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nuckolls.bob(at)aeroelect
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 Posted: Sun Nov 02, 2014 12:22 pm Post subject: lithium facts |
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I've been working on a series of articles for Kitplanes
on the use of lithium batteries in airplanes. Energetic
concerns for making the switch are centered on the extra-
ordinary ability of lithium batteries to catch fire . . .
and set other things on fire too. But then, we went through
similar gyrations of risk assessment and design goals with
the NiCad batteries wwwaaayyyy back when too.
I've been 'playing' with some exemplar cells on the bench
and putting some pretty good miles on my battery-runner-downer-
machine. An interesting feature of this chemistry has bubbled
to the top of my attention. While the Lead-Acid cell chemistry
'tops off' at about 2.4 volts per cell, the lithium cells top
off at 4.2 volts.
Hmmmm . . . so if your electrical system is already designed
around a six-cell lead-acid storage medium with regulator
set to accommodate a 14.4v for topping off lead-acid, how many
cells should the Li-Ion replacement feature . . . and what
changes, if any, should be made to the regulation set-point?
A 3-cell lithium battery gets fully stuffed at 12.6 volts,
a 4-cell array would like to see 16.8 volts. Hmmmm . . .
what's the elegant design goal? We've read in the journals
that the hybrid car guys design their charge-discharge
profiles to operate state-of-charge over a range of 20-80%
to maximize the battery's service life. What happens if
we charge a 4-cell array at 14.4/4 or only 3.6 volts per
cell?
Turns out, this top-off voltage will take a lithium cell to
about 50% of potential capacity of the chemistry. Obviously,
adjusting the regulator on your airplane to 16.0 volts or
more has some serious implications for the rest of the ship's
electro-whizzies. Okay, perhaps we're dollars/weight ahead
by operating a 4-cell array in an un-modified lead-acid system.
That makes for good service life, right?
Maybe, NOW we're talking about 0% to 50% cycle limits on
the lithium product . . . we know that lithium really detests
over-discharge events. How does 0->50 compare with 20->80
favored by the guys who use lithium in cars? Dunno . . . yet.
Don't want speak out of ignorance or get out in front of
the article's completion . . . but it's becoming somewhat
obvious that the 'lead-acid equivalency' cited by marketers
of lithium is less than forthcoming. Yeah, lithium
has 3x the energy density of lead-acid when topped-off. But
if the lead-acid set point charges the battery to only 50%, you
just tossed off the top half of the battery's energy storage
potential.
The upside of this fact suggests that there is no way
that a lithium battery is going to be 'abused' by an
alternator set for 14.4 volts. If an installed lithium
battery goes into energetic self destruction it will have
to be triggered by some stress other than voltage; high-rate
discharge or design/manufacturing failure internal to a cell.
Something to ponder guys . . . watch this space . . .
Bob . . .
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ashleysc(at)broadstripe.n
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| Posted: Sun Nov 02, 2014 1:57 pm Post subject: lithium facts |
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Hi Bob;
I have heard, but have no personal experience, that the danger of fires from lithium iron batteries is much reduced in comparison to lithium ion batteries, while their weight is only slightly greater. So one of my questions is: With which type of battery are you experimenting? If it's not lithium iron, I suggest you get one of those too. My second point is: Could a simple solid state DC voltage regulator be designed to bring the 16.8 V. down to 14.4 V.? This would maximize the potential of the lithium battery.  I have read the AeroElectric Connection through a second time and really appreciate the work you do.
Cheers!  Stu.
On Sun, Nov 2, 2014 at 12:21 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
[quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
I've been working on a series of articles for Kitplanes
on the use of lithium batteries in airplanes. Energetic
concerns for making the switch are centered on the extra-
ordinary ability of lithium batteries to catch fire . . .
and set other things on fire too. But then, we went through
similar gyrations of risk assessment and design goals with
the NiCad batteries wwwaaayyyy back when too.
I've been 'playing' with some exemplar cells on the bench
and putting some pretty good miles on my battery-runner-downer-
machine. An interesting feature of this chemistry has bubbled
to the top of my attention. While the Lead-Acid cell chemistry
'tops off' at about 2.4 volts per cell, the lithium cells top
off at 4.2 volts.
Hmmmm . . . so if your electrical system is already designed
around a six-cell lead-acid storage medium with regulator
set to accommodate a 14.4v for topping off lead-acid, how many
cells should the Li-Ion replacement feature . . . and what
changes, if any, should be made to the regulation set-point?
A 3-cell lithium battery gets fully stuffed at 12.6 volts,
a 4-cell array would like to see 16.8 volts. Hmmmm . . .
what's the elegant design goal? We've read in the journals
that the hybrid car guys design their charge-discharge
profiles to operate state-of-charge over a range of 20-80%
to maximize the battery's service life. What happens if
we charge a 4-cell array at 14.4/4 or only 3.6 volts per
cell?
Turns out, this top-off voltage will take a lithium cell to
about 50% of potential capacity of the chemistry. Obviously,
adjusting the regulator on your airplane to 16.0 volts or
more has some serious implications for the rest of the ship's
electro-whizzies. Okay, perhaps we're dollars/weight ahead
by operating a 4-cell array in an un-modified lead-acid system.
That makes for good service life, right?
Maybe, NOW we're talking about 0% to 50% cycle limits on
the lithium product . . . we know that lithium really detests
over-discharge events. How does 0->50 compare with 20->80
favored by the guys who use lithium in cars? Dunno . . . yet.
Don't want speak out of ignorance or get out in front of
the article's completion . . . but it's becoming somewhat
obvious that the 'lead-acid equivalency' cited by marketers
of lithium is less than forthcoming. Yeah, lithium
has 3x the energy density of lead-acid when topped-off. But
if the lead-acid set point charges the battery to only 50%, you
just tossed off the top half of the battery's energy storage
potential.
The upside of this fact suggests that there is no way
that a lithium battery is going to be 'abused' by an
alternator set for 14.4 volts. If an installed lithium
battery goes into energetic self destruction it will have
to be triggered by some stress other than voltage; high-rate
discharge or design/manufacturing failure internal to a cell.
Something to ponder guys . . . watch this space . . .
 Bob . . .
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fvalarm(at)rapidnet.net
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nuckolls.bob(at)aeroelect
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| Posted: Sun Nov 02, 2014 3:13 pm Post subject: lithium facts |
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At 15:55 2014-11-02, you wrote:
Hi Bob;
I have heard, but have no personal experience, that the danger of fires from lithium iron batteries is much reduced in comparison to lithium ion batteries, while their weight is only slightly greater.
To be sure, there are big differences in how the various
chemistries behave AFTER the fire starts . . . but all
battery chemistries from lead-acid to ni-cad, to lithium
store a lot of energy in a relatively small volume. So
all chemistries present some hazard for rapid release of that
energy to varying degrees. Even the out-gassing products
of Li-Iron are combustible. This is why the True Blue batteries
[/b]  [/b] . . .
have those little 'smoke stacks' on top. They connect to a
vent tube designed to take the nasties over-board in the event
of catastrophic failure within a case DESIGNED to contain
such events.
To test the integrity of the case, the protective features
of the battery management system (BMS) are disabled and
the test lab puts 42 volts to the array of cells. After
a period of time, a 'fog' of nasties begins to pour from
the vent but case temperatures remain quite nominal . . .
non-hazardous to children and other living things aboard
the airplane.
The design philosophy calls for getting this electronic version
of nitro-glycerine packaged in a manner that contains
worst-case failures . . . Damn I love FMEAs! Fooey on that
reliability study stuff . . . assume the worst and tame it.
So one of my questions is: With which type of battery are you experimenting? If it's not lithium iron, I suggest you get one of those too.
These are lithium-iron . . .
http://tinyurl.com/m4mlvsq
but for the purposes of my articles, it doesn't matter. If
the cells being offered by the various vendors take FMEA
into account and drive risks to acceptably low levels,
we have to assume that the energies contained are (1)
only allowed to get out through the terminals as electron
flow or (2) are very low risk due to management of manufacturing
quality and/or some manner of de-rating . . . like operating
them in the lower half of their energy storage tank?
[/b]My second point is: Could a simple solid state DC voltage regulator be designed to bring the 16.8 V. down to 14.4 V? This would maximize the potential of the lithium battery.
This is exactly what the makers of computers, tablets,
cell phones, and other products do. They use chargers
designed for the battery voltage selected . . . and discharge
to switch-mode power supplies that offers the desired system
voltage. Unfortunately, our 'charger' is that belt driven
thingy up front that is not especially tailored to the
care and feeding of lithium. Even if it were, then yes, we'd
need some mater of dc/dc converter to re-flavor the volts
to 14.4.
The thrust of my articles is to explore the cost/benefit
ratio for 'going lithium'. After you've spent the dollars
for the premium product, can you get off shorter runways,
fly over taller mountains, endure longer with a failed
alternator, or carry more baggage?
The design decisions are sort like those we should have
considered when we put those headers and 4-bbl carburetors on
our school transportation car . . . when we were so strapped
for cash that the used tire store was more likely to get
our business than Firestone. Good decision making is called
spontaneous organization, the science of elegant trade-offs.
[/b]I have read the AeroElectric Connection through a second time and really appreciate the work you do.
Cheers!
Thank you for that endorsement. I'm pleased that you find
the work useful.
[/b]
Bob . . . [quote][b]
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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Sun Nov 02, 2014 4:08 pm Post subject: lithium facts |
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Bob,
It seems to me that your question "can you get off shorter runways, fly over taller mountains, endure longer with a failed alternator, or carry more baggage?" adds little to the discussion. I say this because making an airplane light is accomplished by many decisions to save small amounts of weight by going with option B rather than option A, option D rather than option C, etc. The cumulative result of all of these decisions does indeed allow one to get off quicker, climb faster, carry more baggage, etc. However, if we were to evaluate each decision individually, as you seek to do with lithium batteries, probably none of them achieve a meaningful difference in aircraft performance.
The question to ask is not what the effect will be on aircraft performance. We already know that. This is no mystery. The question is already answered, because every pound counts just as much as every other pound when it comes to weight related performance whether it be a lighter battery, the choice of titanium over stainless steel for the firewall, or the decision to go on a diet to achieve a smaller beer belly. It seems to me the important questions are "How does the cost of lithium compare to the cost of lead acid?" and "How does the safety of lithium compare to the safety of lead acid?" Those questions are important. Questions of weight related aircraft performance are merely rhetorical.
On Sun, Nov 2, 2014 at 2:11 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
[quote] At 15:55 2014-11-02, you wrote:
Hi Bob;
I have heard, but have no personal experience, that the danger of fires from lithium iron batteries is much reduced in comparison to lithium ion batteries, while their weight is only slightly greater.
To be sure, there are big differences in how the various
chemistries behave AFTER the fire starts . . . but all
battery chemistries from lead-acid to ni-cad, to lithium
store a lot of energy in a relatively small volume. So
all chemistries present some hazard for rapid release of that
energy to varying degrees. Even the out-gassing products
of Li-Iron are combustible. This is why the True Blue batteries
 . . .
have those little 'smoke stacks' on top. They connect to a
vent tube designed to take the nasties over-board in the event
of catastrophic failure within a case DESIGNED to contain
such events.
To test the integrity of the case, the protective features
of the battery management system (BMS) are disabled and
the test lab puts 42 volts to the array of cells. After
a period of time, a 'fog' of nasties begins to pour from
the vent but case temperatures remain quite nominal . . .
non-hazardous to children and other living things aboard
the airplane.
The design philosophy calls for getting this electronic version
of nitro-glycerine packaged in a manner that contains
worst-case failures . . . Damn I love FMEAs! Fooey on that
reliability study stuff . . . assume the worst and tame it.
So one of my questions is: With which type of battery are you experimenting? If it's not lithium iron, I suggest you get one of those too.
These are lithium-iron . . .
http://tinyurl.com/m4mlvsq
but for the purposes of my articles, it doesn't matter. If
the cells being offered by the various vendors take FMEA
into account and drive risks to acceptably low levels,
we have to assume that the energies contained are (1)
only allowed to get out through the terminals as electron
flow or (2) are very low risk due to management of manufacturing
quality and/or some manner of de-rating . . . like operating
them in the lower half of their energy storage tank?
My second point is: Could a simple solid state DC voltage regulator be designed to bring the 16.8 V. down to 14.4 V? This would maximize the potential of the lithium battery.
This is exactly what the makers of computers, tablets,
cell phones, and other products do. They use chargers
designed for the battery voltage selected . . . and discharge
to switch-mode power supplies that offers the desired system
voltage. Unfortunately, our 'charger' is that belt driven
thingy up front that is not especially tailored to the
care and feeding of lithium. Even if it were, then yes, we'd
need some mater of dc/dc converter to re-flavor the volts
to 14.4.
The thrust of my articles is to explore the cost/benefit
ratio for 'going lithium'. After you've spent the dollars
for the premium product, can you get off shorter runways,
fly over taller mountains, endure longer with a failed
alternator, or carry more baggage?
The design decisions are sort like those we should have
considered when we put those headers and 4-bbl carburetors on
our school transportation car . . . when we were so strapped
for cash that the used tire store was more likely to get
our business than Firestone. Good decision making is called
spontaneous organization, the science of elegant trade-offs.
I have read the AeroElectric Connection through a second time and really appreciate the work you do.
Cheers!
Thank you for that endorsement. I'm pleased that you find
the work useful.
 Bob . . . | Quote: |
_blank">www.aeroelectric.com
.com" target="_blank">www.buildersbooks.com
="_blank">www.homebuilthelp.com
="_blank">www.mypilotstore.com
ank">www.mrrace.com
_blank">http://www.matronics.com/contribution
ist" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
tp://forums.matronics.com
|
[b]
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rlborger(at)mac.com
Guest
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| Posted: Sun Nov 02, 2014 4:32 pm Post subject: lithium facts |
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Ken,
You missed one question: How does the performance of Li battery technology compare to Pb with respect to maintaining our necessary electronic equipment (aka electro-whizzies) until we can make a safe return to terra firma. That was the area of greatest deficiency I found when doing my brief evaluation.
Blue skies & tailwinds,Bob BorgerEuropa XS Tri, Rotax 914, Airmaster C/S Prop (75 hrs).Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP3705 Lynchburg Dr.Corinth, TX 76208-5331Cel: 817-992-1117rlborger(at)mac.com (rlborger(at)mac.com)
On Nov 2, 2014, at 6:04 PM, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Bob,
It seems to me that your question "can you get off shorter runways, fly over taller mountains, endure longer with a failed alternator, or carry more baggage?" adds little to the discussion. I say this because making an airplane light is accomplished by many decisions to save small amounts of weight by going with option B rather than option A, option D rather than option C, etc. The cumulative result of all of these decisions does indeed allow one to get off quicker, climb faster, carry more baggage, etc. However, if we were to evaluate each decision individually, as you seek to do with lithium batteries, probably none of them achieve a meaningful difference in aircraft performance.
The question to ask is not what the effect will be on aircraft performance. We already know that. This is no mystery. The question is already answered, because every pound counts just as much as every other pound when it comes to weight related performance whether it be a lighter battery, the choice of titanium over stainless steel for the firewall, or the decision to go on a diet to achieve a smaller beer belly. It seems to me the important questions are "How does the cost of lithium compare to the cost of lead acid?" and "How does the safety of lithium compare to the safety of lead acid?" Those questions are important. Questions of weight related aircraft performance are merely rhetorical.
[quote][b]
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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Sun Nov 02, 2014 5:18 pm Post subject: lithium facts |
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Yes, I should have included that. Also I should have included "How does Li compare to Pb with respect to cranking the engine?"
On Sun, Nov 2, 2014 at 3:29 PM, Robert Borger <rlborger(at)mac.com (rlborger(at)mac.com)> wrote:
[quote]Ken,
You missed one question: How does the performance of Li battery technology compare to Pb with respect to maintaining our necessary electronic equipment (aka electro-whizzies) until we can make a safe return to terra firma. That was the area of greatest deficiency I found when doing my brief evaluation.
Blue skies & tailwinds,
Bob Borger
Europa XS Tri, Rotax 914, Airmaster C/S Prop (75 hrs).
Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP
3705 Lynchburg Dr.
Corinth, TX Â 76208-5331
Cel: [url=tel:817-992-1117]817-992-1117[/url]
rlborger(at)mac.com (rlborger(at)mac.com)
On Nov 2, 2014, at 6:04 PM, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Bob,
It seems to me that your question "can you get off shorter runways, fly over taller mountains, endure longer with a failed alternator, or carry more baggage?" adds little to the discussion. I say this because making an airplane light is accomplished by many decisions to save small amounts of weight by going with option B rather than option A, option D rather than option C, etc. The cumulative result of all of these decisions does indeed allow one to get off quicker, climb faster, carry more baggage, etc. However, if we were to evaluate each decision individually, as you seek to do with lithium batteries, probably none of them achieve a meaningful difference in aircraft performance.
The question to ask is not what the effect will be on aircraft performance. We already know that. This is no mystery. The question is already answered, because every pound counts just as much as every other pound when it comes to weight related performance whether it be a lighter battery, the choice of titanium over stainless steel for the firewall, or the decision to go on a diet to achieve a smaller beer belly. It seems to me the important questions are "How does the cost of lithium compare to the cost of lead acid?" and "How does the safety of lithium compare to the safety of lead acid?" Those questions are important. Questions of weight related aircraft performance are merely rhetorical.
| Quote: |
_blank">www.aeroelectric.com
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="_blank">www.mypilotstore.com
ank">www.mrrace.com
_blank">http://www.matronics.com/contribution
ist" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
tp://forums.matronics.com
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henador_titzoff(at)yahoo.
Guest
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| Posted: Mon Nov 03, 2014 4:44 am Post subject: lithium facts |
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| Quote: |
On Sun, Nov 2, 2014 at 2:11 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote: | Quote: | My second point is: Could a simple solid state DC voltage regulator be designed to bring the 16.8 V. down to 14.4 V? This would maximize the potential of the lithium battery.
Bob, if a regulator were designed to bring the voltage down to 14.4V, it
would have to deal with the primary purpose of the battery - to start the
engine. That's a lot of amps, making the design more difficult, expensive
and of course, adding more weight.. It is also one more system to
maintain and possibly fail in flight.
--Henador This is exactly what the makers of computers, tablets, cell phones, and other products do. They use chargers designed for the battery voltage selected . . . and discharge to switch-mode power supplies that offers the desired system voltage. Unfortunately, our 'charger' is that belt driven thingy up front that is not especially tailored to the care and feeding of lithium. Even if it were, then yes, we'd need some mater of dc/dc converter to re-flavor the volts to 14.4.
Bob, tablets and smartphones have two advantages in this
regard. First, they are neatly packaged and designed to
work with a single design per device. This means that the
designers maximize all parameters to prevent EMI, and
EMS and power utlization.
Second, once the design is "thoroughly" tested, they make
gazillions of the same thing. Our experimental airplanes are
one of a kind, which means each one is a different design,
electrical-wise. We don't have good control of EMI, EMS
and power utilization across our experimental fleets as it is.
And of course, it will add weight, more maintenance and
decrease system reliability.
--Henador
|
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[quote] | Quote: | The thrust of my articles is to explore the cost/benefit ratio for 'going lithium'. After you've spent the dollars for the premium product, can you get off shorter runways, fly over taller mountains, endure longer with a failed alternator, or carry more baggage?
Bob, you might be able to, because your wallet will weigh
less.
--Henador
|
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nuckolls.bob(at)aeroelect
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| Posted: Mon Nov 03, 2014 10:33 am Post subject: lithium facts |
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At 18:29 2014-11-02, you wrote:
| Quote: | Ken,
You missed one question: How does the
performance of Li battery technology compare to
Pb with respect to maintaining our necessary
electronic equipment (aka electro-whizzies)
until we can make a safe return to terra
firma. That was the area of greatest deficiency
I found when doing my brief evaluation.
|
The present studies are focused on understanding
the capabilities and limits of the lithium technologies
and systems integration issues to be resolved.
There is no answer to your question based purely
on chemistry or application. I was asked by a
supplier of lithium products to help them craft
an application chart . . . a table of various
OBAM aircraft/engines with boxes citing the
recommended lithium product.
I'm not sure they really understood my reluctance
to participate in such an adventure. My advice to
them was simple. Tell the customer EVERYTHING they
need to know to integrate the technology into their
project and how to SIZE it to the task as defined
by that customer's design goals.
I took them to task for that "lead-acid equivalency"
bull-hocky with a suggestion that they were hanging
their fanny way out in the breeze for a lawsuit.
The widow of some pilot downed in the mountains might
have a foundation in PHYSICS to hypothesize that
"Your recommendation of lithium product Z to replace
my husband's lead-acid product X was the proximate
cause of his panel going dark 30 minutes sooner than
if he had NOT followed your recommendation."
At the same time, the OBAM aviation community has both
opportunity and encouragement to gather ALL the
details necessary to make the change-out . . . based
on personal design goals . . . not some poorly
crafted substitution chart offered by the manufacturer.
Patience my friend. We're learning more every day
but data upon which your question depends is not
yet in hand.
At 18:04 2014-11-02, you wrote:
Bob,
It seems to me that your question "can you get
off shorter runways, fly over taller mountains,
endure longer with a failed alternator, or carry
more baggage?" adds little to the discussion. I
say this because making an airplane light is
accomplished by many decisions to save small
amounts of weight by going with option B rather
than option A, option D rather than option C,
etc. The cumulative result of all of these
decisions does indeed allow one to get off
quicker, climb faster, carry more baggage, etc.
However, if we were to evaluate each decision
individually, as you seek to do with lithium
batteries, probably none of them achieve a
meaningful difference in aircraft performance.
The question to ask is not what the effect will
be on aircraft performance. We already know that.
This is no mystery. The question is already
answered, because every pound counts just as much
as every other pound when it comes to weight
related performance whether it be a lighter
battery, the choice of titanium over stainless
steel for the firewall, or the decision to go on
a diet to achieve a smaller beer belly. It seems
to me the important questions are "How does the
cost of lithium compare to the cost of lead
acid?" and "How does the safety of lithium
compare to the safety of lead acid?" Those
questions are important. Questions of weight
related aircraft performance are merely rhetorical.
No argument there. But for all of lithium's uber-hyped
features, WEIGHT is the big-bear in the woods. Okay,
sit down an make a list of ALL opportunities to reduce
aircraft empty weight in order of their probability
of implementation and costs. Hmm . . . carbon fiber
RV-7?. Aluminum IO-360? Smaller tires? Leave off the
brakes? Yeah, the list is silly . . . but I use it
to emphasize the fact that our airplanes are NOT clean
piece of paper designs where weight savings reighns
supreme over perhaps strength, handling qualities,
payload, cockpit comforts, etc. etc. I'm recalling
Voyager here . . . an airplane that needed 5 pounds of
fuel to carry 1 pound of airplane around the world.
Uncle Burt took the task so seriously that he installed
B&C regulators without their housings . . . the electronics
mounted to covers were stood up on spacers. Saved
a few ounces.
THAT approach to 1000 weight savings decisions go
directly toward success or failure of the mission.
But back in the RV builder's shop. Just how many
opportunities REALLY exist for reduction of weight?
The battery as a real chunk of lead/plastic is
an obvious candidate . . . so what size lithium
battery will DO EVERYTHING the existing lead-acid
battery is expected to do?
I am in the early stages of discovery that the
lithium product dropped into a lead-acid optimized
system is physically prevented from exploiting
the full capabilities of the contained chemistry. This
means that a direct lithium replacement might have to
be $TWICE$ as large as originally thought just to
store and deliver the same energy.
OUR discussions/investigations are not conducted
for the benefit of those who use a battery only
for engine cranking. I am operating under the
design goal of finding out exactly how many pounds
and cubic inches of lithium are required to make
a 1:1 change out.
Early discoveries suggest that the real numbers
for weight savings and costs are not nearly so
attractive as the ads would like us to believe.
All creative ventures from cooking to building
airplanes to crafting a good house paint call
for a knowledge of properties of materials and
management of energy.
Until we know those properties and how they
influence our energy management, the answer
is unclear. Finally, there are so few real
opportunities to reduce weight beyond selection
of bolt-on parts. So I'll suggest that the
prudent owner/operator's costs for making
the switch has little opportunity to make
observable improvements in aircraft performance.
Suggest you catch up on the lithium discussions
thus far with a review of first three articles
in Kitplanes and discussions here on the List
over the last year.
Bob . . .
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ceengland7(at)gmail.com
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| Posted: Mon Nov 03, 2014 1:48 pm Post subject: lithium facts |
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This sounds like 'a failure to communicate.'
There would be no electrical performance advantage to Lithium (either will crank the engine), and there could (likely) be a disadvantage (in endurance). So for me, it really boils down to whether the weight savings is worth the pounds saved, and whether the pounds saved is worth the likely reduction in endurance and the unknown increase in risk due to failure (fire).
Now if I could add a second alternator with its controls (for unlimited endurance) and combined with the lithium starting battery, weigh the same or less than single alternator & lead-acid battery, that would begin to tip the scales toward lithium. But the the money and safety questions remain to be resolved.
Charlie
On 11/2/2014 6:04 PM, Ken Ryan wrote:
[quote] Bob,
It seems to me that your question "can you get off shorter runways, fly over taller mountains, endure longer with a failed alternator, or carry more baggage?" adds little to the discussion. I say this because making an airplane light is accomplished by many decisions to save small amounts of weight by going with option B rather than option A, option D rather than option C, etc. The cumulative result of all of these decisions does indeed allow one to get off quicker, climb faster, carry more baggage, etc. However, if we were to evaluate each decision individually, as you seek to do with lithium batteries, probably none of them achieve a meaningful difference in aircraft performance.
The question to ask is not what the effect will be on aircraft performance. We already know that. This is no mystery. The question is already answered, because every pound counts just as much as every other pound when it comes to weight related performance whether it be a lighter battery, the choice of titanium over stainless steel for the firewall, or the decision to go on a diet to achieve a smaller beer belly. It seems to me the important questions are "How does the cost of lithium compare to the cost of lead acid?" and "How does the safety of lithium compare to the safety of lead acid?" Those questions are important. Questions of weight related aircraft performance are merely rhetorical.
On Sun, Nov 2, 2014 at 2:11 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 15:55 2014-11-02, you wrote:
Hi Bob;
I have heard, but have no personal experience, that the danger of fires from lithium iron batteries is much reduced in comparison to lithium ion batteries, while their weight is only slightly greater.
To be sure, there are big differences in how the various
chemistries behave AFTER the fire starts . . . but all
battery chemistries from lead-acid to ni-cad, to lithium
store a lot of energy in a relatively small volume. So
all chemistries present some hazard for rapid release of that
energy to varying degrees. Even the out-gassing products
of Li-Iron are combustible. This is why the True Blue batteries
 . . .
have those little 'smoke stacks' on top. They connect to a
vent tube designed to take the nasties over-board in the event
of catastrophic failure within a case DESIGNED to contain
such events.
To test the integrity of the case, the protective features
of the battery management system (BMS) are disabled and
the test lab puts 42 volts to the array of cells. After
a period of time, a 'fog' of nasties begins to pour from
the vent but case temperatures remain quite nominal . . .
non-hazardous to children and other living things aboard
the airplane.
The design philosophy calls for getting this electronic version
of nitro-glycerine packaged in a manner that contains
worst-case failures . . . Damn I love FMEAs! Fooey on that
reliability study stuff . . . assume the worst and tame it.
So one of my questions is: With which type of battery are you experimenting? If it's not lithium iron, I suggest you get one of those too.
These are lithium-iron . . .
http://tinyurl.com/m4mlvsq
but for the purposes of my articles, it doesn't matter. If
the cells being offered by the various vendors take FMEA
into account and drive risks to acceptably low levels,
we have to assume that the energies contained are (1)
only allowed to get out through the terminals as electron
flow or (2) are very low risk due to management of manufacturing
quality and/or some manner of de-rating . . . like operating
them in the lower half of their energy storage tank?
My second point is: Could a simple solid state DC voltage regulator be designed to bring the 16.8 V. down to 14.4 V? This would maximize the potential of the lithium battery.
This is exactly what the makers of computers, tablets,
cell phones, and other products do. They use chargers
designed for the battery voltage selected . . . and discharge
to switch-mode power supplies that offers the desired system
voltage. Unfortunately, our 'charger' is that belt driven
thingy up front that is not especially tailored to the
care and feeding of lithium. Even if it were, then yes, we'd
need some mater of dc/dc converter to re-flavor the volts
to 14.4.
The thrust of my articles is to explore the cost/benefit
ratio for 'going lithium'. After you've spent the dollars
for the premium product, can you get off shorter runways,
fly over taller mountains, endure longer with a failed
alternator, or carry more baggage?
The design decisions are sort like those we should have
considered when we put those headers and 4-bbl carburetors on
our school transportation car . . . when we were so strapped
for cash that the used tire store was more likely to get
our business than Firestone. Good decision making is called
spontaneous organization, the science of elegant trade-offs.
I have read the AeroElectric Connection through a second time and really appreciate the work you do.
Cheers!
Thank you for that endorsement. I'm pleased that you find
the work useful.
 Bob . . .
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[b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Nov 03, 2014 5:30 pm Post subject: lithium facts |
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At 19:15 2014-11-02, you wrote:
| Quote: | | Yes, I should have included that. Also I should have included "How does Li compare to Pb with respect to cranking the engine?" |
There is no reason for any builder to believe that
lithium products are not suited for cranking their
engine -OR- running all desired electro-whizzies
for a duration that meets design goals.
Further, if you have an AGM battery installed that
already meets your performance goals, then a lithium
replacement for that battery will probably be lighter
and occupy less volume.
If your missions are day-vfr only and you have
no battery only endurance requirements, then
you're on pretty solid ground to accept the marketer's
"lead acid equivalency" or "drop in replacement"
assertions at face value. Further, your purchase
will be MUCH lighter and smaller.
I'm presently in possession of one of these
products:
http://tinyurl.com/jwk9wcu
Note that the ad says this is a 'drop in' replacement
for the Yuasa YTX20 series batteries (18 ah at a
10 hour rate), the YTX24 series (21 a.h.) and the
UB12350 (35 a.h.). This statement should raise some
eyebrows. The ETX36 may indeed CRANK like all of these
batteries it purports to replace.
Here's part of the data I've collected off this sample
thus far:
[img]cid:.0[/img]
When loaded to 5Amps, this battery consistently delivers about
140 watt-hours of stored energy for a 2-hour rate of 11.5
ampere-hours. We also see that this battery's charge cycle
is pretty well ended at 12 volts, one full volt higher than
end of charge on an SLVA battery.
Incidentally, the family of curves cited above shows that
out of the box, charged at 13.0 volts, 14.0 volts, and 15.0
volts, the device dumps a consistent energy value. This speaks
well of the battery's internal battery management system.
So how would this battery stack up for battery-only operations
when replacing any one of the devices for which it is sold as
a drop-in replacement?
These data suggest that if your application calls for a KNOWN
level of stored energy the ETX is NOT a drop in replacement
for the products listed . Assuming that this battery, or one of
its cousins, meets your cranking and stored energy requirements,
then how does it stack up for a weight reduction goal at $350
a pop?
Bob . . .
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ashleysc(at)broadstripe.n
Guest
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| Posted: Mon Nov 03, 2014 9:50 pm Post subject: lithium facts |
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Hi Bob;
Thank you for performing a valuable service in testing lithium iron batteries. You have made a good point that a lithium iron battery may be capable of starting the engine, but may fall short in longevity while running the instruments. One point that has not been made in their favor is that substitution of a 3 to 4# battery for a 20 to 30# one may solve a weight and balance problem without needing to move the battery to the tail cone and adding long and heavy cables.
Cheers!  Stu.
On Mon, Nov 3, 2014 at 5:28 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 19:15 2014-11-02, you wrote:
| Quote: | | Yes, I should have included that. Also I should have included "How does Li compare to Pb with respect to cranking the engine?" |
 There is no reason for any builder to believe that
 lithium products are not suited for cranking their
 engine -OR- running all desired electro-whizzies
 for a duration that meets design goals.
 Further, if you have an AGM battery installed that
 already meets your performance goals, then a lithium
 replacement for that battery will probably be lighter
 and occupy less volume.
 If your missions are day-vfr only and you have
 no battery only endurance requirements, then
 you're on pretty solid ground to accept the marketer's
 "lead acid equivalency" or "drop in replacement"
 assertions at face value. Further, your purchase
 will be MUCH lighter and smaller.
 I'm presently in possession of one of these
 products:
http://tinyurl.com/jwk9wcu
 Note that the ad says this is a 'drop in' replacement
 for the Yuasa YTX20 series batteries (18 ah at a
 10 hour rate), the YTX24 series (21 a.h.) and the
 UB12350 (35 a.h.). This statement should raise some
 eyebrows. The ETX36 may indeed CRANK like all of these
 batteries it purports to replace.
 Here's part of the data I've collected off this sample
 thus far:
[img]cid:.0[/img]
 When loaded to 5Amps, this battery consistently delivers about
 140 watt-hours of stored energy for a 2-hour rate of 11.5
 ampere-hours. We also see that this battery's charge cycle
 is pretty well ended at 12 volts, one full volt higher than
 end of charge on an SLVA battery.
 Incidentally, the family of curves cited above shows that
 out of the box, charged at 13.0 volts, 14.0 volts, and 15.0
 volts, the device dumps a consistent energy value. This speaks
 well of the battery's internal battery management system.
 So how would this battery stack up for battery-only operations
 when replacing any one of the devices for which it is sold as
 a drop-in replacement?
 These data suggest that if your application calls for a KNOWN
 level of stored energy the ETX is NOT a drop in replacement
 for the products listed . Assuming that this battery, or one of
 its cousins, meets your cranking and stored energy requirements,
 then how does it stack up for a weight reduction goal at $350
 a pop?
 Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Tue Nov 04, 2014 7:57 am Post subject: lithium facts |
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To: aeroelectric-list(at)matronics.com
Subject: Re: lithium facts
At 23:49 2014-11-03, you wrote:
Hi Bob;
Thank you for performing a valuable service in testing lithium iron batteries. You have made a good point that a lithium iron battery may be capable of starting the engine, but may fall short in longevity while running the instruments.Â
A conundrum that arises from the inability/
unwillingness of suppliers to offer DATA to
support the customers broader needs.
I've often mentioned the early struggles of
Bolder Technologies to find market niche
for their 1.1 a.h., flashlight-cell sized
jelly-roll products that would crank an
engine but wouldn't run your panel for 10
minutes.
We tested some of those cells at B&C about
15 years ago . . . pretty amazing . . .
when they worked . . . but completely
inappropriate to our mission.
We have a similar situation here. The
energetic hawkers of lithium are quick
to point out engine cranking abilities
in terms of 'equivalencies' but without
hard numbers for EVERY feature of lithium's
performance. So just as we saw with Bolder
products, successful incorporation of
the new technology requires that the
system integrator (that's YOU) understands
the trade offs not only in weight and load
dump but capacity, low temperature performance,
and requirements for exploiting capacity (system
voltage). My early studies have demonstrated
that a 4-cell stack of lithium gets De-rated
in a 14.4v system to approximately 1/2 of
potential capacity.
This means that for cell-paks consisting of
arrays of 26650 cells, the USEFUL capacity
is less than the POTENTIAL capacity. Revisiting
the data published by A123 on their 26650
cell offering we see:
[img]cid:7.1.0.9.0.20141104091241.01fa1008(at)aeroelectric.com.0[/img]
Note that while they speak to a MAX ALLOWABLE charge
voltage of 4.2 (pretty much standard across the spectrum
of lithium cells) they also speak to STANDARD CHARGE
and NOMINAL CAPACITY? with numbers on the same order
as demonstrated by my experiments thus far. A123 data
speaks directly to this 14v system de-rating phenomenon.
One point that has not been made in their favor is that substitution of a 3 to 4# battery for a 20 to 30# one may solve a weight and balance problem without needing to move the battery to the tail cone and adding long and heavy cables.
Very good. Yes, the lighter weight of a lithium
engine cranking battery may indeed offer such
an opportunity . . . as long as all other trade-offs
do not impact system performance in undesirable ways.
I think it improbable that we're going to see really
profound weight ratios. Just as the Bolder cells would
happily dump 400A when new, it was never demonstrated that
they would do that for say 50 times a year for say 4
years in service. We've not yet seen numbers on fielded
products with having a 1:6 weight savings or even
1:4 . . .
Bob . . .
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jan_de_jong(at)casema.nl
Guest
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| Posted: Wed Nov 05, 2014 4:05 am Post subject: lithium facts |
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Bob,
I've been following the LiFePO4 scene for some years and don't quite get
your statement that charging a cell to 3.6V instead of 4.2V would leave
50% of full charge unused.
Maybe that is true for LiFePO4 compared to other lithium products but
not, I believe, for LiFePO4 as such. Maybe that is what you mean?
I believe that the following may be true for a LiFePO4 (A123) cell:
1. there is very little capacity between 3.6V and 4.2V (using a 0.1 or
0.05 C cutoff)
2. the 4.2V maximum is intended for specific fast charging methods with
a short stay at 4.2V followed by a much lower float voltage
3. 4.2V is not immediately damaging but not good for long life
You could test and quantify point 1 above if you like?
Regards,
Jan de Jong
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Wed Nov 05, 2014 8:38 am Post subject: lithium facts |
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At 06:04 2014-11-05, you wrote:
--> AeroElectric-List message posted by: Jan de Jong <jan_de_jong(at)casema.nl>
Bob,
I've been following the LiFePO4 scene for some years and don't quite get your statement that charging a cell to 3.6V instead of 4.2V would leave 50% of full charge unused.
Not 'unused' . . . but not even pumped into the cell during charge for later recovery during discharge . . .
[img]cid:.0[/img][/b]
In the plot above we see the recovered energy plots for the same cell topped off at 3.7 volts and 4.2 volts. When charged at the higher voltage, the cell presents as a 3.7 volt source. When discharged at 5A, the cell tossed in the towel at about 4.4 a.h.
When charged at 3.7 volts, it presents as a 3.4 volt source and tosses in the towel at 2.1 a.h.
Maybe that is true for LiFePO4 compared to other lithium products but not, I believe, for LiFePO4 as such. Maybe that is what you mean?
I have found no literature that speaks to major differences between the lithium couples . . . but in any case, LiFePO4 is the technology of choice.
I believe that the following may be true for a LiFePO4 (A123) cell:
1. there is very little capacity between 3.6V and 4.2V (using a 0.1 or 0.05 C cutoff)
I excerpted an image earlier from A123's specifications for their LiFePO4, 26650 cell where they made it clear that while 4.2 is the max allowable charge voltage, 3.7 was the nominally adopted charge voltage.
2. the 4.2V maximum is intended for specific fast charging methods with a short stay at 4.2V followed by a much lower float voltage
3. 4.2V is not immediately damaging but not good for long life
I've read nothing to date that speaks specifically to such a notion. But anecdotally, the 'big guys' are reported to favor the cycling of lithium in their products between the bounds of 20 and 80 percent of potential charge. Of course, the 'big guys' can PICK their system voltage for the purposes of meeting design goals.
We're pretty much stuck with that belt-driven thingy up front set for 14.4 volts, when divided by 4 yields 3.6 volts. Okay, lets jack up the regulator to 14.8, no big deal.
The point is that properties of materials (LiFePO4) married to our energy management constraints (14.8 volts) says that ANY lithium product we may choose to install will be operated between approx 50% and some lower level close to 0% 0 - assuming that the BMS or pilot watching the battery-only voltage shuts things down at 2.8 x 4 or 11.2 volts.
This idea is re-enforced by the testing I did earlier on an AeroVoltz product which had all the outward appearances of being a 3x4 array of 26650 cells. I suggested before testing that the thing was probably going to test out in the neighborhood of a 7.5 a.h. battery . . . which was confirmed as I recall. I need to dig that data up . ..
You could test and quantify point 1 above if you like?
I think the data gathered and presented above supports my perceptions and subsequent assertions . . . This also lends some understanding for the wide variations in advertised capacity of the various Li products. One supplier may be speaking in practical terms for long life of their product while others may be capitalizing on the chemistry's potential capacity. When used in something with modern power conditioning electronics (constant current to LED in flashlight, switchmode power supply in a computer, etc.) one can indeed stuff more electrons in for future recovery at the higher design point of 4.2 volts. But our 14 volt airplanes and other vehicles are what they are . . . so dropping lithium into the battery box says we're bounded by the 0-50% box which, by the way, promises much longer service life.
Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Wed Nov 05, 2014 9:38 am Post subject: lithium facts |
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Earlier I wrote:
The point is that properties of materials (LiFePO4)
married to our energy management constraints (14.8
volts) says that ANY lithium product we may choose
to install will be operated between approx 50% and
some lower level close to 0% 0 - assuming that the
BMS or pilot watching the battery-only voltage
shuts things down at 2.8 x 4 or 11.2 volts.
This idea needs to be explored further . . .
Q: Okay, just how many times over the lifetime of any given battery in an airplane do we EXPECT to discharge down to zero percent in flight?
A: CLOSE TO ZERO . . . the risks are very low assuming that we've done due diligence with FMEA/architecture, preventative maintenance and Plan-B.
From an operational perspective, all we expect from the battery for 99.9% of all operations is get the engine started. How much energy does that take? Hmmmm . . . 200A x 10 seconds x 12v = 24,000 watt-seconds. How much energy does a 4 x 4 array of 26650 cells charged to 50% of potential capacity contain? About 4 cells wide x 4 cells tall x 3.2 volts x 5A for about 1200 seconds = is about 300,000 watt-seconds, give or take.
So, our 'partially charged' array of cells is only taxed to the tune of about 2% of contained energy once-per-flight-cycle, 50 times a year. After the engine starts, we have DESIGNED the alternator system to assume all loads and recharge the battery.
So what is the projected service-life of the battery when cycled between 50 and 48% of potential charge?
I haven't the foggiest . . . nor does A123 I'll bet. Their engineering data gathering will focus on full-range cycling (like between 2.8 and 4.2 volts per manufacturer's data sheet) or perhaps 20 and 80% per the hybrid car engineer's design goals.
The aviation design goals are unique and a VERY small fraction of the marketplace . . . hence it's unrealistic to expect A123 or anyone else to offer data that goes to meeting our design goals. On the other hand, somebody like Concorde or True Blue is intently interested in meeting aviation-unique design goals.
This is the imperative behind getting our own data set that speaks to meeting OBAM aviation design goals, which may in fact be more expansive than TC design goals. I like to design for battery-only ops for duration of fuel aboard. Beechjet engineers can only dream of such goals.
Bob . . . [quote][b]
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jan_de_jong(at)casema.nl
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| Posted: Wed Nov 05, 2014 9:54 am Post subject: lithium facts |
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millner(at)me.com
Guest
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| Posted: Wed Nov 05, 2014 10:03 am Post subject: lithium facts |
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On 11/5/2014 9:37 AM, Robert L. Nuckolls, III wrote:
| Quote: | 24,000 watt-seconds. How much energy does a 4 x 4 array of 26650 cells charged to 50% of potential capacity contain? About 4 cells wide x 4 cells tall x 3.2 volts x 5A for about 1200 seconds = is about 300,000 watt-seconds, give or take.
So, our 'partially charged' array of cells is only taxed to the tune of about 2% of contained energy once-per-flight-cycle |
Math check! 24/300 = 8%... but 2% is 10's complement, for what that's worth (my mind works that way, at least...)
Paul
[quote][b]
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jay(at)horriblehyde.com
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| Posted: Wed Nov 05, 2014 10:32 am Post subject: lithium facts |
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Hey Paul!
That was a very elegant way of showing the error, in a way that demonstrates how our minds work...
And, I'm loving the arguments presented in the main thread. Thanks to Bob, Matt and all the contributors!
Its the most amazing thing to be able to transcend borders, ideology, theocracy and prejudice as we do here; as is happening in all spheres- and it is changing the world (for the better).
Johannesburg Jay
On 2014-11-05 08:00 PM, Paul Millner wrote:
[quote]
On 11/5/2014 9:37 AM, Robert L. Nuckolls, III wrote:
| Quote: | 24,000 watt-seconds. How much energy does a 4 x 4 array of 26650 cells charged to 50% of potential capacity contain? About 4 cells wide x 4 cells tall x 3.2 volts x 5A for about 1200 seconds = is about 300,000 watt-seconds, give or take.
So, our 'partially charged' array of cells is only taxed to the tune of about 2% of contained energy once-per-flight-cycle |
Math check! 24/300 = 8%... but 2% is 10's complement, for what that's worth (my mind works that way, at least...)
Paul
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jan_de_jong(at)casema.nl
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| Posted: Wed Nov 05, 2014 10:46 am Post subject: lithium facts |
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Well, all I can say - I'm amazed.
I wonder why I never read anything anywhere but 3.6V to 3.7V - with dire
warnings about exceeding much...
By the way, these people show 90% charge at 3.6V (100% at 4.2V):
http://www.powerstream.com/LLLF.htm
Jan de Jong
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