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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 30th Jan 2013, 02:29
  #281 (permalink)  
 
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RR NDB:

The cells are charged serially? I thought early on i read that the cells are charged, voltage and temp monitored, individually. i.e. in parallel.

Have a bunch of closely stacked cells being fast charged and discharged in series seems like it would be a really bad design. If for no other reason than hot or cold soaking overnight, then cranking the APU, then fast charging it again, would cause huge temperature variations from the center of the battery to the outside cells, unless there was active cooling, which there is not.

Just asking. Are the cells charged and monitored serially or in parallel?

I do think Lithium is the best battery for the job. It just needs to be done right.
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Old 30th Jan 2013, 02:33
  #282 (permalink)  
 
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glenbrook, Hi

I could have been more clear; the post was meant to be somewhat tongue in cheek. It was (is?) Boeing's position that the rules were honored, that the grounding was a timid reaction to pressure from the political side.

They have a point, the fire was contained withn 20 inches of the case, no damage to nearby equipment, venting worked, etc.

But it is too late to unground... Boeing is keeping their screaming profanities behind closed hatches.

cheers
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Old 30th Jan 2013, 03:23
  #283 (permalink)  
 
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Radken

Machinbird

Ahh, yes. I stand corrected. Thought about checking my facts but failed to follow up.

Some say these Li's are a mature product now. They should be, and I guess Boeing was counting on that being the exact case when the 78 elec design was finalized and flt testing later supported that conclusion. What a shame all this has now come up and spoiled the debut of this unique, and what will be one day, great aircraft.
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Old 30th Jan 2013, 03:38
  #284 (permalink)  
 
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many ANA removals

The New York Times website currently shows as part of their January 30, 2013 content a story which leads with some details of (apparently for cause and unscheduled) removals of battery packs in the ANA fleet in the months before the recent unpleasantness.

This link is quite likely to a point behind their paywall, but even so may be useful to some of you who subscribe.

NYtimes battery removal article

It says that ten batteries were replaced. It mentions that in three cases the charger was replaced along with the battery. It quotes a GS Yuasa spokesman as stating that battery exchanges are part of normal aircraft operation, but gives no data from any source to provide context on whether this removal rate should be considered unusually high save for the GS Yuasa comment and a Boeing comment that the batteries were not lasting as long as intended.

This is hardly proof, but to my eye is an additional suggestion that the actual operational environment on the aircraft is not compatible with the actual battery packs as delivered. A (rather distant) analogy might be the way certain socket locations on certain aircraft have been known to exact a severely reduced lifetime from incandescent bulbs because of excess vibration.
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Old 30th Jan 2013, 06:00
  #285 (permalink)  
 
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WSJ Article

This past day (Tues) the Wall Street Journal reported on its front page that an industry standards organization (unnamed on front page) had disagreed with Boeing on the choice of battery then being considered for the 787. WSJ reported Boeing as saying that the organization did not appreciate the high level of Boeing expertise in this area, or words to that effect.

OE
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Old 30th Jan 2013, 08:47
  #286 (permalink)  
 
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The cells are charged serially? I thought early on i read that the cells are charged, voltage and temp monitored, individually. i.e. in parallel.

Have a bunch of closely stacked cells being fast charged and discharged in series seems like it would be a really bad design. If for no other reason than hot or cold soaking overnight, then cranking the APU, then fast charging it again, would cause huge temperature variations from the center of the battery to the outside cells, unless there was active cooling, which there is not.

Just asking. Are the cells charged and monitored serially or in parallel?
@USMCProbe

Have a look to the pictures.
You will clearly see that the cells are put in serial. The thin wires at the joints come from the BMS which BALANCE charging current and monitor each cell.
So charged in serial, but adjusted individually.

Battery balancing - Wikipedia, the free encyclopedia






To put the BMS in the same case beside the cells, is not a good idea IMHO...
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Old 30th Jan 2013, 09:01
  #287 (permalink)  
 
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So charged in serial, but adjusted individually.
Looking at the massive connector bars and the tiny wiring, by which percentage can individual charging be adjusted? And what is the "industry standard" with respect to individual charge adjustment, what does for example a Prius battery do?
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Old 30th Jan 2013, 09:09
  #288 (permalink)  
 
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Looking at the massive connector bars and the tiny wiring, by which percentage can individual charging be adjusted?
Yep, good question.

I hope, it's not a design flaw....
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Old 30th Jan 2013, 11:20
  #289 (permalink)  
 
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Many Battery removals

Ten batteries were replaced at ANA after failing, more at JAL. Any info on other carriers?

This is highly unusual, more so as charge end appears to be very conservative at 4V.

4.1V-4.2V charge end is common in consumer and industrial applications.

Every 100 mV above 4V induces four times the stress, it gets worse above 4.3V though.

At 4V, these cells should last a very long time, many years.

The failed batteries must have been examined. Mighty strange that nothing seems to have been done about it.

@Volume
Less than 5%/3A max, was discussed from:
http://www.pprune.org/tech-log/50569...ml#post7656754
through:
http://www.pprune.org/tech-log/50569...ml#post7658425
and the next 10 or so posts
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Old 30th Jan 2013, 11:52
  #290 (permalink)  
 
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Quote from USMCProbe (my bold):
"Have a bunch of closely stacked cells being fast charged and discharged in series seems like it would be a really bad design."

Am currently pretty much out of my depth in this erudite, fascinating discussion. However, I cannot see how discharging the APU battery cells in parallel could provide enough "oomph", at about 4V, to start the APU.

As I understand it, the likes of RR_NDB are currently trying to work out how, in principle, the charging might be done in parallel?

Last edited by Chris Scott; 30th Jan 2013 at 11:55.
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Old 30th Jan 2013, 12:02
  #291 (permalink)  
 
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Looks like more data is coming to light.

http://www.nytimes.com/2013/01/30/bu...anted=all&_r=0

The various regulations on the design of aviation batteries, posted elsewhere, seem clear to me and what I would expect, so the problem seems to be something fundamental in the battery type and behaviour over the full temperature operating range; or the behaviour of the battery, charger, and various loads as a combined system over the full temperature operating range.

Earlier there was a mention of Testability which in simple terms is the designed means to test the full parameters of a system and simulate the operational environment in which the system will live.

I'd be interested to know the range of operating temperatures within the EE bay and APU battery location from 37,000 ft ASL to sitting on the ground, the external ambient temperatures, and anything that could influence those temperatures in the EE bay/APU battery locations.

I would then want to know when loads are placed on the battery and the timings of that in the knowledge of the changing temperatures from ground to flight levels and vice versa. The batteries that haven't failed yet might have some of that data.

Presumably there is a test rig for this system that does some of this.

I'm sure that professional organisations working on this problem are equally interested.
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Old 30th Jan 2013, 13:41
  #292 (permalink)  
 
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saptzae:

The failed batteries must have been examined. Mighty strange that nothing seems
to have been done about it.
The number replaced struck me as being rather odd as well. Why didn't this
raise concern ?. That level of replacement might suggest a problem in the
overall system design; pack temperature control in service, or perhaps vibration
related, though batteries failed in different locations.

The data sheet I have doesn't say how many charge / discharge cycles can be
expected. Perhaps you have some typical figures ?...

Regards,

Chris
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Old 30th Jan 2013, 14:02
  #293 (permalink)  
 
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Weakest link

@Chris Scott
Quote from USMCProbe (my bold):
"Have a bunch of closely stacked cells being fast charged and discharged in series seems like it would be a really bad design."
All that works for the better part of 100 years, in every vehicle with an electrical system, including aircraft and submarines, as well as with big stationary 48V telco batteries and data center UPS installations. LiPo powered vehicles deserve special mention.

All those are serially charged and discharged. Balancing by bypass is used in all large installations, except NiCd perhaps, not sure there.

I think OP was referring really to the closely stacked cells, which probably is one of the weaker links in this system. Fortunately the box held up, although barely, but it did. Practical battery management is weaker still.

IMHO the weakest link so far is the response to those 10 batteries ANA had to replace. Alarm bells should have gone off no less than after having swapped 10 Engines.

I guess electrical systems must be harder to understand than turbines.

Shades of gray without black and white answers.
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Old 30th Jan 2013, 14:25
  #294 (permalink)  
 
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Chris Scott:

As I understand it, the likes of RR_NDB are currently trying to work out how, in
principle, the charging might be done in parallel ?.
It's debatable if there would be any advantage, since better methods exist to
ensure that groups of cells in series are charged and balanced correctly. The
disadvantage is that to do it, you would need high current multipole relays
to switch all the cells from series to parallel configuration. As far as I know,
it's never done that way, either in industry, aviation or anywhere else. The cost
and weight penalty would be prohibitive. It would also mean that the battery
would be offline when charging, since the voltage would then be 4v, not the 32v
required.

For the 787 battery, all the cells are hardwired in series, charged and discharged
in series. What we know thus far is:

1) Cells are organised in series, with cell to cell connections via flat metal straps
bolted to the cell terminals. This is standard practice.

2) Cells are charged in series and there's no evidence of a separate charge circuit
per cell. For 8 cells, it would require 9 high current cables from the charger
and there are only two on this battery.

3) It's almost certain that each cell voltage is monitored.

4) It's not clear if there is a temperature sensor per cell, or one sensor for the
complete enclosure.

5) It's also not clear if electronic cell balancing is being done, though there are
probably enough wires to and from the cells to the pcb's, to do this.

Perhaps someone else can add to the above list if there's anything missing ?...

Regards,

Chris
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Old 30th Jan 2013, 14:29
  #295 (permalink)  
 
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@syseng68k

Along the lines of 4000 Cycles at 4V/80%, 1000 Cycles at 4.1V/90%, 250 Cycles at 4.2V/100%, 50 Cycles at 4.3V, 10 Cycles at 4.4V.

Li based cells keep almost all charge delivered. No gassing or heat. Cells age faster and faster above 90% charge (~4.1V). Above 4.2V cell deteriorates quickly. Heat develops by way of short or straight thermal runaway.

These batteries appear to be charged only 80% and not to see cycles like a phone, netbook or tesla roadster and will hardly be discharged below 60% capacity.

(Percentages and voltages may vary with technology and design)

All these batteries should last several years.

10 out of 30 bat's in a year? Ridiculous.
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Old 30th Jan 2013, 14:39
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@syseng68k
5) It's also not clear if electronic cell balancing is being done, though there are
probably enough wires to and from the cells to the pcb's, to do this.
Clear to me, two PCB's for exactly that purpose in the box. The upper for control and monitoring. The lower for balancing.

Does not seem to work as needed though, if it does, I would start looking for a hidden bypass somewhere powering the batteries.

Still, the monitoring should see and log all abnormal conditions and fire off warnings before batteries fail.
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Old 30th Jan 2013, 14:41
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IMHO not a good place to put a BMS.
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Old 30th Jan 2013, 15:01
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IMHO not a good place to put a BMS.
777 and others do the same. Even got a cooling fan.

Considering the number of connections, it is the best place to put it. Logs go to the charger and failsafe battery disconnection is also managed there, I hope.

When cells fail the PCB's (failed to) serve their purpose and are irrelevant after a few minutes of logging.

There will be a really interesting report one day.
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Old 30th Jan 2013, 15:14
  #299 (permalink)  
 
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GS Yuasa Li-ion battery cells selected to power International Space Station

GS Yuasa Li-ion battery cells selected to power International Space Station -- ROSWELL, Ga., Nov.*29, 2012 /PRNewswire/ --

Edit:
10 year design life. 16 cycles per day (50%* discharge): 58440

Guess they tune cells and charge just to 3.8V - 3.9V.

*90 min cycle with 35min eclipse, varies with load.

Last edited by saptzae; 30th Jan 2013 at 15:49. Reason: Calculations
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Old 30th Jan 2013, 15:42
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saptzae:

Clear to me, two PCB's for exactly that purpose in the box. The upper
for control and monitoring. The lower for balancing.
Not convinced :-). Normally, in projects where there is a mix of digital
and measurement quality analog electronics, the analog and digital
sections are separated onto separate pcbs, or the analog sections are
enclosed in screening cans to reduce digital noise. That would suggest
that the board nearest the cells is for the analog and the lower board
handles the digital. The fact thet there are several larger pin count
devices on the lower board suggests digital logic, possibly memory or
microprocessor class devices.

The other point is w/regard to the bypass, where worst case of 10w per
cell needs to provided for. Even using switch mode tech, you still
have to dissipate that power somewhere and there's little evidence of
parts to do this on the boards.

Still, the monitoring should see and log all abnormal conditions and
fire off warnings before batteries fail.
Agreed - the data log for the battery would be logically the first place
to look for the events that led to the failure, but where is it and
why wasn't this escalated back up the chain to Boeing ?. Such a
battery replacement rate should have been noticed at some level...

Regards,

Chris

Last edited by syseng68k; 30th Jan 2013 at 15:47.
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