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EdKranz
Joined: 29 Dec 2010
Posts: 132
Location: Hastings, MN
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 Posted: Thu Aug 07, 2014 10:27 am Post subject: LiFePo4 Battery on the Firewall, Part II |
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(Cross Posted from the "other" discussion)
The feedback to my initial question has been great! Discussions like this are always a good thing!
I've gathered some more data, based on some of the concerns raised in this discussion. The main issues brought up areÂ
1: Safety
2: Performance and capacity
3: Weight and Balance.
Warning! Info dump to follow!
1: Safety
I looked at a few scientific research papers on the safety of LiFePo4 battery cells, and I was actually able to understand some of the words! After uncrossing my eyes, I actually searched something asked for in this discussion; what do these cells do when they are abused. I found some interesting videos:
[url]]https://www.youtube.com/watch?v=8IBapfB0Imo[/url] - Full Destruction of a charged cell
[url]]https://www.youtube.com/watch?v=TiTqY4FY1yk[/url] - Penetration Test 1
[url]]https://www.youtube.com/watch?v=XZf2pKzBErk[/url] - Penetration Test 2
[url]]https://www.youtube.com/watch?v=XymqQ-YlfJ0[/url] - Over Charge
Also, here is some information from Wikipedia, which I know is NOT a infallible source:
[url]]http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery#Safety[/url]
And Finally, from [url]]http://www.mpoweruk.com/lithiumS.htm[/url] :
Phosphate based technology possesses superior thermal and chemical stability which provides better safety characteristics than those of Lithium-ion technology made with other cathode materials. Lithium phosphate cells are incombustible in the event of mishandling during charge or discharge, they are more stable under overcharge or short circuit conditions and they can withstand high temperatures without decomposing. When abuse does occur, the phosphate based cathode material will not burn and is not prone to thermal runaway. Phosphate chemistry also offers a longer cycle life.
Recent developments have produced a range of new environmentally friendly cathode active materials based on Lithiated transition metal phosphates for Lithium-ion applications.
2: Performance and Capacity
Some of the questions brought up relating to this were the operating temperatures that a LiFePo4 battery would encounter on the firewall of an RV10. I had asked the EarthX rep this question at Osh, and his response was this: "The operating range of the EarthX battery is wider than a comparable Odyssey SLA battery". This looks to be mostly true, as the Odyssey manual lists the range without a protective metal case to be only good to 113°F, but 176°F with an added shield. I'd imagine that you could add a similar, or even the same shield to the EarthX to get even more temperature range.Â
Also, a few of our fellow RV10 pilots are going to stick some temperature probes on the firewall in a few places to see what the requirements really are. As it stands today, it doesn't sound like temperature is going to be an issue.
Odyssey Operating Temperature RangeÂ
PC545, PC680, PC925, PC1200 and PC1700 without metal jacket: -40°C (-40°F) to 45°C (113°F),
PC545, PC680, PC925, PC1200 and PC1700 with metal jacket: -40°C (-40°F) to 80°C (176°F),Â
EarthX Operating Temperature Range
Operating Temperature* -30°C (-22°F) to +60 °C (140°F)
Storage Temperature -40°C (-40°F) to +60 °C (140°F)
EarthX Discharge Versus Temperature
We use a similar Cold Cranking Amp test standard (SAE test performed at 0°F, but 3Â
second discharge time) as the lead acid battery manufacturers. As such, our battery with aÂ
similar CCA rating as a lead acid battery should provide the same cranking performanceÂ
at 0°F. But, below 0°F an equivalent lead acid battery will outperform a lithium battery
(From [url]]http://earthxmotorsports.com/wp-content/uploads/2014/01/ETX_Manual_111017_G.pdf[/url])
As far as capacity, the EarthX battery that I am considering has 12ah. According to Skytec's specs, the 149-NL starter that I'm going to use has a draw of 125-185 amps. The 12ah battery will give me almost 4 minutes of solid cranking at the highest spec'd starter draw. As far as electrical emergency capacity, between whatever is left in the starter battery (say after 2 minutes of engine crank) and a 6ah TCW backup battery, I'll have 12ah, which at 6 amps of draw (rough estimate) gives me two hours of endurance buss time. And that is if both the primary and secondary alternators fail.
3: Weight and Balance
Taking the suggestion of a few people in this discussion, we figured out an example weight and balance for a generic RV10, found the arms of the battery tray and the firewall, and ran the numbers with a 26lb battery in the tail, and a 4lb battery on the firewall. Even with the battery on the firewall and 26lbs removed from the tail, it's difficult to get the plane into a CG past the forward limits. Pretty much any weight you carry in the plane pushes the CG back. So, worst case scenario would be a light pilot on low fuel. Even with the stock battery in the stock location, you'll be forward of the CG limit. Adding ~40 lbs in the baggage area will keep the plane within CG in this light configuration, and have the benefit of being removable when carrying capacity is needed. If even a single 65lb person is in the back seat, this extra weight isn't needed.
The real problem is hitting the aft CG before you hit gross weight, because, as I stated before, pretty much every pound you add pushed the CG rearward. Because of this, I personally would prefer to have a CG as far forward as possible to give me more options.
Basically, having the battery in the tail only moves the cg aft 1" in a single pilot no fuel scenario
but allows you to carry 30lbs more baggage in a full gross scenario.
The one thing these numbers don't include are the weight and CG changes from removing the large #2 power cable from the tailcone to the firewall.
Thehe WnB spreadsheet I've used for my numbers is here:
[url]]http://www.edandcolleen.com/files/RV10WeightBalance.xlsx[/url]
Thanks to Justin Twilbeck for throwing this together for me. (It even has a calculation for the loading needed to cause a tailstrike! Good stuff!)
[quote][b]
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_________________
Ed Kranz
RV10
Finishing
www.edandcolleen.com |
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carl.froehlich(at)verizon
Guest
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| Posted: Thu Aug 07, 2014 2:46 pm Post subject: LiFePo4 Battery on the Firewall, Part II |
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Ed,
Nice summary - thanks.
On your amp-hr calculations you will need to factor in the amp-hr capacity assumption. Most amp-hr capacity specifications are at the 10 hour discharge rate. In other words the best circumstances to get the highest number.
This is why we never get the crank time you think doing the simple math. As the discharge rate increases the amp-hr capacity dramatically decreases. So a 10 amp-hr battery will discharge 1 amp per hour for 10 hours. At 10 amps per hour discharge you can assume less than 30 minutes of capacity. At 100 amps per hour figure less than a minute of capacity.
So the best way to figure out what you can expect is to look at the batteries amp-hr capacity versus discharge rate. Once done then double the resulting battery capacity so you can have some margin for a less than fully charged battery or one that's age has degraded from "new battery" spec.
Carl
On Aug 7, 2014, at 2:26 PM, Ed Kranz <ed.kranz(at)gmail.com (ed.kranz(at)gmail.com)> wrote:
[quote](Cross Posted from the "other" discussion)
The feedback to my initial question has been great! Discussions like this are always a good thing!
I've gathered some more data, based on some of the concerns raised in this discussion. The main issues brought up are
1: Safety
2: Performance and capacity
3: Weight and Balance.
Warning! Info dump to follow!
1: Safety
I looked at a few scientific research papers on the safety of LiFePo4 battery cells, and I was actually able to understand some of the words! After uncrossing my eyes, I actually searched something asked for in this discussion; what do these cells do when they are abused. I found some interesting videos:
[url]]https://www.youtube.com/watch?v=8IBapfB0Imo[/url] - Full Destruction of a charged cell
[url]]https://www.youtube.com/watch?v=TiTqY4FY1yk[/url] - Penetration Test 1
[url]]https://www.youtube.com/watch?v=XZf2pKzBErk[/url] - Penetration Test 2
[url]]https://www.youtube.com/watch?v=XymqQ-YlfJ0[/url] - Over Charge
Also, here is some information from Wikipedia, which I know is NOT a infallible source:
[url]]http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery#Safety[/url]
And Finally, from [url]]http://www.mpoweruk.com/lithiumS.htm[/url] :
Phosphate based technology possesses superior thermal and chemical stability which provides better safety characteristics than those of Lithium-ion technology made with other cathode materials. Lithium phosphate cells are incombustible in the event of mishandling during charge or discharge, they are more stable under overcharge or short circuit conditions and they can withstand high temperatures without decomposing. When abuse does occur, the phosphate based cathode material will not burn and is not prone to thermal runaway. Phosphate chemistry also offers a longer cycle life.
Recent developments have produced a range of new environmentally friendly cathode active materials based on Lithiated transition metal phosphates for Lithium-ion applications.
2: Performance and Capacity
Some of the questions brought up relating to this were the operating temperatures that a LiFePo4 battery would encounter on the firewall of an RV10. I had asked the EarthX rep this question at Osh, and his response was this: "The operating range of the EarthX battery is wider than a comparable Odyssey SLA battery". This looks to be mostly true, as the Odyssey manual lists the range without a protective metal case to be only good to 113°F, but 176°F with an added shield. I'd imagine that you could add a similar, or even the same shield to the EarthX to get even more temperature range.
Also, a few of our fellow RV10 pilots are going to stick some temperature probes on the firewall in a few places to see what the requirements really are. As it stands today, it doesn't sound like temperature is going to be an issue.
Odyssey Operating Temperature Range
PC545, PC680, PC925, PC1200 and PC1700 without metal jacket: -40°C (-40°F) to 45°C (113°F),
PC545, PC680, PC925, PC1200 and PC1700 with metal jacket: -40°C (-40°F) to 80°C (176°F),
EarthX Operating Temperature Range
Operating Temperature* -30°C (-22°F) to +60 °C (140°F)
Storage Temperature -40°C (-40°F) to +60 °C (140°F)
EarthX Discharge Versus Temperature
We use a similar Cold Cranking Amp test standard (SAE test performed at 0°F, but 3
second discharge time) as the lead acid battery manufacturers. As such, our battery with a
similar CCA rating as a lead acid battery should provide the same cranking performance
at 0°F. But, below 0°F an equivalent lead acid battery will outperform a lithium battery
(From [url]]http://earthxmotorsports.com/wp-content/uploads/2014/01/ETX_Manual_111017_G.pdf[/url])
As far as capacity, the EarthX battery that I am considering has 12ah. According to Skytec's specs, the 149-NL starter that I'm going to use has a draw of 125-185 amps. The 12ah battery will give me almost 4 minutes of solid cranking at the highest spec'd starter draw. As far as electrical emergency capacity, between whatever is left in the starter battery (say after 2 minutes of engine crank) and a 6ah TCW backup battery, I'll have 12ah, which at 6 amps of draw (rough estimate) gives me two hours of endurance buss time. And that is if both the primary and secondary alternators fail.
3: Weight and Balance
Taking the suggestion of a few people in this discussion, we figured out an example weight and balance for a generic RV10, found the arms of the battery tray and the firewall, and ran the numbers with a 26lb battery in the tail, and a 4lb battery on the firewall. Even with the battery on the firewall and 26lbs removed from the tail, it's difficult to get the plane into a CG past the forward limits. Pretty much any weight you carry in the plane pushes the CG back. So, worst case scenario would be a light pilot on low fuel. Even with the stock battery in the stock location, you'll be forward of the CG limit. Adding ~40 lbs in the baggage area will keep the plane within CG in this light configuration, and have the benefit of being removable when carrying capacity is needed. If even a single 65lb person is in the back seat, this extra weight isn't needed.
The real problem is hitting the aft CG before you hit gross weight, because, as I stated before, pretty much every pound you add pushed the CG rearward. Because of this, I personally would prefer to have a CG as far forward as possible to give me more options.
Basically, having the battery in the tail only moves the cg aft 1" in a single pilot no fuel scenario
but allows you to carry 30lbs more baggage in a full gross scenario.
The one thing these numbers don't include are the weight and CG changes from removing the large #2 power cable from the tailcone to the firewall.
Thehe WnB spreadsheet I've used for my numbers is here:
[url]]http://www.edandcolleen.com/files/RV10WeightBalance.xlsx[/url]
Thanks to Justin Twilbeck for throwing this together for me. (It even has a calculation for the loading needed to cause a tailstrike! Good stuff!)
| Quote: |
D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
List"">http://www.matronics.com/Navigator?RV10-List
D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
//forums.matronics.com
D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
ot;">http://www.matronics.com/contribution
D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
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Lenny Iszak
Joined: 23 Mar 2008
Posts: 270
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| Posted: Fri Aug 08, 2014 6:16 am Post subject: Re: LiFePo4 Battery on the Firewall, Part II |
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Ed,
I have a bunch of truly experimental stuff in my plane. I built a bunch of electronics from scratch, I have a few Arduinos running the show, and I went pretty far trying to build my own EFIS. Just before getting ready to fly I chickened out, admitted defeat, dumped the whole idea and called Rob from AFS  I practically dumped a boatload of money and even more time right out the window, but i'm still very happy with my decision.
You can build pretty complex and cool systems, but when it comes to flying with them the pucker factor sneaks up on you, which you never think of when designing and building these things.
When I started out I always thought that I can build something better than what's on the market. Now I have a lot of respect for these guys because I know how much testing and tweaking is involved to make things work properly and reliably. It almost never works right the first time around.
Yes, you can fly around with a funky new lithium battery by yourself in Phase I, but I want to see you put your family in the plane and not worry about that battery catching on fire.
You can save those 20lbs on your interior instead of the battery. Instead of real cowhide use synthetic leather on your seats. Paint your doors instead of adding funky door panels, use a single stage paint, etc.
Another aspect is that with a 12ah battery you'll be afraid to have your master on for even short periods of time. I know I worry about draining my battery even with my PC925. Once you drain your battery down pretty good the alternator starts charging at close to full power. I know it's designed to do that, but I don't like to see that going on when i'm flying. Besides, it's hard on the regulator, hard on the belt and so on.
I looked at the Shorai batteries very briefly trying to shave off some pounds because my air conditioning adds 50lbs to my empty weight. I did a quick image search to see what form factors they come in and i saw a couple of melted ones. Moved on... I'd rather be flying fat Albert with less junk in the baggage than worrying.
If I built a plane again, I'd use proven reliable parts and not take 6 years building it...
At OSH I got this perseverance award plaque from the EAA. It says: "In recognition of the EAA members who have pursued, with stamina and tenacity, the ultimate fullfillment of building an aircraft no matter how long it took." Anda reads it and she says: Oh cool! Did you get that cause you took so long?
Lenny
PS: Btw, I can get you a pretty good price on Odyssey batteries
| | - The Matronics RV10-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?RV10-List |
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Tim Olson
Joined: 25 Jan 2007
Posts: 2872
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| Posted: Fri Aug 08, 2014 12:11 pm Post subject: LiFePo4 Battery on the Firewall, Part II |
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Well better late than never, I always say, eh Lenny?
You only missed out on a dozen or so cool RV-10 trips.
We'll get you caught up.
The thing that shocked me is, if I was doing that battery,
I really don't think I'd trust that the smaller one would
do it for me up here in North country. I know for sure that
there was someone that switched from 680's to 925's just
for more crank, who lives up north. So if I went with the
EarthX, I'd go for the ETX48E for sure.
Then I looked at the price and see that they sell for $725
or so. That one really floored me!
I don't care if it IS an 8 year battery....unless you can
do a proper load test you can't in good conscience simply
TRUST that it's good at 7 years, or 6 years, or 5 years.
So you'd have to come up with some sort of replacement
timeline. I personally am on my 3rd PC925. They're what,
$135 or so from what I paid last? Even though they're a
5 year battery, I felt it best to cut them off at 3 years.
There's always a secondary use for the batteries. One of
mine is used for charging cellphones at OSH. That battery
is still good from 2005. Another one powers my Tow Buddy
power tug. So I don't even TRY to run them for max life
in the aircraft. My aux batteries I also replace on a 2-3
year schedule. They're just like UPS batteries at work,
and those usually last 2-7 years, depending on abuse.
So if I had an EarthX, and it really is an 8 year battery,
(have they been making them 8 years, to know that the
claim is true?) I personally would cut it off around
4 years, maybe 5 if I pushed it, but 5 is quite a long
time. Even at that point you're talking over $100/year
for just the cost of that one battery.
In 15 years, you'd have $2175 (at today's prices, roughly)
in batteries on a 5 year replacement. With a PC925,
you'd have 5 changes at 3 year replacement, for about $675.
That's over 3x the cost even over 15 years, with what
I'd consider reasonably shortened life expectancies.
Something over 250-270 gallons of avgas. If there's
one thing I've learned about flying the RV-10, it isn't
cheap by any means. Sure, it's more efficient than
flying some slow planes, especial Carbureted where LOP
is tough to do, but it's not super cheap. Insurance
is going to be North of $3000 for any new owner, and
I still figure my hourly operational cost is around
$125/hr altogether. It's enough, anyway, to make
me think twice about putting time on at times.
So weight and balance, fire, space, or any other issues
aside, I just don't see the economics of it. It's
hard enough to afford all the post-flying tools a guy
needs, like Compression testers, bead breakers, and
all sorts of other things you fill your toolbox with,
without adding all that cost too.
Maybe the EarthX 36 sized battery will work, but, if it
doesn't, it's another time and money wasting experiment,
involving new wire pulls and additional downtime. Lenny's
the guy to tell ya, NOT flying is a hell of a lot less
fun than flying. Rework sucks.
Enough on the topic from me though. I'm sure we can
talk about it at OSH 2015 again...
Tim
On 8/8/2014 9:16 AM, Lenny Iszak wrote:
| Quote: |
<lenard(at)rapiddecision.com>
Ed,
I have a bunch of truly experimental stuff in my plane. I built a
bunch of electronics from scratch, I have a few Arduinos running the
show, and I went pretty far trying to build my own EFIS. Just before
getting ready to fly I chickened out, admitted defeat, dumped the
whole idea and called Rob from AFS I practically dumped a boatload
of money and even more time right out the window, but i'm still very
happy with my decision.
You can build pretty complex and cool systems, but when it comes to
flying with them the pucker factor sneaks up on you, which you never
think of when designing and building these things.
When I started out I always thought that I can build something better
than what's on the market. Now I have a lot of respect for these guys
because I know how much testing and tweaking is involved to make
things work properly and reliably. It almost never works right the
first time around.
Yes, you can fly around with a funky new lithium battery by yourself
in Phase I, but I want to see you put your family in the plane and
not worry about that battery catching on fire.
You can save those 20lbs on your interior instead of the battery.
Instead of real cowhide use synthetic leather on your seats. Paint
your doors instead of adding funky door panels, use a single stage
paint, etc.
Another aspect is that with a 12ah battery you'll be afraid to have
your master on for even short periods of time. I know I worry about
draining my battery even with my PC925. Once you drain your battery
down pretty good the alternator starts charging at close to full
power. I know it's designed to do that, but I don't like to see that
going on when i'm flying. Besides, it's hard on the regulator, hard
on the belt and so on.
I looked at the Shorai batteries very briefly trying to shave off
some pounds because my air conditioning adds 50lbs to my empty
weight. I did a quick image search to see what form factors they come
in and i saw a couple of melted ones. Moved on... I'd rather be
flying fat Albert with less junk in the baggage than worrying.
If I built a plane again, I'd use proven reliable parts and not take
6 years building it...
At OSH I got this perseverance award plaque from the EAA. It says:
"In recognition of the EAA members who have pursued, with stamina and
tenacity, the ultimate fullfillment of building an aircraft no matter
how long it took." Anda reads it and she says: Oh cool! Did you get
that cause you took so long?
Lenny
PS: Btw, I can get you a pretty good price on Odyssey batteries
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=428204#428204
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