Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

787 Batteries and Chargers - Part 1

Tech Log The very best in practical technical discussion on the web

787 Batteries and Chargers - Part 1

Old 27th Jan 2013, 18:26
  #201 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 78
Posts: 1,460
Question

After looking at the picture of the exemplar battery in the NTSB report, one thing puzzles me about the smaller monitoring wires. There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction.

One on a cell connector on one side of a battery cell, one on the interconnector that connects to the next cell, and one on the cell connector on the other side of of the interconector. (Hope that is clear)

I cannot believe that these wires are all measuring potential. Some of them are either shunt wires or serving some other function such as temperature monitoring (although how that might happen is not obvious)

Last edited by Machinbird; 27th Jan 2013 at 18:31. Reason: add hyphen
Machinbird is offline  
Old 27th Jan 2013, 18:27
  #202 (permalink)  
 
Join Date: Jun 2009
Location: Oxford, England
Posts: 297
Lyman

Boeing demonstrated no need for the Lithium Battery
I'm not sure about that. I read somewhere else that there is system / operating
requirement that the APU battery be fast charged over a time scale and at a rate
that would not be possible using lead acid or nicad.

Engineering of this type has nothing to do with emotion, seduction etc, other
than the usual designer's passion to do the job right :-).

Who knows what we will be told though. With so many $ at stake, some of the
vendors could be bankrupted if found to be at fault...

Regards,

Chris
syseng68k is offline  
Old 27th Jan 2013, 18:28
  #203 (permalink)  
 
Join Date: Aug 2011
Location: hong kong
Age: 60
Posts: 93
@Turin
The APU AC BUS can be tied to the L and R AC busses.
Thank you. That eliminates the bus as the culprit at BOS. Cause of other cells destruction is down to the charger, continuing to power the battery after failure of #3, or purely thermal.
saptzae is offline  
Old 27th Jan 2013, 18:40
  #204 (permalink)  
 
Join Date: Aug 2011
Location: hong kong
Age: 60
Posts: 93
@Machinbird
After looking at the picture of the exemplar battery in the NTSB report, one thing puzzles me about the smaller monitoring wires. There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction
Redundancy of sensing and balancing?

Edit: Upper PCB looks like for control and sensing. Lower PCB for balancing. Seems to be a lot of electronics for this functionality.

Last edited by saptzae; 27th Jan 2013 at 18:45. Reason: PCB
saptzae is offline  
Old 27th Jan 2013, 18:42
  #205 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 876
Hi, cwatters (#199)

I yet expressed my concern on the max current the main battery is alowed to supply the DC bus. In an earlier post we discussed the issue.

Points to mention:

1) As confirmed by TURIN there is a diode module easily understood as the switch that put the (charged) battery in the bus. I agree with your concern that a limiter is important. I consider ESSENTIAL when using these dangerous batteries, lets say, DANGEROUS CELLS. Even with superb circuitry they will remain DANGEROUS.
2) A limiter to be safe must be integrated to the System Software (unless you put a FE in the cockpit). Which are the priorities when the bus needs the help from the (main) battery?
3) As i understand the Battery charger is connected BETWEEN the battery and the diode module. The management of the best configs in a degrading scenario is not so simple.
4) And you must always respect the weakness and criticality of the dangerous cells. Who in the project made the algorithms ? (required and certainly existent). Boeing or a partner?

Integration teething pains? Or nightmare?
RR_NDB is offline  
Old 27th Jan 2013, 18:51
  #206 (permalink)  
 
Join Date: Jun 2009
Location: Oxford, England
Posts: 297
Machinbird

After looking at the picture of the exemplar battery in the NTSB report, one thing puzzles me about the smaller monitoring wires. There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction.
There was a brief explanation in post, #177 but put more simply, the use of
two wires to each cell isolates that cell measurement from any interaction with
the other cell voltages and currents.

Also, wires may be dualled in some places to provide redundancy against a
single wire break. This would also allow diagnostics to detect a broken wire.
Such dualling is not uncommon...

Regards,

Chris
syseng68k is offline  
Old 27th Jan 2013, 18:53
  #207 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 876
Redundancy?

Hi,

Machinbird (#201)

Redundant wiring...

What the designers made is still beyond my imagination.

The thin wires, over the cells, the connectors used and TWO PCBs all inside the chamber where the hot cells are is UNBELIEVABLE.

Last edited by RR_NDB; 27th Jan 2013 at 18:56. Reason: Typo and add title
RR_NDB is offline  
Old 27th Jan 2013, 18:59
  #208 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,123
syseng68k

Quote:
Boeing demonstrated no need for the Lithium Battery? (sorry, my quote)

You reply...I'm not sure about that. I read somewhere else that there is system / operating requirement that the APU battery be fast charged over a time scale and at a rate that would not be possible using lead acid or nicad.

And, they would not have. If FAA requires a performance level that cannot be met with current technology, then they have gone into the design business. And Boeing would not design an aircraft that could not be built under current regs. Would they build a bird that was dependent on concurrent rule change? No, the rule predated the design...

If that is the case, the Dreamliner is dead. It is at least cemented in concrete to Lithium....because without back up electric, no current a/c can be airworthy. And if 787 won't certify with anything but Lithium.....

Maybe the bridge back to NickelMH burned in the EEbay?

Last edited by Lyman; 27th Jan 2013 at 23:19.
Lyman is offline  
Old 27th Jan 2013, 19:04
  #209 (permalink)  
 
Join Date: Jun 2009
Location: Oxford, England
Posts: 297
What the designers made is still beyond my imagination.

The thin wires, over the cells, the connectors used and TWO PCBs all inside the chamber where the hot cells are is UNBELIEVABLE.
...yes and if the battery data logging is on those boards as well, then the audit trail
for the death of the battery is lost forever

How that ever got past systems engineering beats me...

Regards,

Chris

Last edited by syseng68k; 27th Jan 2013 at 19:04.
syseng68k is offline  
Old 27th Jan 2013, 19:13
  #210 (permalink)  
 
Join Date: Aug 2011
Location: hong kong
Age: 60
Posts: 93
@RR_NDB

The thin wires, over the cells, the connectors used and TWO PCBs all inside the chamber where the hot cells are is UNBELIEVABLE
As to electronics in the same box, I prefer this over adding another box. The wiring to it could not practically be protected.

I am still trying to understand the failures.

Could one make the thing simpler and thereby safer? Perhaps.
saptzae is offline  
Old 27th Jan 2013, 19:21
  #211 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 876
Battery voltage measurement

Hi,

On the 6 wires attached to ea. one battery terminals (strips) we may comment:

1) They measured the voltage in the best circuit points. Inside the battery and directly at cells
2) Redundancy may explain half of the wires (triple) with a voting scheme.
3) Other 2 (1 in ea. strip) could be to simplify the measurement of the adjacent cells voltage (near to minus and plus battery terminals)
4) The remaining two could be the mentioned bypass.

IMHO the matching using bypass is not the best way as emphasized when comment on much safer parallel charging.

Last edited by RR_NDB; 27th Jan 2013 at 19:24. Reason: Typo
RR_NDB is offline  
Old 27th Jan 2013, 19:28
  #212 (permalink)  
 
Join Date: Jun 2009
Location: Oxford, England
Posts: 297
saptzae:

As to electronics in the same box, I prefer this over adding another box.
The wiring to it could not practically be protected.
In fact, you don't need another box. There's already a multipin connector
back to the charger and one would expect the battery sensing and management
electronics to be in the charger enclosure, not at the battery, where it's
vulnerable to cell leakage.

Imho, the only things that should be in the enclosure are the cells and
perhaps a small pcb supported by the connector, carrying inline fuses to
protect critical wiring.

We just might have to agree to differ on this one, but it all helps the
enquiry :-)...

Regards,

Chris
syseng68k is offline  
Old 27th Jan 2013, 19:39
  #213 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 876
Same box separated chambers

Hi saptzae,

They could use separated chambers. The sensing AND the preprocessing of the voltages and temperature as you know is highly CRITICAL. The connectors used inside the same enviroment is a weak point. The harness (testability) another issue.

The failure of both batteries perhaps can be explained by the only thing common in both incidents. The battery itself. Heat and electrolyte leakage conpromising this circuitry not adequately located.
RR_NDB is offline  
Old 27th Jan 2013, 19:48
  #214 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 876
Hi,

Chris @ #209

Indeed. We can strongly suspect we lost the information. Why?

If the measurement is conpromised (as happens in Pitot icing) the recorded parameters are useless.

We will need better ways to monitor these Dangerous Cells in order to allow the to be used in airliners.

Still LOLng on the "999% required"
RR_NDB is offline  
Old 27th Jan 2013, 20:36
  #215 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 77
Posts: 1,330
Originally Posted by syseng68k
Imho, the only things that should be in the enclosure are the cells and perhaps a small pcb supported by the connector, carrying inline fuses to protect critical wiring.
I suspect the reason for the present arrangement is to keep the battery management system intrinsic with the cells that it controls. Additional and unquantifiable ohmic losses could present a significant problem for remote monitoring.
mm43 is offline  
Old 27th Jan 2013, 21:21
  #216 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 876
Remote sensing

mm43, (# 215)

With the "guarding" config (Kelvin bridge) and other alternatives you can do it precisely and reliably very far.

Regards,
RR_NDB is offline  
Old 27th Jan 2013, 21:35
  #217 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 876
Ni Cd

Bear @ #208

The retrofit to Ni Cd is (technically speaking) ABSOLUTELY POSSIBLE.

Problem is problems are mounting and the technical aspect is one among other.

The Review is IMO the major issue.

A virtual stalemate was created with the threat to make everybody loose.

And the chances to precisely identify what led to BOS fire and TAK smoke are not 100%

Last edited by RR_NDB; 27th Jan 2013 at 21:38.
RR_NDB is offline  
Old 27th Jan 2013, 21:53
  #218 (permalink)  
 
Join Date: Mar 2006
Location: Choroni, sometimes
Posts: 1,975
I'm afraid, no RC jockey would buy a LiPo battery with this architecture for a 100 USD modell plane.
hetfield is offline  
Old 27th Jan 2013, 22:44
  #219 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 81
Posts: 1,689
Originally Posted by Machinbird
There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction.
Yes, and there are 7 such inter-cell junctions. There are also 7 wires at each of the two remaining battery terminals. That seem to be all 35 wires of the visible battery harness in that picture. So where are the temperature sensors?
HazelNuts39 is offline  
Old 27th Jan 2013, 23:03
  #220 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,123
RR_NDB

Possible in every way but one? If Boeing utilizes the Licell pursuant to the "waiver" (the 'restrictions') because their design cannot accomodate NiMH, then they cannot even propose it.

They then sink or swim with LiPolymer. To do that, they must redesign the entire technology. They then have to show, against existing prejudice and accident history, that LiPolymer is safe, to a degree established by the authority that put them on the ground.

Why are the cells wrapped rectangularly? From a geometric standpoint, why not cylindrical? Flattening a two phase material roll creates build at the edges, and ooze at the ends. Why conductors at the top, not the side? Why stacked chock a block in a cube, instead of nested in a "honeycomb, horizontally? Why then a conductor for a case, and not a cast ceramic vault?

A thin layer of plastic to isolate the looms from solid metal conductors, so the insulation fails, and the sensing and control looms all short together?

A lash up, suitable for Mickey Rooney's soap box racer?

Last edited by Lyman; 27th Jan 2013 at 23:21.
Lyman is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.