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Battery BMS failures?

 
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kenryan



Joined: 20 Oct 2009
Posts: 324

PostPosted: Mon Mar 18, 2019 7:41 am    Post subject: Battery BMS failures? Reply with quote

On the Aircraft Spruce page for the Aerovoltz battery, under the "Overview" tab, the following text appears:

"An Aerovoltz external BMS is in a prototype stage and will be made available to all Lithium Battery owners in the near future. Putting the unit internally dramatically drives up the battery cost and all batteries will wear out eventually so making it external will keep the cost of ownership lower down the road when it comes time to replace.
The current BMS systems on the market are very sensitive to damage and it can disable a perfectly good battery that will then need replacing. We don’t feel that’s fair to our customers."
Has anyone heard about a rash of BMS failures?


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PostPosted: Mon Mar 18, 2019 9:48 am    Post subject: Battery BMS failures? Reply with quote

Quote:

Has anyone heard about a rash of BMS failures?

Good catch Ken. I'd be interested
(as would we all) in knowing what
kind of BMS failures have occurred.

Unfortunately, every battery failure
I've tried to follow up with the
manufacture was greeted with a stone
wall . . . take that back . . . used
to get great data dumps from Skip
Koss on Concorde product issues.

I've asked to be the recipient of any
failed batteries (or other devices)
so that I might disassemble for close
examination in a quest for answers . . .
but those opportunities are rare
to non-existent.

The outcome of non-communication is
ignorant assumption which gets traded
around the various venues . . . with
demonstrable data creep.

The first difficulty we have is defining
"Battery Management System". Many
lithium cylindrical cells are fitted
with dead short mitigation and are
advertised to be fitted with a "BMS".

Batteries and array of series-parallel
cells might include a cell balancing
module and advertised to include
a built-in "BMS".

Then there are full-up BMS like EarthX
and True Blue that will manage overheat,
over volts, charge balance/limiting,
fault mitigation and, in True Blue
case, comfortable management of vented
gasses in case the unthinkable does
happen.

Unless we're favored with a published
product performance specification for
the failure being studied, any assertions
about 'BMS failure' are exceedingly short
on useful data.

Keep your ears to the ground guys . . .
we might get lucky . . .





Bob . . .


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echristley(at)att.net
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PostPosted: Mon Mar 18, 2019 4:47 pm    Post subject: Battery BMS failures? Reply with quote

I have heard about the desulfater (sp?) charges killing the electronics due to their large voltage spikes. The battery manufacturers themselves warn about those.
Otherwise....nada.


On Monday, March 18, 2019, 11:42:05 AM EDT, Ken Ryan <keninalaska(at)gmail.com> wrote:




On the Aircraft Spruce page for the Aerovoltz battery, under the "Overview" tab, the following text appears:

"An Aerovoltz external BMS is in a prototype stage and will be made available to all Lithium Battery owners in the near future. Putting the unit internally dramatically drives up the battery cost and all batteries will wear out eventually so making it external will keep the cost of ownership lower down the road when it comes time to replace.
The current BMS systems on the market are very sensitive to damage and it can disable a perfectly good battery that will then need replacing. We don’t feel that’s fair to our customers."
Has anyone heard about a rash of BMS failures?


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PostPosted: Tue Mar 19, 2019 12:34 pm    Post subject: Battery BMS failures? Reply with quote

On 3/18/2019 12:47 PM, Robert L. Nuckolls, III wrote:

Quote:
[snip]
Then there are full-up BMS like EarthX
and True Blue that will manage overheat,
over volts, charge balance/limiting,
fault mitigation and, in True Blue
case, comfortable management of vented
gasses in case the unthinkable does
happen.

Unless we're favored with a published
product performance specification for
the failure being studied, any assertions
about 'BMS failure' are exceedingly short
on useful data.

Keep your ears to the ground guys . . .
we might get lucky . . .





Bob . . .
Bob,

Speaking of BMS, perhaps you can explain (since EarthX seems unable) why EarthX batteries, with their 'full BMS', have a limit on alternator current capability based on their battery capacity. I am unable to see why a BMS that can manage individual cell charging, and protect individual cells plus the entire battery, is unable to limit overall charge current to the battery to a safe level. I've repeatedly asked that question of their spokesperson on the VAF (RV) forum, and gotten words without answers.

Charlie
Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]


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PostPosted: Wed Mar 20, 2019 7:15 am    Post subject: Battery BMS failures? Reply with quote

Quote:
Bob,

Speaking of BMS, perhaps you can explain (since EarthX seems unable) why EarthX batteries, with their 'full BMS', have a limit on alternator current capability based on their battery capacity. I am unable to see why a BMS that can manage individual cell charging, and protect individual cells plus the entire battery, is unable to limit overall charge current to the battery to a safe level. I've repeatedly asked that question of their spokesperson on the VAF (RV) forum, and gotten words without answers.

Charlie

Interesting question . . .

I've oft asserted that batteries are
like houseplants. Given the right treatment
in proper proportions and protected from
deleterious stress, they will 'bloom'
and thrive.

But the term 'battery' is not quantified
and the selection of a battery is to
craft a kind of marriage between a host
of players not the least of which are
the engine driven power source(s) and
design goals for normal and abnormal
operations.

Lithium cells are the orchids of the
battery family . . . capable of extra-
ordinary performance in some respects
but exceedingly sensitive to
stress largely tolerated or
shrugged off by the likes of
Flooded, SVLA, gell and NiCad
technologies.

Lithium is extra-ordinarily vulnerable
to over and under voltage conditions.
Hence the 'real' BMS will strive to
operate the array of cells between
about 20 and 90 percent of charge.
This is a goal stated by the electric
and hybrid car folks. No doubt, EarthX
has their own numbers but what ever
the numbers, ignoring them risks
premature battery failure.

Then there's temperature . . . stuffing
energy back into a lithium array
MUST raise the chemistry's temperature
as does prolonged heavy rate discharge.
So the agile BMS watches temperatures
and strives to limit those effects
on the cells irrespective of system
demands from the outside.

External hard faults cause spectacular
current flows with a new constellation
of risks for catastrophic failures.
A BMS tailored for engine cranking
expects to see some really high
current flows for short periods of
time . . . but it must differentiate
between starter inrush/engine spin-up
and a hard fault.

I've mentioned that the enclosure
for a True Blue, TC/TSO battery
is filled with electronics . . .
electronics with agility and robustness
to accomplish all these things to
prevent premature failure while packaged
to keep the rare catastrophic failure
from migrating to the rest of the
aircraft.

True Blue batteries are used on twin
turbine aircraft with starter generators
up to and including 400A per side or
800A of recharge capability. Starter
inrush is typically 1500-2000 amps
followed by spin-up currents on the
order of 500-700A lasting 20-30
seconds. My hat is off to the folks
who crafted an array of silicon that
can operate in series with those loads
yet meet design goals for safety and
battery life.

AeroVoltz seems to be moving toward
offering an EXTERNAL BMS for their
product line . . . methinks a fine
idea. That way you don't trash a
bunch of perfectly good transistors
along with a shot battery.

The most difficult thing for a BMS
to do is throttle currents . . . in
either a charge or discharge mode.
The series connected control devices
are either switched on hard (saturated)
or totally open (off). This offers
the smallest form factor of electronics
to manage such current levels.

Battery recharge limits are largely
a thermal management issue. The
very low internal impedance of the
lithium cell COMBINED with its
low mass raises concerns for overheating
during prolonged high rates of charge.

True Blue isn't immune to these
forces either but they're designed to
work in a world of currents a magnitude
greater than piston driven light aircraft.
EarthX and contemporaries are not immune
from the need to make compromises in design
goals. They are marketing good cranking
performance and light weight. Light
weight generally brings extra-ordinary
requirements in thermal management.
Light weight and small size puts limits
on capacity . . . largely independent
of short term cranking ability.

Given the fact that a BMS cannot 'throttle'
current into or out of the battery,
they must be cognizant of the risks for
marrying their 'orchid' to a system
recently divorced from a 'bromeliad'
that may not easily bloom but it doesn't
lay down and die when insulted.

So what's the responsible supplier of
light cranking batteries to do when
marketing to relative technical
novices about the care and feeding
of their products. To be sure, lots
of their batteries are being married
to systems that already have alternators
that are too big.

If the engine starts easily when
smartly cranked time needed to recharge
is limited even if too fast. If the
operator NEVER allows the battery to
be deeply discharged followed by
an in-situ recharge by the ship's
too-big alternator . . . then risks
to the battery are low.

At the same time, the operator purchased
"light" and "whippy-starting" and made
no demands for electrical and thermal
robustness. So it makes sense that
EarthX would recommend limiting the
size of the alternator depending
on size of battery . . . not a very
realistic expectation but a good
CYA move nonetheless.

This raises a recollection of experiences
with another shotgun wedding between
poorly matched components. Waayyy
back when we got all exercised about
what was then a big quantum leap
in light weight, robust cranking
batteries with flooded NiCads.

After setting a few airplanes on fire
with a marriage of nicad and twin
turbines, powers-that=be decided
that the BEST thing to do was add
a remote reading battery temperature
meter paired with yellow warning
and red danger lights designed
to assist crews in managing their
'orchids' to prevent overheat
and thermal runaway.

I argued then that we could craft
an accessory to the starter-generator
controllers that would automatically
adjust bus voltage in response to
battery overheat. That wasn't well
received so we added another thing
on the panel that was harder to
install and drove up pilot work
loads.

The same thing could be done here.
The BMS for the alternator/lithium
marriage could easily include an
regulator that would prevent an
alternator of ANY SIZE from abusing
the battery . . . maybe AeroVoltz
will do it.



Bob . . .


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Eric Page



Joined: 15 Feb 2017
Posts: 116

PostPosted: Wed Mar 20, 2019 10:37 am    Post subject: Re: Battery BMS failures? Reply with quote

Charlie England wrote:
Speaking of BMS, perhaps you can explain (since EarthX seems unable) why EarthX batteries, with their 'full BMS', have a limit on alternator current capability based on their battery capacity. I am unable to see why a BMS that can manage individual cell charging, and protect individual cells plus the entire battery, is unable to limit overall charge current to the battery to a safe level. I've repeatedly asked that question of their spokesperson on the VAF (RV) forum, and gotten words without answers.


My guess is that it's a limitation of the cell balancing circuitry in the BMS. As a cell within the battery reaches full charge, the BMS puts a resistance across it (either a fixed resistor hard-switched across the cell or a linear-mode transistor) to burn the current that would otherwise overcharge the cell while the others continue to charge. There must be a limit to the power that this system can dissipate, which may explain the alternator output limitation.

Robert L. Nuckolls, III wrote:
After setting a few airplanes on fire with a marriage of nicad and twin turbines, powers-that=be decided that the BEST thing to do was add a remote reading battery temperature meter paired with yellow warning and red danger lights designed to assist crews in managing their 'orchids' to prevent overheat and thermal runaway.


Indeed, the deHavilland DHC-8-202 that I flew in a previous life was fitted with battery temperature gauges on the overhead panel (just below the left fire t-handle in the linked image).

https://bitly.com/2uj9V9F+

The airline I worked for operated them in the desert southwest, where ambient temps routinely exceed 100°F. Given the short-hop, quick-turn nature of the flying we did, and the eye-watering current required to start a >2,000shp engine, we kept a close eye on those gauges.

Eric


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PostPosted: Thu Mar 21, 2019 5:05 am    Post subject: Battery BMS failures? Reply with quote

Quote:
So the agile BMS watches temperatures
and strives to limit those effects
on the cells irrespective of system
demands from the outside.

Oh yeah, forgot to include charge balancing.
Unlike most battery chemistries, individual
cells in a series string of lithium may
become 'unbalanced'. This simply means that
one or more cells may 'top off' sooner than
the rest. If the charging continues until
all cells are topped off, there is risk
for over-charging the fast learners thus
insulting their sensibilities.

This is generally accomplished by placing
a load resistor across the faster cells
thus forcing more charge energy into the
slow cells until everyone is in lock-step . . .
consider a cell balancer to be the
ISO9000 of the lithium battery community.

Here's an article from Battery University
on the topic . . .

https://tinyurl.com/y3egekew

. . . yesterday's missive was intended to
illustrate that the term "BMS" is un-defined
in the consumer world and maybe not well
defined in the engineering world either. Unless you
have access to the designer's product performance
specification, it's wise to investigate
before you plunk down your beer money
for a battery upgrade. The full constellation
of products offered are NOT interchangeable
nor are they necessarily plug-n-play into
our legacy electrical systems.

In light of this fact, the phrase "BMS
failure" in any dark-n-stormy-night
story is not very informative unless
the narrator offers specific failure
analysis data . . . almost NEVER a
component of such stories.





Bob . . .


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PostPosted: Thu Mar 21, 2019 7:37 am    Post subject: Battery BMS failures? Reply with quote

Quote:

Indeed, the deHavilland DHC-8-202 that I flew in a previous life was fitted with battery temperature gauges on the overhead panel (just below the left fire t-handle in the linked image).

https://bitly.com/2uj9V9F+

The airline I worked for operated them in the desert southwest, where ambient temps routinely exceed 100°F. Given the short-hop, quick-turn nature of the flying we did, and the eye-watering current required to start a >2,000shp engine, we kept a close eye on those gauges.

Eric

Did you ever have occasion to take
a hot battery off line?



Bob . . .


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Eric Page



Joined: 15 Feb 2017
Posts: 116

PostPosted: Thu Mar 21, 2019 8:52 am    Post subject: Battery BMS failures? Reply with quote

Quote:
On Mar 21, 2019, at 08:36, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:

Did you ever have occasion to take a hot battery off line?

Just once, but not in flight. After flying three Phoenix-Yuma-Phoenix round trips on an especially brutal July day, we exceeded limits and couldn’t start up for the fourth scheduled Yuma turn. I can’t say that either of us was particularly bothered by the forced break!

Eric


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PostPosted: Thu Mar 21, 2019 9:30 am    Post subject: Battery BMS failures? Reply with quote

On 21/03/2019 11:36 AM, Robert L. Nuckolls, III wrote:
Quote:
>
> Indeed, the deHavilland DHC-8-202 that I flew in a previous life was
> fitted with battery temperature gauges on the overhead panel (just
> below the left fire t-handle in the linked image).
>
> https://bitly.com/2uj9V9F <https://bitly.com/2uj9V9F>+
>
> The airline I worked for operated them in the desert southwest, where
> ambient temps routinely exceed 100°F. Given the short-hop,
> quick-turn nature of the flying we did, and the eye-watering current
> required to start a >2,000shp engine, we kept a close eye on those
> gauges.
>
> Eric

Did you ever have occasion to take
a hot battery off line?
Bob . . .

An aircraft of that size and vintage may have had a battery charger that

monitored temperature and could limit charging current??
It seems like the Lithium "BMS" strategies are moving in that direction.

Limiting the alternator size as per Earth-X recommendations is a small
step in that direction which I applaud. Even with VRLA batteries I
tossed my 100+ amp alternator in favor of a 40 amp unit.
Ken


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Eric Page



Joined: 15 Feb 2017
Posts: 116

PostPosted: Thu Mar 21, 2019 3:58 pm    Post subject: Battery BMS failures? Reply with quote

Quote:
On Mar 21, 2019, at 10:28, C&K <yellowduckduo(at)gmail.com> wrote:
An aircraft of that size and vintage may have had a battery charger that monitored temperature and could limit charging current??

Don’t quote me on this (it’s been awhile...) but as I recall, the temperature monitoring was separate from the charger. I think the charger’s only “data inputs” were weight-on-wheels and where its AC Power was coming from (external or engine-driven generator).

Eric


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PostPosted: Thu Mar 21, 2019 10:13 pm    Post subject: Battery BMS failures? Reply with quote

I was a 28 year Army Active Duty helicopter pilot. In the mid 70's I had a
Nicad helicopter battery completely melt down. Just molton liquid in the
steel box container. Fortunately the hydrogen did not ignite. We smelled
it and then noticed a terrifically high charge rate. We landed the CH-47
helicopter and we opened the battery box to find the mess. A few years
later the Army put a warning in the manual to land if you smelled the rotten
egg smell and get out of the helicopter get away from it and not to touch
the battery. Finally in the 90s the manufacturer put a battery charger in
the circuit which limited the charge current to about 10 amps. It
prevented thermal runaway charging which could happen with the battery just
tied to the main bus and a 200 amp generator attached to the bus.

--


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PostPosted: Fri Mar 22, 2019 5:53 am    Post subject: Battery BMS failures? Reply with quote

Quote:
An aircraft of that size and vintage may have had a battery charger that monitored temperature and could limit charging current??
It seems like the Lithium "BMS" strategies are moving in that direction.

Don't think so. The 'charger' was not much
different than what we have in our airplanes:
An engine driven power source regulated to
idealized charging levels for the battery.
Some airplanes had two engine driven sources
like starter generators. These would parallel
for delivering up to 800A. The larger
aircraft would also have a auxiliary power
unit good for perhaps 200-300 amps that could
be operated in parallel with ships generators.

None of the generator controls were fitted with
any way to monitor either battery temperature or
current.

Quote:
Limiting the alternator size as per Earth-X recommendations is a small step in that direction which I applaud. Even with VRLA batteries I tossed my 100+ amp alternator in favor of a 40 amp unit.

But suppose your running loads call for more
current? Heated seats maybe? Electric cockpit
heat a la LongEz? A B400 has electric
de=ice on the tail feathers . . . lots
of amps needed there.

Virtually every rechargeable battery's maintenance
instructions call for constant-current/constant-voltage
recharge profiles. I.e. limit current into the
battery to some friendly level until the desired
bus-voltage set point is reached whereupon you
change to constant voltage operation.

All it takes is a current sensor on the battery
feeder to monitor the battery's recharge
current and adjust bus voltage to maintain
fast recharge at the recommended current
until the battery is topped off whereupon
the controller reverts to constant voltage.

Not difficult to do for any combination of
battery and engine driven power sources.


Bob . . .


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PostPosted: Fri Mar 22, 2019 6:01 am    Post subject: Battery BMS failures? Reply with quote

Quote:
Don't quote me on this (it's been awhile...) but as I recall, the temperature monitoring was separate from the charger. I think the charger's only data inputs” were weight-on-wheels and where its AC Power was coming from (external or engine-driven generator).

If the aircraft had 3-phase alternators
and separate starters, then DC power was
derived from transformer/rectifiers to
run DC systems and recharge batteries.

These aircraft were generally large enough
to carry an APU which was used to start
engines thus reducing demands on the battery.

These systems could easily include features
for battery management.

But for twin-jets up through ships like
the Hawker 800 series, batteries were
connected to a bus powered by generators
with a LOT of output capability. Any
necessary monitoring of battery temperatures
was a simple thermometer gage with warning
and danger lights.

It was up to crew to notice and then
take an overheated battery off line until
it cooled.


Bob . . .


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PostPosted: Fri Mar 22, 2019 7:42 am    Post subject: Battery BMS failures? Reply with quote

Quote:
On Mar 22, 2019, at 07:00, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:
If the aircraft had 3-phase alternators and separate starters, then DC power was derived from transformer/rectifiers to run DC systems and recharge batteries.

These aircraft were generally large enough to carry an APU which was used to start engines thus reducing demands on the battery.

The Dash-8s of this vintage had Pratt & Whitney PW123Ds (2,150 shp/side) with starter/generators. There were also AC generators (that’s what they called them!) and TRUs. It was a complex electrical system, to put it mildly.

The planes were available with APUs, but the airline chose not to install them. The reasons for that remained a mystery to most of us who flew them, as the plane was an overpowered beast that had no trouble hauling a full cabin and bulked-out cargo bins. The extra couple hundred pounds would have made zero difference in performance, but would have improved interior comfort and reduced battery demands enormously. As it was, all of our engine starts were battery powered for #2, then tie the DC buses to start #1 assisted by the #2 generator.

Eric


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