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Thanks for the followup! Over voltage/over charge is the Achilles heel of the Li batteries.
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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. |
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Eliminating risk isn't the point. Minimizing risk is. |
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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!" |
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 |
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 ;) |
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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. |
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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