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Discussion in 'Home Builders and Sport Pilots' started by Let'sgoflying!, Mar 19, 2017.
you should be fine....
Check my Six almost never offers a shred of information. She/he just takes chips at other people's comments. Anyone else notice that? That's the internet.
I have, actually, and I've decided against them partially because I believe their BMS to be less than advertised. The biggest concern I have is that their BMS won't work with some rotax engines because the electrical characteristics are "outside the BMS design specification". Ok, fair enough - but they didn't have an answer for how that is different from a failed Lycoming electical system going haywire (VR failure, etc). I can't and won't say they have a bad product, but I will say that I didn't see the value they were claiming for their BMS.
The mostly likely failure mode producing fireworks would be a failed VR resulting in high voltage being applied to the battery. The risk mitigation here is two fold: a crowbar overvoltage mechanism which will kill the voltage applied to the alternator field almost instantly should it detect an over-voltage condition, visual and aural annunciations if voltage exceeds 14.5v plus an alternator field switch. Should my Shorai battery fail, however, it will do so safely. It's installed on the external side of the firewall, which means no noxious fumes in the cockpit. It's in box away from fuel/oil lines, so the hot gases escaping aren't going to start a fire. And since the Shorai battery was half the price of an earthX, I actually tested one to self destruction by overcharging it in a controlled condition - I know exactly what it's thermal runaway characteristics look like (swelled case, some smoke, no fire - completely unlike a LiPo failure). The crowbar OV protection circuit is advertised to trip in 5ms, although I suspect it's probably more like 200ms or so when the field fuse blow time is taken into account - and that's well under the ~12 minutes that 18V took to induce battery failure.
As a fellow builder, I'm sure you've done similar risk assessment, analysis, design, and test exercises against the EarthX battery as part of your due diligence and determined that it met the level of risk you were willing to undertake.
B&C alternator and regulator. Overvolt protection. Battery status idiot light. I'm about as worried of a battery problem as I am of getting mad cow disease from my burger at lunch. I appreciate your perspective and comments.
Let's just say.....there's a reason that all the Li batteries on the 787 are contained in an armor proof-vented box.
What is a "proof-vented" box?
here's more eye candy....
You missed my point entirely which is the phrase "proof-vented" has no inherent meaning. Perhaps you meant to say a "fire containment box"?
perhaps you are picking nits?
Perhaps you in denial?
Don't take it as criticism. Take it as "we are looking out for you". I too am building my own airplane. The EarthX batteries are NOT immune from the problems we are discussing:
1 failure report from three years ago with no history of how the battery was charged or used. If I can counter that with 20 pireps from guys I know who've used EarthX for those three years which should I favor?
Tell me what you know, not what that one internet story says. How many failures have occurred in your circle of friends? How many successes? How much effort have you put into discovering what causes failures? Do those causes apply to your airplane? See where I'm going with this? In Anchorage we have airplane parts shops like you guys have NAPA. I've spoken with several local dealers. The total failure reports I've heard is one, and that was a failure due to improper charging while parked. As I type this I'm sitting next to my Optimate LFP battery charger so I'm not worried about charging problems.
one in twenty.....or 5% failure rate ain't all that hot....
but, no worries. You should be fine....
Quite frankly one failure is too many in an aviation application, particularly if it's INSIDE the cabin in an unvented situation. It's your plane and your choice, but to sit there and say its perfectly safe technology is completely ignorant and misleading.
Particularly considering your defense of the technology is "my friends say its safe" with no scientific proof to back it up. There's a point where this is looking like denial.
CMS isn't very good at reading, either. One failure among several dealers' total sales. And that failure was explained easily. You guys are fear mongers. I had an engine blow a rod in flight yet I still fly. Using your thinking I should give up aviation. In my thinking I'll just manage the risk. Like I do with literally everything in life.
There's no alternative to an engine, so those risks are assumed and mitigated. There's a safe reliable alternative to Lithium Batteries that we've been using for a hundred years. So if you could reduce risk, why would you not?
Like I said its your choice, I'm just arguing the scientific point of view.
To stay in the scientific mode, its not like lead acid batteries never fail dramatically:
Well, scientifically, lead-acid batteries have exploded before as well and it's a bit more of an exciting event than a LiFEPo4 battery cooking off.
But in any event, I'm not a scientist - I'm an engineer. And that means identifying the risks and designing a solution that tolerates failure should those risks materialize. If my battery cooked off, I could still navigate to an alternate in IMC and shoot an approach without having to breath any noxious fumes from the battery - and the things needed to have that ability were identified through an FMEA exercise which in turn incorporated data and eschewed anecdotes whether positive or negative - hope and fear are not engineering principles. And based on my research, experiments, and operating experience, I would submit that the reliability of my overall electrical system is on par with a similar system incorporating a lead acid battery.
If there is hard evidence to suggest that such a battery is indeed more of a risk when installed in a properly designed system, I'd be interested in seeing it to see what I may have missed.
With a lead-acid battery usually the ignition source is external. Perhaps the most common event is connecting jumper cables directly to the battery immediately after depleting the charge, e.g. generating a bunch of hydrogen. The negative charge lead clamped to the post is a dead give away here. If ya gotta connect to the post use the little plug in doo-hicky and turn the charger on after hooking up everything. And even then use PPE.
I thought that Shorai and EarthX had the same LiFePo chemistry, possibly even the same exact cells at least in some revisions.
Same chemistry, different cell design (according to Shorai). The EarthX adds their proprietary BMS which apparently costs as much as the rest of the battery.
I've never seen a lithium iron battery "detonate". Lithium polymer batteries are a whole 'nother animal.
As the manufacturer stated, there are only 2 causes for that behavior. Pulling too much power out, and putting too much power in.
On all my electric RC models I have battery chargers specifically designed to charge and balance each cell in the battery individually. The chargers are designed so they can't possibly over-charge a battery.
In every electric airplane I own, I have regulators that don't allow the system to over draw the battery. It also shuts the battery off when the lower threshold voltage reaches the critical level.
You can buy these chargers and regulators for any size battery. If you are handy with schematics and a soldering iron you can build your own.
Never, ever, EVER connect any kind of lithium battery to a charger or a regulator designed for lead acid batteries.
What is the exact issue?
I have lithium iron batteries in two of my motorcycles, and routinely hook them up to a 4-gang BatteryTender in my garage. To no apparent ill effect.
Not arguing, just wondering.
Charging voltages and currents are different.
But some Lithium batteries (of various sorts of "Lithium" since there's no such thing as one chemistry for Lithium batteries) have their own charge circuitry to limit said voltages and currents to what the cells actually need / require to be safely charged.
The correct answer is always: Follow the manufacturer's instructions.
Just like any battery of any chemistry.
And know that there's unscrupulous manufacturers who have very little liability if your garage, RV, airplane, or anything else -- burns.
A battery tender (usually) is a "smart charger" and won't push to much into the battery. An Alternator\regulator or a standard battery charger (dumb chargers) doesn't monitor the battery very effectively. You tell it put out 10 amps, and it puts out 10 amps. Resistance in the battery increases, causing more heat, until it detonates.
many if not all LiOn batteries have built in safety circuitry to prevent over and under charging. The larger issue is latent defects that happen during manufacturing.....those later cause internal shorts. When they rear their ugly heads it's a hot mess.
Here are some links. The first one addresses Shorai and a Battery Tender specifically. Scroll down to find it. Note the common advice in the two links. Limited charge voltage and no desulphating mode. That eliminates most smart chargers. The second link has a chart that shows which chargers are okay or not. Battery Tender-okay, Battery Minder-not okay. Beware! I bought an Optimate charger from EarthX for maintenance charging.
Yeah, that's a whole lot of nope.
Yeah I get there are safeguards, but the failure mode for lithums just isn't acceptable for me, I like my plane and life enough that the small advantage of switching is not nearly worth it, AGM for me.
I'm sure y'all be fine with the "safe" ones, but I wouldn't fly with one.
There have also been times when for whatever reason, be it right or wrong, I asked a lot of my battery, normally it occurs out in the middle of nowhere, with my AGMs and even wet batts, worse case I run it flat, having to worry about it going all 4th of July if I ask too much of it, that's not something I want to have to think about.
Boeing did more than just put the two batteries into armored boxes. They changed the battery chemistry and improved the failure protection between individual cells. It's because of these improvements that they've never needed the containment features of the boxes.
IIRC there are something like 800 787s in service all over the world currently. There has not been a single instance of battery fire to my knowledge since the original JAL incident.
The performance and economics of the 787 speak for themselves; the dash 8 variant can take a full load of pax immediately to FL410 and easily cruise at Mach 0.86 with the fuel burn of a much smaller aircraft.
They are nifty.
Not my comment, but from folks in your biz, who say the 767 was much cheaper up-front and did the same job more profitably with better dispatch rates... but everyone's enamored with the 787... so...
I didn't look into their claim, but wondering what you think.
The 787 is truly a money printing machine on long "thin" routes. If you're flying it from the east coast to say London or even Paris you might as well stick with the tired old 767. On longer legs like United's DEN - NRT and LAX - SYD the 787 really shines. The 787 is beating out the Airbus 350 in terms of efficiency (even though I like Airbus cockpit better).
The 767 does not have the range or speed and it has a higher overall fuel burn than the 787. When I'm in a North Atlantic track in my 777 at FL370 cruising at Mach .83 and I see something on the TCAS passing me up at FL410 in my same track I used to think Citation X - now most likely it's a 787.
Makes sense. These guys were saying that even a new 767 would be 1/3 the acquisition cost. I suspect they were talking old pricing vs today, but I'm not up on what airliners run at the mini-mart these days... pretty sure my credit card won't swipe that high.
Well just keep in mind a few years ago fuel was expensive and capital was cheap. So buying new fuel efficient aircraft looked good. Now with the advent of "Shale 2.0" and increased costs to borrow capital suddenly buying used airframes looks good.
Yup. But they weren't talking used, I'm probably not being clear on that part. They were talking comparing Boeing's new price for a 76 and a 78.
Fuel prices certainly do make up a big deal of the already made decisions, though.
By the way...
"Lithium Batteries Explained" online EAA webinar, May 31st.
Wings and AMT credit for it also... and free...