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I also fly large scale remote control control gas and electric planes and helicopters, LifePO4 batteries have been extremely stable for all of the RC world but the majority of us balance charge our batteries for longevity. In the RC world life batteries have a nominal voltage of 3.3v/cell, different than the aerovoltz but the principal is the same.
Have you ever balanced charged your aerovoltz lifepo4 battery? Over time you can get a voltage differential between the cells which during the constant charging you could get a cell or two with elevated voltages that could lead to a cell failure. The aerovoltz website does mention the periodic balancing of the cells. http://aerovoltz.com/av_mgt.html |
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I agree with others... I'll stick to traditional batteries. the risk vs reward on this one is off the charts. |
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Have a read of the NTSB final report on the B787 battery fire in Boston here: http://www.teslamotorsclub.com/attac...2&d=1417522601 My personal stance is that I will not allow any large format or high-power capacity (more than a cell phone or ipad) lithium ion batteries of any chemistry in or on my airplane. Especially one that I can't chuck out the window if necessary. I suppose I do need to think about how to throw a cell phone out of my slider canopy if it were to vent. Over on the RV10 forum there was some talk recently of lithium ion battery powered jump-starters. They're certainly attractive from a weight and power perspective, but in my opinion are even more dangerous than a lithium ion battery mounted on the firewall because one would most likely store it in a flight bag inside the cabin. |
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Causes of battery failure
I don't know. I'm with Paul on this?.. let's wait for ALL the details. The pictures and story are a little suspicious. How many of us can just open a hatch and remove our batteries? Any hold down clamps? Maybe a cover or strap to remove? If I was to guess, this battery was sitting in a tray and just vibrating away for, who knows how many hours?.. MAYBE a hole got worn through the case, maybe something external shorted it out? I don't know. But, let's just get rid of all these nasty LITHIUM batteries ?.. I don't know, maybe all these "homemade" airplanes should be grounded?.. Just kidding, of course, but let's not let mob mentality take over.
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I heard that a car crashed last week. No way am I getting back in another car. They're dangerous.
Folks, let's see what the cause was. Lithium doesn't always equal fire, smoke, or an emergency. Done correctly it can have great benefits. This is experimental aviation, something I think folks forget about. We all have varying levels of comfort / risk we are willing to fly with. Those levels should be respected by everyone, not slammed because they aren't the same as your own. Flying is inherently dangerous, we just mitigate the risk and accept the rest. I for one will put a LifePo battery in my 10, safeguarded as much as possible and accept the risks just like other key components in my plane. |
Some years ago I had a new Yuasa battery blow its top off in my Harley while on a ride. Did about $5000 in damage. I contacted Yuasa, they sent me a special container to ship it to their lab for analysis. Surprisingly enough they claimed responsibility, saying they had a bad batch of batteries and the one I had was one of them. With the letter there was a check for all the damages. This Yuasa was a common lead acid battery. Point is, there's no 100% safe battery made. The first generation lithium ion batteries were unstable and got a bad reputation but there's different chemistries now with lithium, mostly very stable..... That being said, there's still some growing pains with this technology. With any battery, there's a tremendous amount of instant energy sitting there in your battery box. If something goes wrong they all have the potential to China syndrome.
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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'd wait for the full analysis if there is one before pointing fingers but the report brings home the effects of what can happen if there is a Lithium battery fire. Make no mistake, if this happens to a cabin mounted battery in flight without proper containment and venting, you will be incapacitated within seconds.
You cannot believe the amount of smoke and soot that one of these can produce when things go wrong... Design accordingly. |
Here is a update on this event:
Now that some time has passed I wanted to update everyone on the battery fire issue. This week we repaired the airplane, making a new hatch door, and relocating the battery installation from the nose to the under engine compartment. We installed an Odyssey battery. We did not replace the regulator yet, but did correct the ground wire connection that was burnt, running both power and ground wires from the regulator directly to the battery terminals to ensure a good connection. Removing the extra battery cable saved a few pounds. The odyssey battery weighs 13 lbs, so a lot more than 3.5 lbs, but a lot less than what he had. Moving the location really put the CG where we wanted it. This morning, Monday, I flew the airplane down to West Virginia. What I discovered was that with the Odyssey battery, the voltage was rising, right past 14.4 and on to over 16 volts before I turned on the landing lights to load it back down to a safe voltage. The landing lights draw close to the output of the charging system, or possibly even more. So that kept the voltage down under 12. There is no question now that the regulator is bad. I think that we can reasonably assume now that the regulator is the cause of this incident. What I find very interesting though is that when the Lithium battery was installed, the volts did not exceed 14.4. I think Jim Showker might be on to something here in that with these lithium batteries they simply cannot absorb any energy past a full charge, they simply began to overheat and if it continues, start a thermal run away. A 13-20 lb lead acid battery has a lot of thermal mass and can absorb a lot of heat, plus water boiling away dissipates a lot of heat as well if it is a flooded battery. So it is very conceivable that a lithium battery would be very vulnerable to an overcharge situation. But also, it may be that with a lithium battery there will be little indication of over charging. It seems that the lead acid battery will allow the voltage to go right on up, where possibly the lithium battery is absorbing that energy thus keeping the voltage down, not indicating an overcharge condition on the voltmeter. I don't know this to be true for sure, but it certainly appears to be the case. I will discuss this with Aerovoltz and also see if we can find some solid solutions to prevent this. Steve, the owner of Aerovoltz did call me today, but I was on a flight to Sun N Fun and could not take the call. Hopefully I'll catch up with him soon. The owner of the airplane has a key west on order and will install in ASAP! So, in conclusion for now, I think we can determine that overcharging is the cause of this incident. The el cheapo junk regulator was the culprit. Using these batteries can be done safely in my opinion, however, I would only use a very good quality regulator like key west, and consider anything above 14.0 V to be dangerous. Monitoring system voltage is a must in my opinion. And still might not be a bad idea to consider the possibility of thermal runaway on one of these when you install it. Being able to easily access it and throw it overboard would be a good idea. Keeping it away from anything flammable. Having a way to shut off the charging system in the event of an over voltage should be considered also. As long as they are not over charged there should be no issue. The questions then become, if it is overcharging, will you know it, and if so, what will you be able to do to remedy it. Remember it only took 30 minutes from a cold battery to on fire. Over voltage has to be able to be detected and remedied quickly in flight. |
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