins after the APU shuts down. I think the 737-3/5/500 had problems with this early on as pilots/engs were shutting the battery off as soon as the APU started to shutdown. The consequence was that on the next APU start a failure would occur as the APUC was still in shutdown mode.


Back to the 787.
If Boeing insist on a battery that 'may' fail but it's 'safe' as it will be contained then the APU needs a seperate power source. IE A PMG that will continue to power the APUC/FADEC when the APU is up and running.

If the backup can't be relied upon then the backup needs a backup.

What a mess!
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Old 9th Mar 2013, 13:39
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If the Battery is integrated into the distribution network, it is not a Back Up Battery. It is a Battery that has an additional function in name only. By definition, this functional demand is outside the intent of the regulation, imo.

This battery has the elements of a reliable back up source. Too much was expected, and demanded. Is it a legacy of antiquated obsession with pounds of weight? It may be down to Fire, or reliability. Choose wisely. This situation was predictable, and was predicted. The failure in implementation is down to lack of test, and lack of in service experience. Or, worse.

The CT scans of sections of even the JAL exemplar show problematic bunching, packing, wrinkling and pinching of the electrode stacks. Given the design, the geography of the enclosure, and its attendant kit, to ignore the probability that failure is merely a shortened service life due environmental impacts and/or excessive demand is a mistake.
If this type, specific storage battery is not suitable, and cannot be made safe, then the outcome of the public hearings might be "game-changing".

The box was a stupid PR move, a non starter.....

Last edited by Lyman; 9th Mar 2013 at 15:06.
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