787 Batteries and Chargers - Part 1
saptzae:
It was just intended to be a block diagram to show the major components and
their interaction. I can redraw to show all the wires, but there wasn't
enough space between the cells on the original sketch.
From what we know already, the 787 battery does have separate circuits
for measurement & balancing. Though i'm not advocating it, it is possible
combine both functions by time sharing a single wire. ie: Charge / balance for a
period, then disconnect and measure for a period. Many modern lead acid
chargers work in exactly that way.
We have to agree to differ on the temp sensing . A single cell's temp
gradient would be easier to detect if the sensor were at the cell, rather
than several inches away at the other side of the case. As the temp sensor
is part of an overall feedback loop controlling charge current, the closer
to the cell being monitored, the less phase lag there is in the loop, thus
providing a faster overall response. Ideally, it would be embedded in the
internal folds of the cells during production, but that may be asking too
much.
As for the transient detection, that could be done by sensing cell voltage
dv/dt, either using a fast a/d converter, or much simpler, an analog
differentiator feeding a limit comparator, which then generates an interrupt
to the bms processor. I know it might be more elegant to use an a/d, but it's
not a no cost option as you not only need the fast a/d, but all the software
to drive it as well. Not difficult overall, but who knows what's on those bms
boards already.
If the temp sensor is built into the cell, then why not a pressure sensor as
well ?, though it would increase the cost considerably. Still, for a new
application such as this, perhaps extreme belt and braces will be the only
way to satisfy the regulators until more in service experience is gained...
It was just intended to be a block diagram to show the major components and
their interaction. I can redraw to show all the wires, but there wasn't
enough space between the cells on the original sketch.
From what we know already, the 787 battery does have separate circuits
for measurement & balancing. Though i'm not advocating it, it is possible
combine both functions by time sharing a single wire. ie: Charge / balance for a
period, then disconnect and measure for a period. Many modern lead acid
chargers work in exactly that way.
We have to agree to differ on the temp sensing . A single cell's temp
gradient would be easier to detect if the sensor were at the cell, rather
than several inches away at the other side of the case. As the temp sensor
is part of an overall feedback loop controlling charge current, the closer
to the cell being monitored, the less phase lag there is in the loop, thus
providing a faster overall response. Ideally, it would be embedded in the
internal folds of the cells during production, but that may be asking too
much.
As for the transient detection, that could be done by sensing cell voltage
dv/dt, either using a fast a/d converter, or much simpler, an analog
differentiator feeding a limit comparator, which then generates an interrupt
to the bms processor. I know it might be more elegant to use an a/d, but it's
not a no cost option as you not only need the fast a/d, but all the software
to drive it as well. Not difficult overall, but who knows what's on those bms
boards already.
If the temp sensor is built into the cell, then why not a pressure sensor as
well ?, though it would increase the cost considerably. Still, for a new
application such as this, perhaps extreme belt and braces will be the only
way to satisfy the regulators until more in service experience is gained...
Last edited by syseng68k; 9th Feb 2013 at 11:50.
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Li Ion batteries are "aviation friendly"?
Hi,
"Fault Tolerance and Graceful Degradation" are essential characteristics of good Systems.
An aircraft to perform this must rely on adequate parts.
I question the use of Li Ion batteries as MAIN and APU with the current "aviation industry conditions". (including Certification)
IMHO we still lack SEVERAL IMPORTANT pre-requisites to use these batteries for above mentioned applications in airliners.
The pre-requisites cover ALL issues capable to generate (BIG) problems ranging from technical to organizational aspects.
If EADS is questioning and considering alternate solutions for A350 i think they are correct.
We engineers like "hi performance" parts in our design.
But, we must question everything prior to mass producing.
"Fault Tolerance and Graceful Degradation" are essential characteristics of good Systems.
An aircraft to perform this must rely on adequate parts.
I question the use of Li Ion batteries as MAIN and APU with the current "aviation industry conditions". (including Certification)
IMHO we still lack SEVERAL IMPORTANT pre-requisites to use these batteries for above mentioned applications in airliners.
The pre-requisites cover ALL issues capable to generate (BIG) problems ranging from technical to organizational aspects.
If EADS is questioning and considering alternate solutions for A350 i think they are correct.
We engineers like "hi performance" parts in our design.
But, we must question everything prior to mass producing.
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Well, the full-size picture (post 581) seems to show some of the wires in the harness being too short and under tension (e.g. one near the upper right corner) - a priori I am not too impressed by the quality of this assembly.
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Temperature Sensing ?
An observation based on the photograph posted above by Speed of Sound:
The central two connecting bus-bars each have two "connections", compared to one for each of the other intermediate bus-bars - one of these "connections" is under the white mass.
I notice that one of the "connections" to each bus-bar appears to have thicker wire (the ones to the centre of the bus-bar). Is it possible that these are two-wire connections to something like a thermocouple?
This might be one form of temperature sensing, but not really enough to give comfort in the high level of monitoring.
The central two connecting bus-bars each have two "connections", compared to one for each of the other intermediate bus-bars - one of these "connections" is under the white mass.
I notice that one of the "connections" to each bus-bar appears to have thicker wire (the ones to the centre of the bus-bar). Is it possible that these are two-wire connections to something like a thermocouple?
This might be one form of temperature sensing, but not really enough to give comfort in the high level of monitoring.
More bang for your buck
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The thing I notice is that the connectors for most of the wires seem to be push on 'spade' type connectors, which I wouldn't have dreamt of using for mission critical set-ups because of their inexplicable tendency to become loose for no apparent reason. (it may be that I'm interpreting the image wrongly)
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GreenGranite,
The connectors all seem to have crosshead screw atttachments. Whether there is a 'spade' or circular connecting lug cannot be seen.
On a more general point right at the beginning of this thread Machaca posted that:
This raises questions first about the accuracy of the algorithm for forecasting the inflection point. But also that the algorithm may rely on inputs of 'all temperature conditions' which may not actually be available in that battery pack.
The connectors all seem to have crosshead screw atttachments. Whether there is a 'spade' or circular connecting lug cannot be seen.
On a more general point right at the beginning of this thread Machaca posted that:
Securaplane has developed a method for accurately detecting the inflection point which has eluded battery experts for years and is critical in reducing an overcharge condition. This patented method of charging ensures that the battery receives the optimum amount of charge for all temperature conditions combined with various battery states of charge.
I notice that one of the "connections" to each bus-bar appears to have thicker wire (the ones to the centre of the bus-bar). Is it possible that these are two-wire connections to something like a thermocouple?
Zip ties. Not used much in my day. We preferred cable lacing: Cable lacing - Wikipedia, the free encyclopedia
Some of those wires appear to be pulled pretty tight as well.
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@syseng68k
Balancing performs discharge only < 0.05C (my estimate). Charging is serial at up to 1C. Multiplexing charger with Li cells would rely on assumptions on peak cell voltage. Extra connections to same terminal will also help with detecting wire breakage.
I like the pressure sensor idea, it would be very sensitive detecting arcing inside a cell. Actually, silicon pressure sensors have temperature sensors built in for calibration against temperature variations
.
@Alison747
There may be a temperature sensor under the white mass. There is no indication of per cell temperature sensors.
@EEngr
Concur, wire terminations are with heat-shrink tube and are tied tight to increase vibration resistance.
@Ian
IMHO circular lugs used.
I pointed the securaplane battery patent out here:
http://www.pprune.org/tech-log/50569...ml#post7645076
It is one of those patents one gets to get a patent for making life harder for the competition to sue one. Well, and a little for marketing hype too. As to its merit, inflection, prediction, assumption is IMHO a demerit.
Guess we will learn more BMU details from the NTSB report.
Balancing performs discharge only < 0.05C (my estimate). Charging is serial at up to 1C. Multiplexing charger with Li cells would rely on assumptions on peak cell voltage. Extra connections to same terminal will also help with detecting wire breakage.
I like the pressure sensor idea, it would be very sensitive detecting arcing inside a cell. Actually, silicon pressure sensors have temperature sensors built in for calibration against temperature variations
. @Alison747
There may be a temperature sensor under the white mass. There is no indication of per cell temperature sensors.
@EEngr
Concur, wire terminations are with heat-shrink tube and are tied tight to increase vibration resistance.
@Ian
IMHO circular lugs used.
I pointed the securaplane battery patent out here:
http://www.pprune.org/tech-log/50569...ml#post7645076
It is one of those patents one gets to get a patent for making life harder for the competition to sue one. Well, and a little for marketing hype too. As to its merit, inflection, prediction, assumption is IMHO a demerit.
Guess we will learn more BMU details from the NTSB report.
Last edited by saptzae; 9th Feb 2013 at 19:47.
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Battery Management System
I note there has been extensive discussion surrounding the apparent lack of temperature sensing for each of the 8 series cells in these battery packs.
I mentioned many posts ago the need in the manufacturing process to match cells for both "impedance" and "temperature". Each is relative to the other, so it is possible to deduce during the charging cycle (probably pulsed DC) the impedance of each cell under charge and by using a "look up table" determine accurately the related cell temperature.
No need for any more wires/sensors.
I mentioned many posts ago the need in the manufacturing process to match cells for both "impedance" and "temperature". Each is relative to the other, so it is possible to deduce during the charging cycle (probably pulsed DC) the impedance of each cell under charge and by using a "look up table" determine accurately the related cell temperature.
No need for any more wires/sensors.
Last edited by mm43; 9th Feb 2013 at 20:18.
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Wish for industry cooperation
There is no need for everyone developing their own square wheel battery.
There already is cooperation in computer and electronics technology to set standards, be it software like Linux, the W3C or Wifi or OpenGL.
I suggest that all air-framers set up a battery group or consortium to further develop the technology for the benefit of all. It would substantially cut cost and improve quality.
There already is cooperation in computer and electronics technology to set standards, be it software like Linux, the W3C or Wifi or OpenGL.
I suggest that all air-framers set up a battery group or consortium to further develop the technology for the benefit of all. It would substantially cut cost and improve quality.
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what is below the white mass?
saptzae,
You wrote:
There may be a temperature sensor under the white mass
Could well be!
Look at the white mass in post#581 and compare the position of this mass with the position of some light grey stuff in the picture of the damaged battery in post#1.
But more important: Look at the picture of an undamaged battery in post#193 in the thread "ANA 787 makes emergency landing due battery fire warning"
You clearly see a white box attached to the thicker wire at a position corresponding to the position of the stuff/mass mentioned above.
brgds
You wrote:
There may be a temperature sensor under the white mass
Could well be!
Look at the white mass in post#581 and compare the position of this mass with the position of some light grey stuff in the picture of the damaged battery in post#1.
But more important: Look at the picture of an undamaged battery in post#193 in the thread "ANA 787 makes emergency landing due battery fire warning"
You clearly see a white box attached to the thicker wire at a position corresponding to the position of the stuff/mass mentioned above.
brgds
Last edited by grebllaw123d; 9th Feb 2013 at 21:13.
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Standardization
Hi,
Saptzae @ # 592
This cooperation would be useful not just for aviation.
This idea brings Synergy to an important element practically all designs require: Electric energy storage.
Aspects like safety, management, monitoring, interface to Systems (data), etc. would be addressed with common interests.
Apologize not participating more closely to the technical discussions. The idea to have pressure sensors in each cell (+ temp.) would provide means to safer operation.
The charger i am working has series (1 C) for high current and parallel (< 0,05 C) for low current. And NO SOFTWARE for cell voltage management. Other details will discuss by PM. Mulling a patent app for.
Saptzae @ # 592
This cooperation would be useful not just for aviation.
This idea brings Synergy to an important element practically all designs require: Electric energy storage.
Aspects like safety, management, monitoring, interface to Systems (data), etc. would be addressed with common interests.
Apologize not participating more closely to the technical discussions. The idea to have pressure sensors in each cell (+ temp.) would provide means to safer operation.
The charger i am working has series (1 C) for high current and parallel (< 0,05 C) for low current. And NO SOFTWARE for cell voltage management. Other details will discuss by PM. Mulling a patent app for.
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On assumptions
Hi,
New batteries:
1) Maintenance free: Dozens had to be replaced prematurely
2) High MTBF: Dozens failed and 2 grounded the fleet in ~ 100,000 hours
3) Heat (cell) is not an issue: Thermal runaway created smoke and fire.
4) Safe to be located in EE bays:
In one case Logan firecrews
spent more than one hour
to control a fire. In TAK the
smoke was visible by ATC. A
non designed fuse (ground
wire) opened and probably
saved the day. (With the
prompt landing.)
5) Algorithms are capable even
to "avoid" individual cell
temperature monitoring
probes: A shorted cell
triggered a thermal
runaway. (BOS) A super
heated cell (# 3) led to a
short circuit of 12 V to
battery case as mentioned
(model) in an earlier post.
Other assumptions were made...
New batteries:
1) Maintenance free: Dozens had to be replaced prematurely
2) High MTBF: Dozens failed and 2 grounded the fleet in ~ 100,000 hours
3) Heat (cell) is not an issue: Thermal runaway created smoke and fire.
4) Safe to be located in EE bays:
In one case Logan firecrews
spent more than one hour
to control a fire. In TAK the
smoke was visible by ATC. A
non designed fuse (ground
wire) opened and probably
saved the day. (With the
prompt landing.)
5) Algorithms are capable even
to "avoid" individual cell
temperature monitoring
probes: A shorted cell
triggered a thermal
runaway. (BOS) A super
heated cell (# 3) led to a
short circuit of 12 V to
battery case as mentioned
(model) in an earlier post.
Other assumptions were made...
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[QUOTE][We who inhabit this small, damp island have to re-read it several times to confirm that it doesn't mention politicians' misdemeanours, football or breasts in the narrative./QUOTE]
If you said "she's got a magnificent pair of batteries"..you couldn't volt her.
.....sorry, couldn't resist, I blame Slasher's influence.
BACK TO BATTERIES!
@syseng...The diagram you post is very enlightening.What really jumps out at me, is the fact that this battery-pack would appear to be connected straight onto a "dirty" bus via a contactor....No filtering,no diode-protection, so the charging/monitoring circuits are in parallel woth the battery......no series protection whatsoever to protect the cells against transients ,or ,indeed, exccessive voltage on the bus....Unless i'm really thick and missing something blindingly obvious, that there's the elephant in the room.
@ Turin, yes, I understand that the electronics battery cannot be used to start the APU...but unless the RAT is defective as well (in which case "we're all doomed Captain" ) it should deploy and be producing well before the "safe " discharge level is reached on either battery.
I would think that, if the emergency was that dire that ALL power supplies were gone except a glorified car-battery (OK, a very expensive 75Ah bespoke battery) draining that extra tiny bit of power isn't going to materially alter things....in that situation, a big red switch/button to hook the APU battery to the Avionics bus may be a better last-ditch measure...(with diode/electronic protection to prevent back-feeding if the APU battery is already frazzled.)...so, what happens if the "main" battery self-destructs before/when/during , its call to duty in this "Gimli Glider"that has 4 discrete inop generating systems simultaneously?
Agreed the monitoring wires look tight and I don't buy the Vibration theory. they appear to be standard eyelet crimps and I'd have expected a decent piece of shrink-sleeve over the end support -crimp,extending a cm.or so out along the wire insulation...can't make out if the actual core is crimped or solderedbut i'd really like to see a soldered/spot-welded connection to the busbars,instead of a scabby little self-tapper.
still not impressed after reading all these posts by real engineers who really appear to understand this subject far better than me.
Thank you all, it's a fascinating subject.
If you said "she's got a magnificent pair of batteries"..you couldn't volt her.
.....sorry, couldn't resist, I blame Slasher's influence.BACK TO BATTERIES!
@syseng...The diagram you post is very enlightening.What really jumps out at me, is the fact that this battery-pack would appear to be connected straight onto a "dirty" bus via a contactor....No filtering,no diode-protection, so the charging/monitoring circuits are in parallel woth the battery......no series protection whatsoever to protect the cells against transients ,or ,indeed, exccessive voltage on the bus....Unless i'm really thick and missing something blindingly obvious, that there's the elephant in the room.
@ Turin, yes, I understand that the electronics battery cannot be used to start the APU...but unless the RAT is defective as well (in which case "we're all doomed Captain" ) it should deploy and be producing well before the "safe " discharge level is reached on either battery.
I would think that, if the emergency was that dire that ALL power supplies were gone except a glorified car-battery (OK, a very expensive 75Ah bespoke battery) draining that extra tiny bit of power isn't going to materially alter things....in that situation, a big red switch/button to hook the APU battery to the Avionics bus may be a better last-ditch measure...(with diode/electronic protection to prevent back-feeding if the APU battery is already frazzled.)...so, what happens if the "main" battery self-destructs before/when/during , its call to duty in this "Gimli Glider"that has 4 discrete inop generating systems simultaneously?
Agreed the monitoring wires look tight and I don't buy the Vibration theory. they appear to be standard eyelet crimps and I'd have expected a decent piece of shrink-sleeve over the end support -crimp,extending a cm.or so out along the wire insulation...can't make out if the actual core is crimped or solderedbut i'd really like to see a soldered/spot-welded connection to the busbars,instead of a scabby little self-tapper.
still not impressed after reading all these posts by real engineers who really appear to understand this subject far better than me.
Thank you all, it's a fascinating subject.
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@RR_NDB
You can't have one without the other.
If you are meaning a spontaneous cell short, the result is still heat, and the BMS should detect a rapid change in either temperature or cell impedance.
Heat (cell) is not an issue: Thermal runaway created smoke and fire.
If you are meaning a spontaneous cell short, the result is still heat, and the BMS should detect a rapid change in either temperature or cell impedance.
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On (wrong) assumptions certainly made during design
Hi,
mm43,
Letīs put it crystal clear:
Itīs unbelievable but it seems the designers of the battery didnīt consider cell heat. NTSB model is: Short(s) generated heat and a "positive feedback" started (the so called, Thermal Runaway) leading to the destruction of the battery with other much more dangerous cosequences like FIRE.
This as i understood is the WHAT, Deborah mentioned in first briefing. It remain the WHY. We expect this in next interim and their looking to "surounding electric environment" is a logical step in the investigation. I was concerned with the no mention of cell voltages. If this data was lost (i suspect, was) the shorts could be for more than one reason. Indeed temp.(of EACH cell), voltage, impedance are intrinsically related.
mm43,
Letīs put it crystal clear:
Itīs unbelievable but it seems the designers of the battery didnīt consider cell heat. NTSB model is: Short(s) generated heat and a "positive feedback" started (the so called, Thermal Runaway) leading to the destruction of the battery with other much more dangerous cosequences like FIRE.
This as i understood is the WHAT, Deborah mentioned in first briefing. It remain the WHY. We expect this in next interim and their looking to "surounding electric environment" is a logical step in the investigation. I was concerned with the no mention of cell voltages. If this data was lost (i suspect, was) the shorts could be for more than one reason. Indeed temp.(of EACH cell), voltage, impedance are intrinsically related.