Revision 6 HC900 Process & Safety Controller User and Installation Manual 203
21 April 2017
Battery Installation/Replacement
Advisory Regarding Battery Installation
Memory for the CPU in the Controller Module includes:
Volatile memory and
Non-volatile memory (Flash)
Only volatile RAM requires battery backup.
When power is applied to the Controller Module, the CPU is initialized automatically. If the batteries are is
installed after initialization, and if site power is maintained, the current draw from the battery is very low -
approximately 4 microamps. If site power is disconnected with the batteries in place and with the CPU in
the initialized state, the current draw on the battery is approximately 6 ma for C30/C50 and 9 ma for
C70/C75 CPUs. However, if the battery is installed before power is applied (and the CPU initializes), the
SDRAM will draw approximately 40 milliamps.
At the 4 microamp level, the battery will retain energy over an extended period.
At the 6 to 9 mA level, the battery will retain sufficient energy to maintain the content of SDRAM for 30
days for C30/C50 and 20 days for C70/C75 controllers of backup service.
At the 40 milliamp level, battery life is severely reduced. The battery could be rendered useless in less than
60 hours.
CAUTION
Installing the backup battery when the CPU is not initialized will cause undue battery drain.
Do not install or replace the backup battery until after site power is applied.
Note: Upon power up of a controller which had been powered down with a marginal battery, the
initial battery test result will latch and hold for three minutes. This is done so that subsequent
battery checks will not falsely indicate “Good”, should the battery voltage recover after removal of
the load. After the 3 minute wait period, battery removal and replacement with a new battery will
restore the battery diagnostic to Good and reset the battery life accumulator.
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