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> List-Post: krnet@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
