LiFePo4 battery on the firewall?

[scard]

Originally Posted by Low Pass

Kathy,

One thing that might help you is to understand that there is a pretty polarized audience for the LiFePO4 batteries. You either recognize the benefits and accept the risks, or you think they're unacceptably dangerous and will hear nothing of using one. Try asking those who appreciate the benefits and accept the risks for application suggestions. Otherwise, you won't get sincere or productive feedback on your ideas.

Bryan

Just to clarify, our airplane has a LifePO battery on the firewall this very moment and has for the last 200 hours. I've threatened to pull it out many times over many heated technical conversations around the dinner table in our house. It remains currently, but might still be removed soon. The technology has significant issues that even a novice pilot can identify easily. But this conversation is about a "Battery Box" now.

[Bill Boyd]

Originally Posted by NovaBandit

(Cross Posted from the "other" discussion)
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:

https://www.youtube.com/watch?v=8IBapfB0Imo - Full Destruction of a charged cell

https://www.youtube.com/watch?v=TiTqY4FY1yk - Penetration Test 1

https://www.youtube.com/watch?v=XZf2pKzBErk - Penetration Test 2

https://www.youtube.com/watch?v=XymqQ-YlfJ0 - Over Charge


Also, here is some information from Wikipedia, which I know is NOT a infallible source:
http://en.wikipedia.org/wiki/Lithium...battery#Safety

And Finally, from http://www.mpoweruk.com/lithiumS.htm :
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 http://earthxmotorsports.com/wp-cont...l_111017_G.pdf)

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:
http://www.edandcolleen.com/files/RV...htBalance.xlsx
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!)

Ed - aware that you decided in the end to put a Li battery in the factory location, a few questions for you and anyone else wanting to contribute:

To protect occupants and structure in the event of an exotherm event, did you feel the need to enclose or vent it further than simply mounting it behind the baggage bulkhead in the supplied tray?

Are you happy, in practice, with the CG/gross weight trade-off you made by not going for the fullest nose-heavy battery location possible? Does flying with ballast get old? Have you ever actually needed that last bit of forward empty CG to load a bit more in the baggage area and back seats?

Apart from Canada, do the regulators have an issue with approving an aircraft with an empty CG forward of the flight envelope loading limits - i.e. placarded as requiring ballast for solo/min fuel ops?

All questions I'm pondering as I get closer to attaching that final top skin and making tail cone access more "fun."

[Guy Prevost]

I have two EarthX batteries on the firewall of my RV-10. The first is mounted high and has had no issues. The second is mounted lower with only about 10" clearance from the exhaust. That battery did see some heat damage and deformation over about 80 hours of flying. The damage was at the point closest to the exhaust. It performed nominally the entire time. I sent it to EarthX for test and examination, they replaced it even though I admitted that the fault was mine.

I've about 10 hours with the replacement in the same location, but with a reflective radiant heat barrier and some insulation. The radiant barrier is the key and so far, so good. I basically copied my firewall insulation which is the Fiberfrax/SS system suggested by Mr. Horton.

My goal for my (essentially rebuilt) RV-10 was a very light weight and a forward CG for maximum versatility. I have a lightweight Whirlwind prop and the two lightweight batteries on the firewall. I also have two alternators. The parts of my airplane I touch are very nice, the rest of the interior is a textured paint that was done by the original builder and I like quite well. I would do the same again.

I'm just within the forward CG envelope when flying solo, but in general I fly with two 25lb shot bags in the baggage compartment. I can then trim for landing with the rear seats empty. Without the shot bags I can't quite trim it. I can remove the sandbags in 10 seconds for the flights where the cg range and capacity is needed. I've used the capacity when filling the plane with the kids and a week's camping gear. My kids are toddlers now, but they appear to be growing.

It's the best of all worlds in my opinion. I have an amazing, 175+kt IFR plane with an 1100 lb useful load and haven't monkeyed with the engineered gross weight limit.

My steel shot bags are nice looking, compact and easy to handle the few times I have to do so. https://www.sandbagstore.com/fihedusasa25.html

[RickSolana]

The 3 incidents in RVs with EarthX batteries seem to have involved a lot of smoke, but no fire. If that will be the case, which way does the air flow around the bulkhead between the baggage area and the battery location in the tail? If it flows out of the cabin, into the tail, and then out, it seems that takes care of venting. No?

[David Paule]

Kathy, can you tell us how hot an EarthX battery gets if it finally does kick off and out-gas?

I'm building an RV-3B and space between the engine and firewall is very tight. There's plenty of room on the cabin side of the firewall, though, and I can build a box there, either adjacent to the back of the firewall or isolated but near it. The box will be sealed and vented to the exterior.

The answer will guide me: should the box be aluminum or stainless (or titanium)?

Dave

[BillL]

Originally Posted by David Paule

Kathy, can you tell us how hot an EarthX battery gets if it finally does kick off and out-gas?

I'm building an RV-3B and space between the engine and firewall is very tight. There's plenty of room on the cabin side of the firewall, though, and I can build a box there, either adjacent to the back of the firewall or isolated but near it. The box will be sealed and vented to the exterior.

The answer will guide me: should the box be aluminum or stainless (or titanium)?

Dave

Until the official answer comes along, it appears aluminum is good enough based on this graph of exotherm plots.

[EarthX Lithium]

Originally Posted by David Paule

Kathy, can you tell us how hot an EarthX battery gets if it finally does kick off and out-gas?

I'm building an RV-3B and space between the engine and firewall is very tight. There's plenty of room on the cabin side of the firewall, though, and I can build a box there, either adjacent to the back of the firewall or isolated but near it. The box will be sealed and vented to the exterior.

The answer will guide me: should the box be aluminum or stainless (or titanium)?

Dave

Dear Dave,

The highest recorded data while doing the DO-347 testing was 300 degrees Fahrenheit. We are releasing to the public, (we already have an aircraft manufacturer in Europe with this model) the ETX900-VNT model that can be mounted within the cabin as it does have a thermal runaway containment system built in and it can be vented. We should have a press release and detailed information on our website within a week. We have already been taking preorders. The price is $549.

[EarthX Lithium]

Originally Posted by RickSolana

The 3 incidents in RVs with EarthX batteries seem to have involved a lot of smoke, but no fire. If that will be the case, which way does the air flow around the bulkhead between the baggage area and the battery location in the tail? If it flows out of the cabin, into the tail, and then out, it seems that takes care of venting. No?

Dear Rick,

I believe you are referring to the Kitplanes article where it discusses 3 known incidents? If so, one was the RV-8 that is discussed in details on the VAF forum here that did have an aircraft battery in it, the other aircraft was a single person helicopter and the third was a Kitfox homebuilt, both of which were 3 years ago and had the power sport battery models in them. But you are correct, none involved any type of flames.

We are releasing within the next week a new battery model, the ETX900-VNT that does have a built in thermal containment system and it is vented for in cabin installs just as an FYI.

[dmattmul]

I am posting this request and not sure if on the correct forum but thought I would try. I searched the issue and have not found a similar question. VAF probably has the most common since builders on the planet so I thought I would ask. I am running my battery leads through some tight areas and wondered if I had a short to ground (airframe) for some reason what would be the consequences. The airframe I am building is a small single passenger design using a HKS 700 E 4 cycle engine. I am estimating the starter loading at 100 amps? I would like to put a breaker directly on the + side of the battery in case I get a hot to ground short. They make some pretty nice fuses that sit directly on the battery. Has this been done before for an experimental airframe? Thanks

[bobnoffs]

anyone looked into the ''fireproof bags '' used to contain lithium batteries. they are common now at every rc flying field. they come in all sizes and maybe could be adapted as a ''wrap'' instead on a battery box. i asked this question to earth x at osh but they had not.