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-   -   A very lucky pilot! (LI Iron Battery) (https://vansairforce.net/community/showthread.php?t=120338)

Low Pass 12-09-2014 09:06 AM

Thanks for the followup! Over voltage/over charge is the Achilles heel of the Li batteries.

ColoRv 12-09-2014 09:58 AM

Quote:

Originally Posted by ChiefPilot (Post 939288)
Give that man a dollar!

I completely agree. While some talk about risk analysis, I suspect it's more of a casual term rather than a serious look at the situation. When I replaced the PC-680 with a Shorai LiFePO4 in my -6A a year ago, I was quite content with the risks and mitigations as identified via an FMEA exercise.

I'm curious about the risk analysis you've done. Have you done a test to show how much smoke would enter the cockpit should the battery melt down? Is the plane flyable in that condition? How much of that type of smoke would it take to incapacitate the pilot? What financial protections does your family have should you become incapacitated and plummet into a house or a school?

This discussion and those like it are public and easily found. An attorney fresh out of school will be calling the failure and its consequences easily foreseen...and your build not only liable but negligent.

My job requires daily and constant risk analysis. I've dealt with those attorneys and had to defend my actions. It's less than enjoyable, and I had done everything right with no liability. Defending this battery tech would be significantly more difficult with all of the failures out there. Sure, the FAA allows it under experimental conditions but that does not release you from liability. It places that liability directly on you the manufacturer...and your family....and assets...and future assets.

Sit down and think worst possible scenario versus best possible benefit. Worst....you kill yourself, your neighbors grandson who you offered a ride to and a school bus filled with children. Best possible benefit, you climb an unmeasurable amount faster and your W&B has a slightly smaller number on it. If a battery is significantly affecting your weight and balance or carrying capacity...you've built something wrong.

Low Pass 12-09-2014 10:15 AM

Quote:

Originally Posted by ColoRv (Post 940340)
I'm curious about the risk analysis you've done. Have you done a test to show how much smoke would enter the cockpit should the battery melt down? Is the plane flyable in that condition? How much of that type of smoke would it take to incapacitate the pilot? What financial protections does your family have should you become incapacitated and plummet into a house or a school?

This discussion and those like it are public and easily found. An attorney fresh out of school will be calling the failure and its consequences easily foreseen...and your build not only liable but negligent.

My job requires daily and constant risk analysis. I've dealt with those attorneys and had to defend my actions. It's less than enjoyable, and I had done everything right with no liability. Defending this battery tech would be significantly more difficult with all of the failures out there. Sure, the FAA allows it under experimental conditions but that does not release you from liability. It places that liability directly on you the manufacturer...and your family....and assets...and future assets.

Sit down and think worst possible scenario versus best possible benefit. Worst....you kill yourself, your neighbors grandson who you offered a ride to and a school bus filled with children. Best possible benefit, you climb an unmeasurable amount faster and your W&B has a slightly smaller number on it. If a battery is significantly affecting your weight and balance or carrying capacity...you've built something wrong.

Guess I'm just curious why some here offer so many repeated objections over the Li chemistry battery choice. Thank you! But we get it. There are other considerations using these batteries. The archives will reflect your objections.

SMO 12-09-2014 01:49 PM

Quote:

Originally Posted by ColoRv (Post 940340)
I'm curious about the risk analysis you've done. Have you done a test to show how much smoke would enter the cockpit should the battery melt down? Is the plane flyable in that condition? How much of that type of smoke would it take to incapacitate the pilot? What financial protections does your family have should you become incapacitated and plummet into a house or a school?

This discussion and those like it are public and easily found. An attorney fresh out of school will be calling the failure and its consequences easily foreseen...and your build not only liable but negligent.

My job requires daily and constant risk analysis. I've dealt with those attorneys and had to defend my actions. It's less than enjoyable, and I had done everything right with no liability. Defending this battery tech would be significantly more difficult with all of the failures out there. Sure, the FAA allows it under experimental conditions but that does not release you from liability. It places that liability directly on you the manufacturer...and your family....and assets...and future assets.

Sit down and think worst possible scenario versus best possible benefit. Worst....you kill yourself, your neighbors grandson who you offered a ride to and a school bus filled with children. Best possible benefit, you climb an unmeasurable amount faster and your W&B has a slightly smaller number on it. If a battery is significantly affecting your weight and balance or carrying capacity...you've built something wrong.

Doesn't that argument work just as well just for flying any aircraft regardless of battery choice? Engines fail - there are stats to prove it - so isn't that a foreseeable event that could have the same effect?

krw5927 12-09-2014 02:38 PM

Quote:

Originally Posted by SMO (Post 940388)
Doesn't that argument work just as well just for flying any aircraft regardless of battery choice? Engines fail - there are stats to prove it - so isn't that a foreseeable event that could have the same effect?

Perhaps. But is there a slightly heavier engine that doesn't fail nearly as often, or that, when it does fail, doesn't do so in quite so spectacular a manner? If so, then it may be considered reasonable to choose that one instead.

Eliminating risk isn't the point. Minimizing risk is.

Ironflight 12-09-2014 03:17 PM

Quote:

Originally Posted by krw5927 (Post 940411)
Eliminating risk isn't the point. Minimizing risk is.

Ahhh....but the point is...when have you minimized it ENOUGH? Every person has a different risk line - the line they don't want to cross. Everyone thinks everyone else's risk line is either too conservative, or too liberal. I've played this game professionally my whole life.

When looking at problems like these, you need to look at risk TRADES. I was a firefighter for several decades, and saw a lot of lead/acid battery explosions in vehicles - so they happen as well. It is not a case of zeroing out the risk by not using a Lithium-based battery. There is risk the other way as well.

To quote that (now) old movie..."Interesting game - the only way to win is not to play!"

digidocs 12-09-2014 10:33 PM

If you're going to use a lithium battery in your plane, please get one with a built-in Battery Management System (BMS).
A BMS would have likely prevented this fire by disconnecting the battery cells once the voltage started to run away.

EarthX batteries do have a built-in BMS and others may also.

The Shorai and Aerovoltz do not have a BMS.

Fly safe,
David

Andy Hill 12-10-2014 02:34 AM

Couple of thoughts...

Bad Regulator => Over volts => (non BMS) Li battery = issue (probably).

Firstly, whilst the OP puts down to a poor regulator "and now has a good one", it would seem more important (and not just for the battery, but avionics) is a OV unit (Crowbar?) - which some alternators (e.g. PP) have built in.

Secondly, most of us in RVs have fancy EFIS/EMS systems. Seems there is scope for ensuring there is a red warning / alert / noise at as low a Voltage as you can set in Normal Ops. Then even the first sign of rising voltage gives you a chance to shut off the Alternator.

As Paul says, it's risk assessment and mitigation, the ultimate of which is "don't fly" :eek: There are lots of Li batteries flying, very few incidents, but anything that can be done to "trap" those incidents before they become hazards has to be a benefit ;)

ChiefPilot 12-10-2014 08:38 AM

Quote:

Originally Posted by ColoRv (Post 940340)
I'm curious about the risk analysis you've done. Have you done a test to show how much smoke would enter the cockpit should the battery melt down? Is the plane flyable in that condition? How much of that type of smoke would it take to incapacitate the pilot? What financial protections does your family have should you become incapacitated and plummet into a house or a school?

I did an FMEA exercise through which I identified potential risks and their mitigations. For example, exothermic failure with case venting is a risk that has several mitigations: battery external to cockpit, battery mounted in a location away from fuel/oil lines, and an aural indication of over voltage condition. An example of a less critical failure mode is discharging completely following an alternator failure whilst in IMC conditions - the mitigations for that include aural annunciation of alternator failure, a standby battery for the EFIS, and testing to determine how long the battery can run nav/com equipment sans charging source.

I appreciate your concern for risk management - too often we see examples of TLAR ("that looks about right") engineering that has obvious risks with no mitigations. That said, I find that hyperbole ("plummet into a house or school") to often be a sign of persuasion through fear, not knowledge.

1001001 12-16-2014 08:01 PM

Folks, if you are considering a lithium ion battery of any type in your aircraft or other vehicle, do yourselves a favor and read the recently released NTSB report on the JAL 787 Yuasa battery failure. It includes information related to two other lithium chemistry battery failures on the 787 fleet.

http://www.ntsb.gov/investigations/A...s/AIR1401.aspx

Read the report *fully* and understand its implications. While lithium battery chemistry does not equal certain death and any sort of high density energy storage device can be said to be dangerous, this report details some important points to be aware of.

I won't get into the details of the report, because I feel it is important for experimenters to fully understand for themselves the issues raised. That said, the report deals with several potential root causes they considered, all of which are important to consider and address in a battery installation. One particular detail I will mention is that of wrinkles introduced by the cell manufacturing process in the individual cell windings. These wrinkles possibly resulted in internal short circulating of at least one individual cell in the battery, which led to thermal runaway (exotherm) of that cell, cascading to most of the other cells. Failure modes such as this can be independent of the specific chemistry of the battery.

I make no claims to special knowledge on the topic, and I still am undecided as to whether I would use a lithium cell battery in a project, but I encourage folks to read the report. I certainly learned a lot about battery manufacturing and the details of lithium cells in particular.


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