The Primary thing builders must understand is NOT to use a Lithium Ion battery in their plane. We had a builder have a forced landing over this. Those batteries are light, and they have their fans, but I have spent a lot of time listening to the builder with the issue, and I am convinced that the internal circuitry represents an unacceptable risk on a Corvair powered plane. I am not alone in this, Dan Weseman has long said the same thing, and Builders like Ken Pavlou have removed their Lithium batteries after studying the issue.
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9 Replies to “Use the Correct Battery – Video”
William. I saw your post from 3 years ago as I was searching for Vong Sarendy. My father, USN supply corp, also was in cambodia with Vong at the same time as your father. We too have items given to my Dad from Vong and pictures of them together. Thank you for your insightful comments.
Thanks for the video.
There are supposedly newer batteries that are on their way that outperform the present Lithium batteries without their drawbacks. You can read about one here, in an enthusiastic article: https://www.texasmonthly.com/energy/all-charged-up-john-goodenough/ and https://news.utexas.edu/2017/02/28/goodenough-introduces-new-battery-technology/ Whether or such a battery actually will be better remains to be seen, and there is always a big gap between research, development, and actual production, as well as the gap between real world and lab performance. Cost is always factor.
As pilots, safety and reliability should be our primary concerns. Your video illustrates it well. AGM batteries, which Bob Nuckolls has advocated for years, are very safe and are known quantities, not dependent on any internal electronic circuitry, and can be mounted in any position. They are lighter than traditional lead acid batteries, and do not require venting.
A few years back, when looking at the AGM batteries that had been approved to replace the regular lead acid batteries on Pipers and Cessnas, for some reason, the approved AGM batteries were not much lighter than the traditional lead acid batteries they replaced. The Odyssey that will handle the same load is much lighter and smaller, but it isn’t approved for aircraft certificated in the Normal category.
When I read Bob Nuckoll’s postings on AGM batteries, which he advocates, I remember that he would test his AGM battery’s capacity new by subjecting it to a fixed load and determining the time it would take until the voltage dropped to a predetermined level, then annually test it again to determine it’s real world remaining capacity.Bob seems to test EVERYTHING electrical.
The question each of us should ask ourselves is, “Is a few pounds in weight savings worth the risk?”
Good presentation. And a reminder that if you don’t know what you’re messing with, you probably ought not to be messing with it — or at least be prepared to learn things the hard way, which is inadvisable in aviation.
I design electronics for a living, and over the years I’ve designed plenty of lithium-ion battery charge control circuits. And I can safely say that they’re not trivial. Like all batteries, as Li-ion batteries move up and down their discharge curves, the curves themselves move a little as a consequence of component aging. With most battery technologies, this doesn’t matter, since you can be pretty close to knowing when it’s topped off and be perfectly okay. Not so with Li-ion, which internally have spots where the charge/discharge becomes highly exothermic. Handle one wrong, and you start a fire with it. This is why many of these batteries have (for obvious safety reasons) built-in thermistors (usually negative temperature coefficient type). And most good charge controllers have inputs for the thermistor output so what’s going on chemically inside the battery can be cross-referenced to the record of the last charge/discharge cycle curves.
Get all that right, and Li-ion batteries are great. But getting all that right is well beyond the skills of the average homebuilder. And it has a single point of failure (the NTC thermistor) that can wreak havoc when it goes out, since you lose the ability to detect an incipient fire in the battery and back off before it ignites.
As I said, I’ve designed charge controllers for Li-ion batteries plenty of times in my life, and they’d be the very last battery technology I’d use in an aircraft. A camcoder, absolutely. But rarely does anybody die when a camcorder quits.
For my own plane, an absorbent glass mat battery makes a lot more sense.
Eric, Good analysis.
In simple terms, (from the EarthX user’s manual)
A Lithium Ion battery will disconnect from providing power and show “No-Voltage” when it is discharged to just 11.5 volts. So, in other words, in the event of a charging system failure, your fancy battery quickly becomes a light weight brick.
The 10-Lb weight savings comes at the expense of a less reliable battery that will provide no help in the event of an emergency. Never trade anything for reliability. Besides its easier to take 10-Lbs off the pilot that off the airplane.
In ideal conditions, the Lithium battery would take a while to drop to the 11.5 cut off, but the primary issue is having the internal circuit decide it will cut off right away. This is what happened on the plane that had the forced landing. It had a working charging system at takeoff, it popped a breaker on the charging system, which would have left it hours of energy on an Oddsey battery, but the Li battery was showing 12.5 V and cut off in less than 10 minutes. The presumed explanation is the circuit internal to the battery decided this for some reason. We don’t have computers to run the corvair, why have one inside your battery to shut it off?
Not having all the data in front of me, I can’t do any serious post-mortem. But one of the potential failure modes of Li-ion is for the “intelligence” of the battery to detect something that’s suddenly outside of its expected charge/discharge curves and go to a failsafe where the battery shuts itself down completely. The rationale is that the sudden change in voltage/impedance on the other side of the battery node could be what starts the endothermic chemical reaction that eventually becomes a fire. From the battery’s point of view, it’s doing the most sensible thing: Preventing a fire. From the user’s point of view, it’s doing the worst thing imaginable: Depriving a mission-critical system (such as engine ignition) of power. But a battery designed for your digital camera has no idea that it’s going into an airplane. And the designers of it likely wouldn’t sell it to you if they knew that’s where it was going.
When you pop a breaker, you’re instantaneously changing an impedance that was probably quite low (after all, it was high current flow that caused the breaker to want to pop in the first place) to one that’s suddenly infinite at that node (since it’s become an open circuit). There aren’t too many more drastic changes in impedance than that, and it’s highly likely that’s what ticked off the battery’s internal charge control and safety circuits.
If the manufacturers of batteries are tight-lipped about how their charge controllers work, you can largely thank the lawyers. A lot of the data I have on Li-ion battery charge control algorithms I only get because I’ve signed non-disclosure agreements with the manufacturers and am obligated to protect these things like my own trade secrets. To some degree, bleeding every last electron out of battery is a highly competitive business. (You can thank portable electronic devices for that.) But in the case of Li-ion, which is a known potentially flammable technology, there’s huge liability involved. And the less a battery manufacturer says publicly about how it does things, the lower its liability exposure when a fire starts or an airplane crashes. So precisely the data you’d like to have to do proper design is precisely the data the corporate attorneys want to make sure you don’t get.
Li-ion has its use. Think: “Camcorders.” Be extremely hesistant to think: “Electric cars.”
Don’t think “airplanes” at all. Stick with absorbent glass mat batteries, there. Or at least lead-acid if you can’t afford AGM.
Hey William, what do you think about using a second separate battery isolated from the main buss just for the ignition system? If you think it is a good idea what battery would you use?
A backup battery is a good idea if you have the space for it in your plane. I use a small 6 amp hour AGM battery as a backup. It is isolated from the main buss and only the points side ignition and a fuel pump is connected to it.
I would just use one good AGM.