That's alright. :)

To me it does not seem possible to do LiPo without, as the compounding imbalance will destroy the cells. http://focus.ti.com/download/trng/do...0and%20How.pdf

Edit: And there is an example with switch mode to pump power between cells.

saptzae:

Clever. I was assuming resistive cell balancing, but switched capacitors
would get the job done in a much smaller volume. So they are probably
doing cell balancing on one of those boards...

Regards,

Chris

Parallell charging SHOULD be adopted
 

Hi,

I will post ASAP the block diagram of a PARALLEL CHARGING WITH BITE designed during the last days.

All considerations like cost, reliability, MANDATORY K.I.S.S. approach, etc. was taken into account.

The use of SERIES CHARGING (evident from the pictures) to a battery with adjacent cells (thermally speaking) is imho a recipe for problems.

The location of the batteries in close vicinity to electronic modules and THE PLACEMENT OF TWO DENSE PCB´S in the same chamber of the cells SUGGEST the DECISION MAKING ON USE OF Li Ion was based on:

CELLS WIL NOT FAIL, WILL NOT go to THERMAL RUNAWAY AND BATTERIES WILL BETTER THAN PREVIOUS "STANDARDS" (Ni Cd).

This imho an ERROR, was partly made in "high rocks" of Boeing as we can imagine.

Sad and concerning.

PS

Parallel charging can be done with the cells connected in series. Additionally you may be able to "help" a less capable cell to deliver when battery is being used (as we know, rarely). Imagine 8 (identical) circuits (5 Amps avg, 20 Amps max) connected (floating, obviously) directly to ea. cell).
You can balance easily, manage and incorporate a very capable BITE to track cell performance)

saptzae:
Even my own limited experience with li suggests 100's of charge discharge
cycles and that's in consumer product. I know the lead acid gel batteries
that the telcos use have a 10 year design life and the earlier wet cells 20-30
years, even if that is under float conditions...

Regards,

Chris

mix of replacement reasons
 

That story is evolving this morning. A Seattle Times article quoted a Boeing source at more than 100 replacements. However, many of those are for reasons other than observed premature discrepant behavior in service.

Somewhere on those PCBs lives a function that "locks out" usage of the battery if it is excessively discharged, which then must be removed and returned to GS Yuasa. Apparently there are inadvertent operational errors somewhat akin to you or I leaving the dome light on in an older car which can trigger this removal reason. They also lock themselves out if "improperly disconnected", whatever that means. Another cause is going past the allowed age limit (remember that a lot of these hulls must have had their first batteries installed years ago).

While that may well bargain the hundred down to a much lower number of genuine interest to us, it obfuscates the question of how many genuine in-service discrepancies were seen. And the Boeing excuse list would not seem to cover those three reported cases in which the charger was changed along with the battery. Mis-diagnosis? Real problem?

I harbor a suspicion that somewhere in the removals is the signature of a genuine problem related to the major incidents, but that is just a mildly informed guess. I hope Boeing engineering is mining that data source more energetically than Boeing PR is trying to make it look OK.

Computing a component's suitability also depends on dependability.

Likewise cycles/time. If the suggestion from Boeing is that frequency of unsuitable performance issues were not somehow addressed ad nauseum in the certification process, they are smoking other than Lithium Cobalt Oxide.

There is no reasonable explanation for FAA not to know about the replacement rate in service. None. If it was logged, they know. If not, some one or other or many are in very deep doo doo.

SPOT ON!

I fully agree.

hetfield...

But that is not the case, the special language in the regs allow for fire, loss of electrolyte, and venting of toxic (hot) gases,

That means the materials encased were sacrificial, by definition. No consideration of isolation (engineering) was considered, if it was, it was rejected.
These are deliberate decisions, not blunders....

Do T7 have Li-Ion batteries?

I think many people are losing the sight of an important fact.

The CELLS are Japanese
The Charge/discharge regulators are American.
The Assemblers are French..they make "the battery"!

the whole "box of tricks" "SHOULD" be an integrated "plug 'n'play" fitment , fully self-contained ,to hook straight onto the hookup wires and perform

Clearly it doesn't. the fault lies in the Thales -supplied "Electricity reservoir box"

WRT charge/discharge.....APU should be started off bus fed by 4 main gen's before shut-down....APU feeds all demands in conjunction with main Gen's until engines are shut down.
IF Apu is shut down for ANY reason, the aircraft is then dependent on an outside GPU for the next half-hour ,before the APU can be started again. As soon as the main engines are restarted (GPU?) the power is restored, but temperature/time limitation means that the APU will be inop, under these conditions, for takeoff.

Even if the APU is off, and all gen's fail, there's STILL the RAT to supplement the main battery (which only needs 5 minutes reserve)....under those circumstances, the F.D. cerw will have a lot more to worry about than wether the APU has cooled sufficiently for a restart :}

There is little doubt that there is adequate redundancy and capacity in the system,- even with a U/S APU battery,the APU has 2 alternative starting-modes....so the circle completes......
The components in the Thales-assembled Battery do not perform as a safe, integrated ,rechargeable source of stored electricity.

IMHO, individual cell charge/discharge is inadequately controlled/monitored.

The fact that a marginally -safe technology is used , certainly doesn't help! :eek:

@cockney steve

What about the important BMS, built by "Kanto Aircraft Instrument"?

archae86:
Great info, thanks.

That's starting to give me feelings of dejavu, in that it's increasingly
common for equipment of all types to have no locally servicable parts.
The only recourse being to have the kit returned to the vendor, or their
designated agencies. Even where local servicing may be possible, service
information is often denied and it's designed to create an expensive
monopoly for the sole benefit of the vendor. In this case, why must the
battery go back to Yuasa and not the system integrator ?. At least, local
agencies should be able to interrogate the battery data log to determine
the detailed cause of the fault and thus eleminate spurious shutdowns due
to overzealous or faulty built in test.

Thats adds more weight to something discussed in a previous post, where I was
trying to work out why the data log for the burnt out battery appeared
to be unavailable. The suggestion was that the boards in the enclosure were
responsible for the data logging, (with good reason) and logged the whole life
of the battery. Because of board damage, the logged battery data would likely
be irrecoverable and make cause of failure very difficult to determine...

Regards,

Chris

Where components are made does not really matter (to me).

That several distributed suppliers must be integrated does not help. However, this is just "normal".

Concur, at the system level.

Concur

Right, but are ladders more than marginally -safe?, after all, one can fall down :confused:

What matters is management. That known deficiencies (10 bat's out of 30 replaced at ANA ) were not addressed in time is "not uncommon" mismanagement. Would they have been proactive, they could have started what the NTSB does now after the first three failures, and the fleet would not have been grounded.

That's what I am here for, to learn.

No, but they have corrosive alkaline and alu eating electrolyte, can overheat and short and boil, spilling the electrolyte all over.

My point is that the basic architecture is the same, implementation is common practice in aerospace.

And my point is, do not put a BMS into a case where a "thermal runaway" (Li-Ion) may happen...

@RR_NDB

Looking forward, I provide a free review.

@archae86
Sorry, 10 out of 30 at ANA is plenty to wake up to,with plenty of time. :=

saptzae:
Agreed. Anyone who's lifted the lid of a nicad after brisk charging will see
evidence of electrolyte and the fumes to go with it.

In this case, I wonder if the so called fan in that enclosure is there for cooling, or primarily to exhaust the corrosive gases ?.

Electronics and cells of any type don't mix and just because it's common practice,
doesn't mean that it's correct, nor that it isn't just wrong by design :ugh:. Everyone
else does it, so it must be ok, right ?.

Designers must question everything, especially their own assumptions and those of
the people they most respect...

Regards,

Chris

@syseng68k
Cooling, one would not want to exhaust alkaline gases into an alu fuselage.

As to the gases, like with Pb, it's primarily hydrogen/oxygen, which this poster learned in his early teens, when a car battery blew up in his night desk after being _accidentally_ shorted. (head light makes a good reading lamp).

Engineering practice generally has a sound basis. For example, practically every modern LiPo battery has electronics for balancing integrated.

Right, against convenience, one should not make assumptions at all, because assumption is the mother of _all_ failure.

See, think, validate goes both ways. We have still not seen all the facts and can not make assumptions on changes before understanding the cause.

First, according to the securaplane website, battery history is recorded by the chargers - not the BMS co-located with the battery cells.

(We've been dispelling this myth every other day as someone who hasn't done due reading brings it up again and others in the same state accept it as fact.)


Next, once a cell enters thermal runaway, the job of the BMS has officially ended once it orders the final disconnect of the pack - there is nothing more it can do as the pack is headed for failure at that point.

(It's worth noting that this, too, apparently worked as advertised as there was a "drop to near zero" recorded on the batt of the ANA aircraft.)


Putting the BMS inside the battery case makes it easier to calibrate and more reliable. You are dealing with DC levels into the millivolts, and at these low voltages even the best connectors can add undesired and unpredictable resistance.

Since the BMS isn't recording history, nothing is really lost if it gets badly degraded when a battery does a thermal runaway.

@rottenray

Fully concur, thank you :ok: