AFGS�87219B APPENDIX A
REQUIREMENT RATIONALE (A.3.2.9.2)
Because they are a convenient source of stored energy, batteries are widely used in aircraft for emergency power, standby and fill-in power, engine and APU starting, and for limited energy requirements when no other source is available. On the other hand, batteries have limitations which have to be recognized and accounted for in order to have a reliable installation. Since chemical reactions are involved in the charging and discharging processes, battery performance is very sensitive to temperature. Other factors affecting performance and life include depth of discharge, method of charge, quality of maintenance, and type of construction. Present requirements for aircraft secondary batteries have evolved over the years as the result of experience and new technology. Prior to the issuance of specifications MIL-PRF-81757,
MIL-PRF-8565, and MIL-PRF-29595, each military service had its own procurement specifications. These separate requirements are now combined into the three coordinated specifications for nickel-cadmium, maintenance-free, and lithium batteries. Battery installation requirements were previously in DH 1-6 and DH 2-3.
REQUIREMENT GUIDANCE (A.3.2.9.2)
a. Lead-acid, nickel-cadmium, and lithium are the three types of secondary batteries most used in aircraft. Lead-acid batteries are less costly, easier to maintain, and can be effectively charged from a simple constant-potential source. Nickel-cadmium batteries, however, provide much better high-rate performance, especially at low temperature. The disadvantages of nickel-cadmium include higher cost, special maintenance procedures, and more closely controlled charging for safe and reliable performance.
b. MIL-PRF-81757, MIL-PRF-8565, and MIL-PRF-29595 are tri-service specifications for nickel-cadmium, maintenance-free, and lithium batteries respectively. These standard batteries, which are the product of considerable tri-service experience and research, should be used where suitable. They are procured competitively and in quantities which result in lower cost. Sealed-cell lead-acid batteries have been qualified to
MIL-PRF-8565. This type should be preferred over lead-acid batteries that were qualified to the canceled MIL-B-83769.
c. Both MIL-PRF-81757 and MIL-PRF-29595 specifie individual cells as well as complete batteries. Therefore, if none of the MIL-PRF-81757 or MIL-PRF-29595 standard batteries are suitable, the next best choice for a nickel-cadmium or lithium battery would be a
non-standard battery made up of either MIL-PRF-81757 or MIL-PRF-29595 standard cells.
d. In selecting a battery to meet a required ampere-hour capacity and other performance requirements, the effects of temperature, charging efficiency, aging, and other de-rating factors should be considered.
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