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.:confused:
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) |
Lyman
Boeing demonstrated no need for the Lithium Battery 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 |
@Turin
The APU AC BUS can be tied to the L and R AC busses. |
@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 Edit: Upper PCB looks like for control and sensing. Lower PCB for balancing. Seems to be a lot of electronics for this functionality. |
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, let´s 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? |
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. 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 |
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 PCB´s all inside the chamber where the hot cells are is UNBELIEVABLE. |
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? |
What the designers made is still beyond my imagination. The thin wires, over the cells, the connectors used and TWO PCB´s all inside the chamber where the hot cells are is UNBELIEVABLE. for the death of the battery is lost forever :eek: How that ever got past systems engineering beats me... Regards, Chris |
@RR_NDB
The thin wires, over the cells, the connectors used and TWO PCB´s all inside the chamber where the hot cells are is UNBELIEVABLE I am still trying to understand the failures. Could one make the thing simpler and thereby safer? Perhaps. |
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. |
saptzae:
As to electronics in the same box, I prefer this over adding another box. The wiring to it could not practically be protected. 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 |
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. |
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 LOL´ng on the "999% required" |
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.
|
Remote sensing
mm43, (# 215)
With the "guarding" config (Kelvin bridge) and other alternatives you can do it precisely and reliably very far. Regards, |
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% |
I'm afraid, no RC jockey would buy a LiPo battery with this architecture for a 100 USD modell plane.
|
Originally Posted by Machinbird
There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction.
|
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? |
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