Aircraft

Lithium batteries

Safety, Batteries

Monday 31 October, 2016

Members should consider that, in some circumstances and designs, the charge controllers associated with the permanent magnet alternators used on some engine types offer no form of voltage control. They function by allowing sections of each half wave to pass to the battery at full output current and unlimited voltage at a frequency of up to 1,200 Hz.

The time interval of each charge pulse is varied by the regulator in order to regulate the charge condition. LiFeP04 batteries cannot be safely exposed to charging voltages in excess of 14.8 volts. Independent tests conducted by some of our members on these charging systems show the voltage output exceeds 30 volts at full power.

Lead acid batteries can be safely charged using systems where the current amplitude can be time limited on each half cycle and are immune to the applied voltage peaks.

A secondary risk is that LiFeP04 cells have an inbuilt safety switch which will open circuit the cells if the voltage reaches a critical danger level. While this switch will prevent the cell becoming unstable, it results in the high voltage spikes passing from the regulator directly to the instrument panel without the battery moderating the voltage spikes and will quickly destroy components such as radios, transponders, glass panels etc. Schicke Electronics GMBH has developed a safety switch system which disconnects the alternator from the regulator when this occurs, in order to protect the panel instrumentation.

RAAus owner-maintainers and L2s are reminded to seek the appropriate support documentation from a light sport aircraft manufacturer before fitting or using lithium iron phosphate batteries. Owner-maintainers and L2s of other RAAus aircraft are also reminded to review battery documentation and seek appropriate guidance and information before planning to use this new battery technology.