One of our aircraft manufacturers sent this alert to us today and thought it was important information to pass on. It was a mandatory alert sent out on May 29, 2015 by Rotax concerning the use of lithium batteries in aircraft.
What I found exciting and interesting is they actually copied verbatim from our spec's and website the features the BMS must have to be approved.
Here is a copy of the alert:
NEW RELEASE
MANDATORY
ROTAX 912i (series)
ALERT SERVICE BULLETIN:
"The use of lithium-ion batteries in combination with the ROTAX Engine Type 912 i Series"
ASB-912 i-005iS
ROTAX 912iS & 912iS Sport aircraft engines are approved for operation with lithium-ion batteries if the aircraft has been equipped with a suitable battery management system (qualified by the aircraft manufacturer).
This requirement has been specified in the 912 i (series) installation manuals since Edition 1 Revision 2. The purpose of this bulletin is to bring this to the attention of users of engines delivered with earlier (Rev.0 or Rev.1) versions of the installation manual.
This is a MANDATORY alert service bulletin, and users of lithium-ion batteries should verify that their battery includes a suitable battery management system BEFORE THE NEXT FLIGHT.
WHY USE A BATTERY MANAGEMENT SYSTEM?
Lithium batteries are fundamentally different than lead-acid batteries. If overheated or overcharged, Li-Ion cells are prone to accelerated cell degradation and can catch fire or even explode. The lithium cells inside the battery need electronics to monitor and balance the voltage & charge level of the individual cells.
Some older types of lithium batteries require an external balancing charger, which you have to plug in periodically to ?top off? and balance the cells. These kinds of batteries are NOT approved.
The more modern lithium batteries have a built-in microprocessor Battery Management System (BMS) that continuously monitors the charge level of each cell and balances the charge when needed, protecting the cells from overcharge or over-discharge. Some can also provide short circuit protection, and excessive cranking protection.
Typically, the individual cells in a battery have somewhat different capacities and may be at different levels of state of charge (SOC). Without balancing, the cell of smallest capacity is a "weak point", it can be easily overcharged or over-discharged while cells with higher capacity undergo only partial cycle. For the higher capacity cells to undergo full charge/discharge cycle of the largest amplitude, balancer should ?protect? the weaker cells; so that in a balanced battery, the cell with the largest capacity can be filled without overcharging any other (i. e. weaker, smaller) cell, and it can be emptied without over-discharging any other cell. Battery balancing is done by transferring energy from or to individual cells, until the SOC of the cell with the lowest capacity is equal to the battery's SOC.
A full battery management system (BMS) might include active balancing as well as temperature monitoring, charging, and other features to maximize the life of the battery pack.
Bottom line: if you use a lithium battery in your aircraft, make sure it includes a built-in Battery Management System.
Here is the link to the actual alert:
http://legacy.rotaxowner.com/si_tb_info/alertbulletins/asb-912i-005is.pdf
Kathy