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 On 16 July 2014 02:08, brian.kraut--- via KRnet <krnet at list.krnet.org> wrote: > Lithium Iron Phosphate batteries are the way to go with aircraft. They > have near the capacity to weight and size ratio as Lithim Ion and and > Lithium Polymer, but they are many times safer. There is a ton of > information on them on the web a Google search away. The biggest > drawback to most of the Lithium varieties after getting over the safety > factor is that the cells really need to be balance charged correctly. > EarthX now has batteries that have all of the complicated charging > electronics built in the battery. I got one for my avionics backup for > the Mustang 2. I have enough capacity in just 1.3 pounds to fly IFR > until my fuel tank runs dry if I loose my primary battery and > alternator. EFIS automatically switches with its built in two power > source configuration and I have off/main/backup switches for my nav and > com radios and my EIS engine monitor. Probably will add the backup > position switch to my transponder at some point also. > > I highly recommend EarthX and many years from now when my PC680 main > starting battery goes I will replace it with a 2-3 pound EarthX. > > http://earthxmotorsports.com/ > > > > -------- Original Message -------- > Subject: Re: KR> "Engine-driven alternator?" > From: Jeff Scott via KRnet <krnet at list.krnet.org> > Date: Tue, July 15, 2014 7:52 am > To: krnet <krnet at list.krnet.org> > > If your plan is to operate a Mode-S with ES transponder, or a UAT Out > along with Mode C transponder to comply with the 2020 mandate, along > with a low wattage Comm radio, I would suggest that your lightest option > would be a light weight solar charger and either a Lithium Ion or > Lithium Polymer battery pack. The solar charged LiPo combination gives > you a lot of useful time with the avionics necessary to fly in your area > without a huge weight penalty. > > Caveat: The Lithium Ion and especially the Lithium Polymer batteries can > be a fire danger if discharged too rapidly (heavy loads like a starter) > or in a crash scenario if they are punctured. However, when I was > working in the UAV/Drone world we used Lithium Polymer batteries > exclusively and had some very high G impact crashes. The only damage we > ever saw with the Li-Po batteries was heat damage from discharging them > too rapidly running electric motors on the electric UAVs. > > While there are now Li-ion and Li-Po batteries available for aircraft, > at this time I don't recommend them as the primary battery for an > aircraft with a complete alternator/battery system. Thermal damage from > improper or high charge rates is also an issue with these batteries. > > -Jeff Scott > Los Alamos, NM > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options >
