FAA Grounds 787s
RR
I think we are both on the same page now.
Just one thing.
The towing switch is a selected function, not automatic.
Depending on Main Batt charge state, there may only be enough power for a half hour tow.
Likewise, refuelling on batt, there is only enough power for approx 15 mins. The logic being that 15 mins is enough time to get enough fuel in to the left main fuel tank to start the APU.
Just to be clear, the BDM sits beteen the battery and the hot batt bus. The hot bat bus is isolated from the main DC bus unless DC bus power is lost. 
I think we are both on the same page now.
Just one thing.
The towing switch is a selected function, not automatic.
Depending on Main Batt charge state, there may only be enough power for a half hour tow.
Likewise, refuelling on batt, there is only enough power for approx 15 mins. The logic being that 15 mins is enough time to get enough fuel in to the left main fuel tank to start the APU.
Quote:
The Main Bat again will only be supplying if main DC is not supplying.
I.e. when there is no DC (lower than a given value) in the BUS. I.e. when nothing (from AC source) is feeding DC bus. In this condition MAIN battery supplies (automatically) required energy to the bus through the BDM. (if batt. switch is ON)
The Main Bat again will only be supplying if main DC is not supplying.
I.e. when there is no DC (lower than a given value) in the BUS. I.e. when nothing (from AC source) is feeding DC bus. In this condition MAIN battery supplies (automatically) required energy to the bus through the BDM. (if batt. switch is ON)
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@RR-NDB I think we,re all happy with the notion that the main problem is centred around the care of thr battery. As you say, the voltage-range on a laptop "full" to "empty" is only 1V. This has to be taken in context. the discharge characteristics of the cell are such that there is minimal voltage-change over a large portion of the charge/discharge curves. A bit like the "reserve"fuel that every commercial aircraft tankers around on every flight....it only gets used in the rare case like the GIMLI Glider I don't know the statistics but would hazard a guess of once in 5 years worldwide.
Despite the forgoing, the SAFE USABLE amount of power is still ahead on the weight/volume stakes.
Yet here we have 50 aircraft which have, statistically, EACH used up their "reserve electricity" supply 3 TIMES in their service-life.
That doesn't even factor-in the age-spread across deliveries, so the mean aircraft service- life is probably ~2 years....That makes the apparent cover-up even more dramatic.
Were each individual sub-cell to be spaced above and below with a thermal insulator and connected to it's "common" (Paralleling) busbars with fusible-links, this, IMO would go some way towards addressing the present inherent problems.
Any faulty/abused sub-cell would tend to self-isolate and burn itself out without compromising the entire cell and battery-pack. Yes, i appreciate it would reduce the capacity of the individual cell-assembly,but the whole battery could still be available.
Regarding the modellers....there are a LOT more out there than the number of "screamliner2 batteries in service....by the nature of things, their usage is much more erratic, timewise, their charge-discharge cycles are heavy, intense and frequent. there are THOUSANDS of sucessful flights performed worldwide every week...so the "Crash'n burn scenario is statistically miniscule....and these are not "Certified by the CAA" but commercial, cheap as chips, mainstream items bought and operated by untrained/self-taught amateurs..
I'd suggest anyone interested ,should look at the "RUNRYDER" model Heli forum. a perusal of the electric Fora could prove enlightening.
Despite the forgoing, the SAFE USABLE amount of power is still ahead on the weight/volume stakes.
Yet here we have 50 aircraft which have, statistically, EACH used up their "reserve electricity" supply 3 TIMES in their service-life.
That doesn't even factor-in the age-spread across deliveries, so the mean aircraft service- life is probably ~2 years....That makes the apparent cover-up even more dramatic.
Were each individual sub-cell to be spaced above and below with a thermal insulator and connected to it's "common" (Paralleling) busbars with fusible-links, this, IMO would go some way towards addressing the present inherent problems.
Any faulty/abused sub-cell would tend to self-isolate and burn itself out without compromising the entire cell and battery-pack. Yes, i appreciate it would reduce the capacity of the individual cell-assembly,but the whole battery could still be available.
Regarding the modellers....there are a LOT more out there than the number of "screamliner2 batteries in service....by the nature of things, their usage is much more erratic, timewise, their charge-discharge cycles are heavy, intense and frequent. there are THOUSANDS of sucessful flights performed worldwide every week...so the "Crash'n burn scenario is statistically miniscule....and these are not "Certified by the CAA" but commercial, cheap as chips, mainstream items bought and operated by untrained/self-taught amateurs..
I'd suggest anyone interested ,should look at the "RUNRYDER" model Heli forum. a perusal of the electric Fora could prove enlightening.
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On previous posts (57min and 12 min)
Hi,
TURIN,
As i understand to make impossible battery receive energy from the DC BUS (where voltage is not "regulated" i.e. may vary in a range as any DC BUS)
I imagine the BDM function as:
If MAIN batt. is switched ON., (normally should be ON because itīs supposed to be "healthy") and DC BUS power is lost BDM "connects" AUTOMATICALLY MAIN batt. to maintain DC BUS with nominal voltage. The automatic (fast in miliseconds range) transfer is ABSOLUTELY NECESSARY. Why? In previous a/c the DC BUS is ALWAYS connected to the battery. Not in 787. The immediate connection is done by the "valve" (BDM) you mentioned.
As it should be. Not a critical item. Important but not critical. Manual is OK.
You mean,APU batt. OK? (Not MAIN batt. state)
Itīs adequate.
cockney steve: Ref 08:12
Certainly.
Will comment later on other points.
Rgds,
TURIN,
Just to be clear, the BDM sits beteen the battery and the hot batt bus.
As i understand to make impossible battery receive energy from the DC BUS (where voltage is not "regulated" i.e. may vary in a range as any DC BUS)
The hot bat bus is isolated from the main DC bus unless DC bus power is lost.
If MAIN batt. is switched ON., (normally should be ON because itīs supposed to be "healthy") and DC BUS power is lost BDM "connects" AUTOMATICALLY MAIN batt. to maintain DC BUS with nominal voltage. The automatic (fast in miliseconds range) transfer is ABSOLUTELY NECESSARY. Why? In previous a/c the DC BUS is ALWAYS connected to the battery. Not in 787. The immediate connection is done by the "valve" (BDM) you mentioned.
The towing switch is a selected function, not automatic.
As it should be. Not a critical item. Important but not critical. Manual is OK.
Depending on Main Batt charge state, there may only be enough power for a half hour tow.
Likewise, refuelling on batt, there is only enough power for approx 15 mins. The logic being that 15 mins is enough time to get enough fuel in to the left main fuel tank to start the APU.
cockney steve: Ref 08:12
I think we,re all happy with the notion that the main problem is centred around the care of thr battery.
Will comment later on other points.
Rgds,
Last edited by RR_NDB; 14th Feb 2013 at 11:03.
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Likewise, refuelling on batt, there is only enough power for approx 15 mins. The logic being that 15 mins is enough time to get enough fuel in to the left main fuel tank to start the APU.
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SW "protection"?
Hi,
green granite:
May be a limitation in order to leave energy on battery for other uses.
And the 65 Ah (260 A for 15 minutes) would not happen (remember the Peukert effect)
green granite:
May be a limitation in order to leave energy on battery for other uses.
And the 65 Ah (260 A for 15 minutes) would not happen (remember the Peukert effect)
Are you really saying that the basic circuitry needed to refuel one tank draws 260 Amps?
An example: Many years ago we had a flat battery on a 737-200. It was so flat that there was insufficient power available to operate the external AC power contactor. Fortunately the 737 also had a DC external power connector in the EE bay.
787 does not have that option.
I don't have the schematics with me and I can't remember whether the refuelling battery switch is connected to the Main hot bat bus or the APU hot bat bus.
I imagine the BDM function as:
If MAIN batt. is switched ON., (normally should be ON because itīs supposed to be "healthy") and DC BUS power is lost BDM "connects" AUTOMATICALLY MAIN batt. to maintain DC BUS with nominal voltage. The automatic (fast in miliseconds range) transfer is ABSOLUTELY NECESSARY. Why? In previous a/c the DC BUS is ALWAYS connected to the battery. Not in 787. The immediate connection is done by the "valve" (BDM) you mentioned.
If MAIN batt. is switched ON., (normally should be ON because itīs supposed to be "healthy") and DC BUS power is lost BDM "connects" AUTOMATICALLY MAIN batt. to maintain DC BUS with nominal voltage. The automatic (fast in miliseconds range) transfer is ABSOLUTELY NECESSARY. Why? In previous a/c the DC BUS is ALWAYS connected to the battery. Not in 787. The immediate connection is done by the "valve" (BDM) you mentioned.
The BDM is between the battery and the HOT BAT BUS not the main DC Busses. As it's name suggests the Hot Bat Bus is always 'live'.
The Hot Bat Bus is connected to the Main DC Busses via the Hot Bat Bus Contactor.
Quote:
Depending on Main Batt charge state, there may only be enough power for a half hour tow.
You mean,APU batt. OK? (Not MAIN batt. state)
Depending on Main Batt charge state, there may only be enough power for a half hour tow.
You mean,APU batt. OK? (Not MAIN batt. state)
The Main Bat powers the essential towing items such as VHF1, brakes (& Anti collision beacons-I think).
There is a very simple indicator on the flight deck that shows battery state when the a/c is unpowered. It simply shows High, Medium, Low.
When beginning a tow, this will give the engineer/mechanic a reference to how long they have to complete the tow. I have also heard that automatic load shedding will occur if the bat state gets too low, IE. VHF1 is lost. etc.
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Since the discharge curve for lead-acid and Li-Ion batteries are very different Peukert's law would be much nearer to being negligible for Li-Ion, and if the batteries are allowed to rise in temperature to 131°F you get nearly as much energy no matter how hard you drive them.
Last edited by green granite; 14th Feb 2013 at 12:52.
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TURIN Thanks for your wealth of knowledge and your no nonsense style.
It seems that there are some minimal demands on these Batteries when the a/c is powered down, eg, POS lights, FUEL indicator, DOOR position, etc.
A question I asked long long ago. These Lithium Ion batteries have a well proven long life as to SOC, and a less proven profile relative to daily use, discharge, environmental factors, and Handling error.
Would it have been perhaps a better idea to have a powered down 'Battery system' of a more proven nature to accomplish the mundane chores we are discussing here?
The Backup Batteries are a flight critical system, and perform just fine in that regard, it would seem.....?
Penny wise, pound foolish?
It seems that there are some minimal demands on these Batteries when the a/c is powered down, eg, POS lights, FUEL indicator, DOOR position, etc.
A question I asked long long ago. These Lithium Ion batteries have a well proven long life as to SOC, and a less proven profile relative to daily use, discharge, environmental factors, and Handling error.
Would it have been perhaps a better idea to have a powered down 'Battery system' of a more proven nature to accomplish the mundane chores we are discussing here?
The Backup Batteries are a flight critical system, and perform just fine in that regard, it would seem.....?
Penny wise, pound foolish?
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787 batteries "scheme"
Hi,
TURIN:
Redundancy (DC EXT PWR) was necessary.
So, 787 has:
1) Relay/contactor inside battery (as we imagine from pictures) for batt. ON/OFF
2) BDM between STD batt. connector and HOT BATT BUS
3) HOT BATT BUS contactors to DC BUSsess (LH and RH)
Electrically speaking is similar what first thought.
Indeed, brakes, comm and Anti collision beacons, certainly.
I initially thought of APU batt. for this items but to save weight and cost you donīt have higher current cabling between batteries. Just control wiring.
I consider it enough! The Li ion actually doesnīt require a voltage indicator. itīs voltage span is small. 3 levels is perfect. Simple and efficient.The load shedding is a good approach to allow a prioritized graceful degradation. Avoiding damage to any cell. (other batteries are more tolerant)
The design sounds perfect.
green granite:
One of the appeals for designers adopt it.
For a 65A (75 A nominal) What would be a designers (787) peak limit?
(For MAIN batt. i mean) This specific aspect concerns me.
For APU i guess there is no big problem. Soft start, etc.
My concern in the MAIN also is: Li ion use was really very important?
WHY?
TURIN:
Redundancy (DC EXT PWR) was necessary.
The Hot Bat Bus is connected to the Main DC Busses via the Hot Bat Bus Contactor.
1) Relay/contactor inside battery (as we imagine from pictures) for batt. ON/OFF
2) BDM between STD batt. connector and HOT BATT BUS
3) HOT BATT BUS contactors to DC BUSsess (LH and RH)
Electrically speaking is similar what first thought.
The APU Bat when towing only powers the Position (Nav) lights.The Main Bat powers the essential towing items such as VHF1, brakes (& Anti collision beacons-I think).
I initially thought of APU batt. for this items but to save weight and cost you donīt have higher current cabling between batteries. Just control wiring.
There is a very simple indicator on the flight deck that shows battery state when the a/c is unpowered. It simply shows High, Medium, Low. When beginning a tow, this will give the engineer/mechanic a reference to how long they have to complete the tow. I have also heard that automatic load shedding will occur if the bat state gets too low, IE. VHF1 is lost. etc.
The design sounds perfect.
green granite:
Since the discharge curve for lead-acid and Li-Ion batteries are very different Peukert's law would be much nearer to being negligible for Li-Ion, and if the batteries are allowed to rise in temperature to 131°F you get nearly as much energy no matter how hard you drive them.
One of the appeals for designers adopt it.
no matter how hard you drive them.
For a 65A (75 A nominal) What would be a designers (787) peak limit?(For MAIN batt. i mean) This specific aspect concerns me.
For APU i guess there is no big problem. Soft start, etc.
My concern in the MAIN also is: Li ion use was really very important?
WHY?
Last edited by RR_NDB; 14th Feb 2013 at 14:47. Reason: Add quotes
Working backward, FAA accepted a single cell would not cause propagation (further runaway). So the assumption is BOEING designed, built, and tested a platform that demonstrated this to the satisfaction of BOEING. And to FAA.
So working backwards, Boeing did not test it for certification, unless they deliberately introduced a battery with known design flaws and covered it up.
2) The problem to isolate a defective cell is: You need a costly relay and you reduce the voltage of the battery. Itīs not practical.
Last edited by peter we; 14th Feb 2013 at 20:30.
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The individual cells are monitored and isolated if defective, they have to be. A relay costs a few dollars in a $16k battery FFS
Ultimately, where is the power for the relays coming from? A back-up Ni-Cad??
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To say nothing of the huge current they would have to be capable of switching, I think you would need an OCB to do that job.
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The individual cells are monitored and isolated if defective, they have to be.
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Precisely. It's all or nothing, and the Battery better disconnect at the front of the case, from both leads. God forbid an external short from a terminal to the steel case. That could then end up as a dead short for the entire system.
That is what the "Zero Voltage" on ANA was all about. Any shutdown must be an instant complete removal from the circuit. And the reason I think the system worked for ANA.
That is what the "Zero Voltage" on ANA was all about. Any shutdown must be an instant complete removal from the circuit. And the reason I think the system worked for ANA.
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posts 820-824.
individual relays on the 8 cells would not work The real problem in thermal -runaway, is that each "cell" is, in fact a BATTERY
Another member has already pointed this out on one of the numerous therads running.
A "cell" consists of several small cells in PARALLELL this is the only way to achieve the design objectives of discharge-rate/overall capacity/fault-limitation.
I have already suggested, the way forward is to link each of these sub-cells to the "Cell" terminal with a fusible link. If you look at the photos, you will see the terminal post is rivited onto the top of the cell-casing....I'd suggest that Pos. and Neg, busbars go down the stack and the individual sub-cells are parallelled to them. so, fusible links-each cell to busbar....fusible link of the necessarily higher order , to connect the internal busbar to it's terminal.
Cheap, effective AND EVERY SINGLE CELL HAS PROTECTION FROM OVERHEAT
Irrespective of wether it's caused by cell-fault, overcurrent, overcharge or over-discharge.
Assuming Boeing refuse to lose face and ditch the technology altogether, this would majorly address the safety-issue....the charger-unit and the connection direct to a "dirty" bus (OK, via a contactor/relay) are something else.
A failsafe strategy as outlined above would be cheap and easy to integrate and be very cost-effective.
Boeing/Thales can have the benefit of my "expertise" for free!!!!
No warranty given or implied. (like the existing batteries, then ?)
individual relays on the 8 cells would not work The real problem in thermal -runaway, is that each "cell" is, in fact a BATTERY
Another member has already pointed this out on one of the numerous therads running.
A "cell" consists of several small cells in PARALLELL this is the only way to achieve the design objectives of discharge-rate/overall capacity/fault-limitation.
I have already suggested, the way forward is to link each of these sub-cells to the "Cell" terminal with a fusible link. If you look at the photos, you will see the terminal post is rivited onto the top of the cell-casing....I'd suggest that Pos. and Neg, busbars go down the stack and the individual sub-cells are parallelled to them. so, fusible links-each cell to busbar....fusible link of the necessarily higher order , to connect the internal busbar to it's terminal.
Cheap, effective AND EVERY SINGLE CELL HAS PROTECTION FROM OVERHEAT
Irrespective of wether it's caused by cell-fault, overcurrent, overcharge or over-discharge.
Assuming Boeing refuse to lose face and ditch the technology altogether, this would majorly address the safety-issue....the charger-unit and the connection direct to a "dirty" bus (OK, via a contactor/relay) are something else.
A failsafe strategy as outlined above would be cheap and easy to integrate and be very cost-effective.
Boeing/Thales can have the benefit of my "expertise" for free!!!!
No warranty given or implied. (like the existing batteries, then ?)
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The "APU" Battery, and the "MAIN" Battery. These are misnomers.
Each Battery system is a group of eight separate batteries. Each battery has three cells.
The Eight Batteries are connected in series and contained in a Stainless Steel enclosure.
It is not possible to "isolate" one battery from its seven sisters. To do so interrupts the series.
One bad battery, no more "group". IF the system works correctly.
I hope I have that right, I have been referring to the Back up power system that way since the outset.
For whatever reason the nomenclature took that turn, it misleads. "Ah, just the one "cell", then, not so bad...." Any problem with one of the eight batteries disables the entire back up system. That is a game changer, appearance-wise.
The ANA Captain reported a "zero Voltage". As if that is an anomaly?
That is not an anomaly, that is the design. And it frames the dependability of the flight critical system as suspect.
Each Battery system is a group of eight separate batteries. Each battery has three cells.
The Eight Batteries are connected in series and contained in a Stainless Steel enclosure.
It is not possible to "isolate" one battery from its seven sisters. To do so interrupts the series.
One bad battery, no more "group". IF the system works correctly.
I hope I have that right, I have been referring to the Back up power system that way since the outset.
For whatever reason the nomenclature took that turn, it misleads. "Ah, just the one "cell", then, not so bad...." Any problem with one of the eight batteries disables the entire back up system. That is a game changer, appearance-wise.
The ANA Captain reported a "zero Voltage". As if that is an anomaly?
That is not an anomaly, that is the design. And it frames the dependability of the flight critical system as suspect.
Last edited by Lyman; 15th Feb 2013 at 12:29.
Airbus dumping Lithium batteries on A350
http://www.nytimes.com/aponline/2013...ries.html?_r=0
a clever move by Airbus at just the right time ! This will make it pretty well impossible for Boeing to now claim they can come up with an adequate method to continue with Lithium, where the other mainstream manufacturer also now says they can't be relied on. It will derail the 787 programme for months. Meanwhile the A350 test programme will start with the Lithiums, but without being certified for pax of course.
It is, of course, the right course of action. I wonder if Boeing have even started the drawings for going back to previous battery technology.
http://www.nytimes.com/aponline/2013...ries.html?_r=0
a clever move by Airbus at just the right time ! This will make it pretty well impossible for Boeing to now claim they can come up with an adequate method to continue with Lithium, where the other mainstream manufacturer also now says they can't be relied on. It will derail the 787 programme for months. Meanwhile the A350 test programme will start with the Lithiums, but without being certified for pax of course.
It is, of course, the right course of action. I wonder if Boeing have even started the drawings for going back to previous battery technology.