Hi Tony Do you have internet links to the incidents to which you refer? I would like to read about what caused the incidents as I am currently considering buying one of these batteries and have a few colleagues who have already purchased them.
Cheers Gavin Magill Auckland NZ On 16 July 2014 11:02, Tony King via KRnet <krnet at list.krnet.org> wrote: > Be very careful with any kind of lithium batteries, including LiFePO4, in > aircraft. I had a Ballistic EVO2 LiFePO4 battery in my aircraft for about > 80 hours with no issues, but I have now removed it after the second of two > significant incidents (one fatal) in Australia caused by LiFePO4 batteries. > I just didn't want to be worrying about it while in the air - especially > since the battery is directly under the seat in my aircraft. > > It's true LiFePO4 is a lot safer than LiPo batteries, but their technical > requirements, discharge characteristics and failure modes are quite > different to lead acid batteries and not well understood by most aircraft > owners. They do not like being heavily discharged and over-voltage during > charging is a definite no no. Typical solid state regulators use pulse > width modulation to achieve a well regulated average voltage, but the > voltage of the pulses is whatever the alternator puts out - which can be as > high as 22 volts, well above the 14.6V limit of LiFePO4 batteries. > > These batteries are being marketed as direct replacements for lead acid and > it's true that for their weight they make great starter batteries. But the > marketing doesn't address the differences with lead acid in any way and the > potential for a fire or the discharge of toxic gases (e.g. hydrogen > flouride) exceeds my comfort level in an aircraft, although I'd use one in > a car or motorbike or the like without hesitation. > > Another aspect that doesn't seem to be well understood is that while a lead > acid battery shows a gradual drop in voltage as it's discharged, lithium > batteries will hold close to the nominal voltage until quite deep in the > discharge cycle and then the voltage will drop very steeply to below useful > levels. This has implications in the event of alternator failure if you're > counting on the battery to run the panel or the ignition. By the time a > drop in voltage is noticed, there's very little time left. > > You might notice too that the marketing for lithium batteries tends to > focus on the cold cranking amps of lithium compared with lead acid and on > that basis lithium batteries look great. But the actual amount of energy > stored in the battery is a lot lower (typically around a third) than a lead > acid battery of equivalent cca performance. This means the lithium battery > won't be able to run a given load (say a glass panel or a radio stack or an > electronic ignition) for as long as a lead acid battery with equivalent > starting performance. > > On the surface these batteries are a great development, but the marketing > that says they're a drop in replacement for lead acid batteries is > misleading. There are several factors that need to be well understood if > you're planning to put one in an aircraft. > > Cheers, > > Tony >
