January 20, 2001 

The End of Discharge voltage for lead acid batteries is preset at the Christie factory at a point which will give erroneous results when capacity checking lead-aid aircraft batteries. 

The result of this erroneous setting is that serviceable batteries that are fully airworthy and meet or exceed the emergency capacity requirements of the FAA and the aircraft manufacturer are rejected because the end point voltage is higher than the industry standard. 

Emergency or essential capacity test requirements for airworthiness are based on the one hour rate (C1). There are two standards which have been used over the years for the end of discharge voltage at the C1 rate. The first of these is based on the general military specification for aircraft batteries and the second is based on the International Electrotechnical Commission (IEC) standard for aircraft batteries. 

Both Mil-B-83769 and later Mil-B-8565 use an end of discharge voltage at the C1 rate of 1.5 volts per cell. However, Mil-B-8565 also uses a 1.67 volts per cell requirement for certain specific battery types. 

The IEC standard uses an end of discharge voltage of 1.67 volts per cell. 

Concorde's commercial Valve Regulated Lead-acid Batteries are rated in accordance with the IEC standard. Concorde's commercial Dry Charged batteries are rated in accordance with Mil-B-83769. All military specification aircraft batteries are rated in accordance with the appropriate military specification including the specific requirements for each battery type which my differ from the general specification. 

The following chart summarizes the Christie factory settings as well at the military specification and IEC end of discharge voltages. 

Battery Voltage Military Specification IEC Christie Setting
6 V 4.5 V 5.0 V 5.4 V
12 V 9.0 V 10.0 V 10.8 V
24 V 18.0 V 20.0 V 21.6 V
28 V 21.0 V 23.4 V 25.2 V

The user should recalibrate the end of discharge voltage on the Christie RF80-K by following the instructions provided by Christie on the Service Bulletin RF80-K dated 06 March 2000. This is a pdf file which requires Adobe Acrobat Reader. 

Concorde will not warrant batteries tested on an RF80-K that has not been calibrated to either the military specification or IEC end of discharge voltage and tested in accordance with the Instructions for Continued Airworthiness (ICA) for the appropriate class of product. 


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