ABB AC 900F Mounting And Installation Instructions Manual page 121

Section 8 Service
CPU module without battery
This AC 900F operating mode is recommended with regular supply voltage failures
for a longer period of time, e.g. with solar energy supply. As no energy is supplied at
night (buffering mode), the battery would be discharged within less than two years.
In order to ensure that after a control start the controller operates with the data from
the memory card and not with "partly" still available data in the memory, a
minimum turn-off time of the controller must be observed. The turn-off time
(discharge of the buffer capacitors in the CPU module) must be > 60 s.
M&I – AC 900F Controller
Update/Restore
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