FAA Grounds 787s
Join Date: Jan 2008
Location: uk
Age: 68
Posts: 29
Likes: 0
Received 0 Likes
on
0 Posts
recharging the battery
Bearing in mind these batteries are only a standby and not used in any routine situation.
The self discharge rate of these batteries is I believe 8% @ 21C and 15% per month at 40C. If we take 15% as a worst case. The maximum allowed charging rate for these cells is 1C ie. 65A, say for safety a max charging current of 30A has been selected by the designers that would require 20 mins per month of charging. Adjust the figures to the actual max charging rate.
I am confident enough time is spent hooked up to ground power to recharge these batteries.
The self discharge rate of these batteries is I believe 8% @ 21C and 15% per month at 40C. If we take 15% as a worst case. The maximum allowed charging rate for these cells is 1C ie. 65A, say for safety a max charging current of 30A has been selected by the designers that would require 20 mins per month of charging. Adjust the figures to the actual max charging rate.
I am confident enough time is spent hooked up to ground power to recharge these batteries.
Last edited by Rory166; 22nd Jan 2013 at 18:41. Reason: added comma after 65A
Started the APU?
Posted from Pprune.org App for Android
Posted from Pprune.org App for Android
Originally Posted by TURIN
Started the APU?
Posted from PPRuNe.org App for Android
Posted from PPRuNe.org App for Android
Posted from Pprune.org App for Android
Hi again, TURIN,
We were discussing how to avoid using the APU battery, I think, to avoid having to recharge it. (Sounds crazy, doesn't it?)
(Any schematics for us yet?)
We were discussing how to avoid using the APU battery, I think, to avoid having to recharge it. (Sounds crazy, doesn't it?)
(Any schematics for us yet?)
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes
on
0 Posts
Chris Scott
Only part of the solution would be not charging enroute. It is off handedly suggested by the rule, since this portion suggests the requirement is for minimum (state of) charge for launch, not inflight....
(8) Any lithium ion battery installation whose function is required for safe operation of the airplane must incorporate a monitoring and warning feature that will provide an indication to the appropriate flight crewmembers whenever the state-of-charge of the batteries has fallen below levels considered acceptable for dispatch of the airplane.
So this is a checklist item for flightcrew pre launch.
Again, it seems counterintuitve that the rule would call for inflight charging (maintenance) in a standby system. It does not imply that enroute charging is not allowed, but it could be read that way. NTSB has said the voltage of the battery did not exceed its limit in the JAL accident.
It is hard to fathom that this was not considered long ago, I am sure it was. I would have lobbied for "no charging during flight", perhaps either side of wheels up by 30 minutes minimum. However, that implies charging enroute would need to be prevented, (defeated). If it was possible, some one would.
Technically, charging a standby system in flight is oxymoronic. If the batteries are on line, in an emergency, and the charger is active, the load is borne by the CHARGING SYSTEM, so why have standby batteries at all?
And begs the question I asked awhile back. If the Battery is on line, (under charge) and the draw is in any way variable, see below, @ edmundronald.
Only part of the solution would be not charging enroute. It is off handedly suggested by the rule, since this portion suggests the requirement is for minimum (state of) charge for launch, not inflight....
(8) Any lithium ion battery installation whose function is required for safe operation of the airplane must incorporate a monitoring and warning feature that will provide an indication to the appropriate flight crewmembers whenever the state-of-charge of the batteries has fallen below levels considered acceptable for dispatch of the airplane.
So this is a checklist item for flightcrew pre launch.
Again, it seems counterintuitve that the rule would call for inflight charging (maintenance) in a standby system. It does not imply that enroute charging is not allowed, but it could be read that way. NTSB has said the voltage of the battery did not exceed its limit in the JAL accident.
It is hard to fathom that this was not considered long ago, I am sure it was. I would have lobbied for "no charging during flight", perhaps either side of wheels up by 30 minutes minimum. However, that implies charging enroute would need to be prevented, (defeated). If it was possible, some one would.
Technically, charging a standby system in flight is oxymoronic. If the batteries are on line, in an emergency, and the charger is active, the load is borne by the CHARGING SYSTEM, so why have standby batteries at all?
And begs the question I asked awhile back. If the Battery is on line, (under charge) and the draw is in any way variable, see below, @ edmundronald.
Last edited by Lyman; 22nd Jan 2013 at 23:31.
Join Date: Apr 2008
Location: Paris
Age: 74
Posts: 275
Likes: 0
Received 0 Likes
on
0 Posts
In some Lithium batteries, excessive discharge is as dangerous as overcharge. They are usually protected by discharge cutoffs.
Last edited by edmundronald; 22nd Jan 2013 at 23:23.
Lyman,
The point of a battery is to provide short-term electrical power when other sources of it are not available?
Turning to the APU again, I think we need to understand the raisons dętre (missions) of both the APU battery and the APU itself. There seems to be an assumption by some posters here that:
(a) the APU is only to be used during in-flight abnormal or emergency procedures; and
(b) it should always be possible to start it without recourse to the APU battery.
Lacking access to the FCOM, I can only speculate, but an APU even one that does not have to supply copious amounts of bleed air - weighs a great deal more than a couple of lead-acid batteries, and occupies more space. It must justify its existence. The notion that it is not to be used in Normal Procedures is therefore unlikely. That would also assume that all the airports on your B787 network have rapid-deployment ground-conditioning units and high-rated ground power at every gate or stand at which you will ever have to park. (Preferably, the tugs would supply similar electrics, to enable engine start during push-back.) And that is to ignore your diversion airfields.
Think of an airline like Ethiopian. Does Addis Ababa have such facilities? And what about the other African cities on their network; such as Cairo, Dakar, Johannesburg, Lagos, etc., that they may be planning to send their B787s to later?
Even at the most sophisticated airports, there will be occasions when the crew arrives at the aircraft only to find no suitable ground power available. Thats what an APU is for, and the only way to get it started will be with its dedicated battery. 40 or 50 mins later, you may be getting airborne, with an ETOPS leg later in the flight. Ceasing recharging the battery before take-off could leave you with an insufficiently-charged battery, but we have no data on that.
Depending on the certificated ETOPS assumptions for the aircraft, as I wrote in an earlier post, banning in-flight charging might necessitate starting the APU in flight prior to the ETOPS leg (using generated electrics). If that was unsuccessful, however, you might have to divert. So an interim solution could be to start it before departure, and leave it running until the end of the ETOPS leg. Fortunately, an idle APU uses modest amounts of fuel at high altitude.
The banning of recharging the APU battery inflight would not be tolerable in the long term. The advantage of a dedicated APU battery, such as Boeing traditionally provides, is that it can be used to start the APU even in the event of total generation failure. Aircraft using the main battery for APU start normally cannot risk that.
The point of a battery is to provide short-term electrical power when other sources of it are not available?
Turning to the APU again, I think we need to understand the raisons dętre (missions) of both the APU battery and the APU itself. There seems to be an assumption by some posters here that:
(a) the APU is only to be used during in-flight abnormal or emergency procedures; and
(b) it should always be possible to start it without recourse to the APU battery.
Lacking access to the FCOM, I can only speculate, but an APU even one that does not have to supply copious amounts of bleed air - weighs a great deal more than a couple of lead-acid batteries, and occupies more space. It must justify its existence. The notion that it is not to be used in Normal Procedures is therefore unlikely. That would also assume that all the airports on your B787 network have rapid-deployment ground-conditioning units and high-rated ground power at every gate or stand at which you will ever have to park. (Preferably, the tugs would supply similar electrics, to enable engine start during push-back.) And that is to ignore your diversion airfields.
Think of an airline like Ethiopian. Does Addis Ababa have such facilities? And what about the other African cities on their network; such as Cairo, Dakar, Johannesburg, Lagos, etc., that they may be planning to send their B787s to later?
Even at the most sophisticated airports, there will be occasions when the crew arrives at the aircraft only to find no suitable ground power available. Thats what an APU is for, and the only way to get it started will be with its dedicated battery. 40 or 50 mins later, you may be getting airborne, with an ETOPS leg later in the flight. Ceasing recharging the battery before take-off could leave you with an insufficiently-charged battery, but we have no data on that.
Depending on the certificated ETOPS assumptions for the aircraft, as I wrote in an earlier post, banning in-flight charging might necessitate starting the APU in flight prior to the ETOPS leg (using generated electrics). If that was unsuccessful, however, you might have to divert. So an interim solution could be to start it before departure, and leave it running until the end of the ETOPS leg. Fortunately, an idle APU uses modest amounts of fuel at high altitude.
The banning of recharging the APU battery inflight would not be tolerable in the long term. The advantage of a dedicated APU battery, such as Boeing traditionally provides, is that it can be used to start the APU even in the event of total generation failure. Aircraft using the main battery for APU start normally cannot risk that.
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes
on
0 Posts
Hi Chris.
No, I do understand the role of the APU. Simplified: The APU must be available in an emergency, or other. The APU may need to acquire a start from the APU BATT. Fine. Let's say the APU starter circuit is not available, the APU BATTERY is used to spin up a start.
1. The APU starts, and provides power. Standby Batteries go off line.
2. Once started, the APU has two 225kva generators, capable of powering the aircraft without the need for additional power from APU BATT EMER.
3. The APU won't start in:
a. Normal flight? no problem, the Two main engines have ample power
b. Emergency? Now this is a problem, and the APU cannot supply power, it has not started. so,
c. The APU BATT can supply power to exhaustion, (What is that Requirement?)
d. The RAT deploys, providing ELEC. And HYDRAULIC.
I think my question would be: If using APU for ground power, the APU battery must be recharged in isolation, first, just as one would not attempt a start on APU with APU circuits open, the draw on its start BATTERY could be a serious problem....From the data of these two incidents, the problem seems to be around the BATTERY being on line when using the APU on the ground, and recharging the APUBATT at the same time.
So the answer in the interim may be to start the APU off the GEs before shutdown. And whilst airborne. GE starting Pratt Whitney, that's kind of....cute.....Keep the APU BATT as a STAND BY, unless in an emergency. It seems kind of, creepy, to see the APU started by a cleaning crew., using sensitive LITHION power.
As in JAL/BOS?
No, I do understand the role of the APU. Simplified: The APU must be available in an emergency, or other. The APU may need to acquire a start from the APU BATT. Fine. Let's say the APU starter circuit is not available, the APU BATTERY is used to spin up a start.
1. The APU starts, and provides power. Standby Batteries go off line.
2. Once started, the APU has two 225kva generators, capable of powering the aircraft without the need for additional power from APU BATT EMER.
3. The APU won't start in:
a. Normal flight? no problem, the Two main engines have ample power
b. Emergency? Now this is a problem, and the APU cannot supply power, it has not started. so,
c. The APU BATT can supply power to exhaustion, (What is that Requirement?)
d. The RAT deploys, providing ELEC. And HYDRAULIC.
I think my question would be: If using APU for ground power, the APU battery must be recharged in isolation, first, just as one would not attempt a start on APU with APU circuits open, the draw on its start BATTERY could be a serious problem....From the data of these two incidents, the problem seems to be around the BATTERY being on line when using the APU on the ground, and recharging the APUBATT at the same time.
So the answer in the interim may be to start the APU off the GEs before shutdown. And whilst airborne. GE starting Pratt Whitney, that's kind of....cute.....Keep the APU BATT as a STAND BY, unless in an emergency. It seems kind of, creepy, to see the APU started by a cleaning crew., using sensitive LITHION power.
As in JAL/BOS?
Last edited by Lyman; 22nd Jan 2013 at 23:59.
Join Date: May 2009
Location: sfo
Age: 70
Posts: 309
Likes: 0
Received 0 Likes
on
0 Posts
Lyman, Chris
In the BOS case, it is SOP to use APU power only for normal turns. There is a limitation on the APU that once it is shut down, it requires 25 minutes cooldown due to shaft bowing before it can be restarted. So, on a 90 minute turn, they start it on taxi-in to the gate, and leave it running for the entire turn. They don't even bother with GPU power unless the aircraft is going to be on the ground for a longer time.
Join Date: Oct 2007
Location: brasil
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
The point of a battery is to provide short-term
electrical power when other sources of it are not available?
I am sure you checked on Boeings´homepage their remarks about the
move from a hydraulic to an electrical brake system.
So may be one source of the multiple independant power distributions
to the brakes could be the battery itself.--For normal operation!
Lots of talk about charging, discharging being the problem, fact is I had a Li battery, fresh from the manufacturer go bang while in storage. Not a big battery, but still. The manufacturer could not explain why.
Per
Per
Last edited by Ancient Mariner; 23rd Jan 2013 at 06:14.
Lots of questions here.
Here goes.
1. No way am I posting "EXPORT CONTROLLED-BOEING PROPRIETARY-Copyright unpublished work. IE SCHEMATICS.
Sorry but I have a mortgage and mouths to feed.
I will however enter into discussion to try to increase knowledge and understanding, especially mine.
2. Referring to my own hand written notes, the battery can be recharged on the a/c in less than 90 mins.
3. The APU can be started using power from either: APU Hot Battery Bus, AC Bus L1 or AC Bus R2. Depending on which busses are powered, which in turn will depend on what power sources you have available. EG Engine Gen, Ext Pwr (Two Fwd One Aft).
4. Brakes systems are powered from Hot Battery Bus when no normal AC Bus is available. IE. Towing without APU. In an emergency though, only three of four, brake systems are powered- from the Backup Bus, which of course, can receive power from the RAT Gen.
Posted from Pprune.org App for Android
Here goes.
1. No way am I posting "EXPORT CONTROLLED-BOEING PROPRIETARY-Copyright unpublished work. IE SCHEMATICS.
Sorry but I have a mortgage and mouths to feed.
I will however enter into discussion to try to increase knowledge and understanding, especially mine.
2. Referring to my own hand written notes, the battery can be recharged on the a/c in less than 90 mins.
3. The APU can be started using power from either: APU Hot Battery Bus, AC Bus L1 or AC Bus R2. Depending on which busses are powered, which in turn will depend on what power sources you have available. EG Engine Gen, Ext Pwr (Two Fwd One Aft).
4. Brakes systems are powered from Hot Battery Bus when no normal AC Bus is available. IE. Towing without APU. In an emergency though, only three of four, brake systems are powered- from the Backup Bus, which of course, can receive power from the RAT Gen.
Posted from Pprune.org App for Android
Lyman.
Cleaners do not operate cockpit systems. Unless they have been trained and authorised.
Posted from Pprune.org App for Android
Cleaners do not operate cockpit systems. Unless they have been trained and authorised.
Posted from Pprune.org App for Android
Lyman.
The APU Battery supplies the APU Hot Battery Bus ONLY. AFAIK it's job is to start the APU when no other power is available and power the Nav Lights when towing without APU. Thats it.
Posted from Pprune.org App for Android
The APU Battery supplies the APU Hot Battery Bus ONLY. AFAIK it's job is to start the APU when no other power is available and power the Nav Lights when towing without APU. Thats it.
Posted from Pprune.org App for Android
Join Date: Jul 2007
Location: Germany
Posts: 556
Likes: 0
Received 0 Likes
on
0 Posts
Ancient Mariner,
Of course that can happen if there is a defect (either from manufacturing, as in your case, or from prolonged use, e. g. through formation of dendrites), but it is much rarer than during charge/discharge, and having it happen on a relatively small fleet of aircraft twice within a few days is stretching credibility a bit too far.
So, yes, problems with charge/discharge control seems the best bet right now.
I smell software.
It is very hard to demonstrate software to have an "extremely remote" failure probability, so I read the special conditions for the Li-Ion exemption as requiring an additional (fail-safe) over-temperature and over-voltage cutoff, in case the (software-controlled) battery control system fails.
Bernd
Lots of talk about charging, discharging being the problem, fact is I had a Li battery, fresh from the manufacturer go bang while in storage. Not a big battery, but still. The manufacturer could not explain why.
So, yes, problems with charge/discharge control seems the best bet right now.
I smell software.
It is very hard to demonstrate software to have an "extremely remote" failure probability, so I read the special conditions for the Li-Ion exemption as requiring an additional (fail-safe) over-temperature and over-voltage cutoff, in case the (software-controlled) battery control system fails.
Bernd
Join Date: Oct 2007
Location: brasil
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
TURIN
Thank you very much Turin!
From your hand notes..., is the MAIN BATTERY for normal operation in flight
only a backup/emergency source, or is it also used as normal power distribution?
--Does it need to be charged in flight?
Braking system: Is there any hydraulic backup (accumulator), or is everything electric? --Battery= backup?
From your hand notes..., is the MAIN BATTERY for normal operation in flight
only a backup/emergency source, or is it also used as normal power distribution?
--Does it need to be charged in flight?
Braking system: Is there any hydraulic backup (accumulator), or is everything electric? --Battery= backup?
From what I can see the only system that is supplied directly from the Hot Battery Bus in normal flight, is the Wireless control units for the emergency lights.
Does it need to be kept fully charged in flight?
I would say yes. If you are in such dire straights that any systems need power from your main battery, you need every amp for as long as possible.
Brakes are ALL electric. No hydraulic back up. Just multiple independent power sources.
Posted from Pprune.org App for Android
Does it need to be kept fully charged in flight?
I would say yes. If you are in such dire straights that any systems need power from your main battery, you need every amp for as long as possible.
Brakes are ALL electric. No hydraulic back up. Just multiple independent power sources.
Posted from Pprune.org App for Android
Join Date: Aug 2007
Location: London, New York, Paris, Moscow.
Posts: 3,632
Likes: 0
Received 0 Likes
on
0 Posts
I think you have to take a step away from the "normal" with this cab, and think what the advantages of all electric are.
My first has to be the electric compressors. Even with a double flame out surely there must exist the provision to, even partially, retain pressurisation to sustain the passengers? Well so long as you can get the apu running and both apu gen's online.....
Any thoughts?
My first has to be the electric compressors. Even with a double flame out surely there must exist the provision to, even partially, retain pressurisation to sustain the passengers? Well so long as you can get the apu running and both apu gen's online.....
Any thoughts?