On Tuesday, May 17, 2016 at 9:58:47 AM UTC-7, SF wrote:
During the winter of 2009 I was bored, and aggravated with the sealed lead acid batteries that I was using in my sailplane. They didn't hold the voltage above 12v for very long, they needed replacement every few years, and I had one die 5 miles away from the airport at the end of a 300K badge flight. My argument that I had 2,000 FT over final glide at that point didn't sway the FAI from rejecting that flight for my badge attempt.

My search at the time led me to the K2 (Lithium Iron Phosphate chemistry)batteries that were the subject of my spring of 2010 battery article in Soaring.

Reaction to the article was mixed, and a partial retraction was printed the following month after an FAA DER (Designated Engineering Reviewer)with experience in certifying Lithium Ion batteries for some type of usage in commercial airliners, objected to the use of Lithium Iron Phosphate batteries in sailplanes because they hadn't been certified for that use by the FAA.

It's now 2016, and I see a lot of K2 batteries in other sailplanes. Soaring supply companies in the U.S. seem to be providing K2 batteries or a similar battery from a different manufacturer on a regular basis. The K2 battery I purchased in 2009, and it's twin purchased a year later, are still providing power to my sailplane without incident. There seems to be no degradation in performance, and other than switching to Anderson Power Pole connectors, I have not made any changes to my battery set up.

Has anyone out there had an issue with the usage of Lithium Iron Phosphate chemistry batteries in sailplanes?

Just curious because, a lot of dire consequences were predicted after my article came out.

SF


Here is a link to a comparison I ran three years ago for new K2 9.8Ah LiFePO4 batteries versus Powersonic 10.5Ah SLA batteries (these are the ones that are slightly taller). I used a programmable battery tester that permitted me to simulate normal base load plus occasional radio transmissions. My caseload in around an amp IIRC.

You can see the K2 batteries have a flatter and longer discharge profile. I repeated the test after three years of use for the K2 batteries. I didn't notice any significant degradation in capacity. Note that the flat profile means both that normal "capacity remaining" indications on your soaring instruments will not be accurate (at all - even if you have an option for LiFePO4 the flat voltage profile makes it challenging to estimate). Also, if you set a voltage threshold for a low battery warning it normally indicates that you have perhaps 10-15 minutes left because of the steep falloff, so you need either to be more vigilant or slave two batteries together (I use diodes to separate the batteries - just in case). For most people who don't have panels that draw an amp or more, don't talk incessantly on the radio and/or don't to 8-hour flights, capacity ought not be a problem.

https://drive.google.com/drive/folde...U9Mem5QcTBMQnM

9B