MKS 651D Series, User Manual, Page: 47 / 162

Chapter Three: Overview Optional Valve Failsafe Battery Back-Up
35
Note
If for any reason the controller cannot open or close the valve within 30
seconds of a power failure, the battery back-up module automatically
turns off. This prevents the battery from discharging when no valve is
present or if the valve is defective in some way.
Threshold Voltage Check
When the 651 controller is turned on, it measures the voltage at the input port assigned to the
battery back-up module. When the voltage level at the port exceeds a factory set minimum
threshold value, the controller recognizes that the battery back-up is present, and the software
menus which support the module are installed. Should the voltage level be below the threshold,
the controller does not recognize the module and the software menus are not installed.
Once the 651 unit has been powered up and the battery back-up module has been recognized,
the actual voltage of the battery is measured. Refer to
How To Check the Battery Voltage, page
42 (Local operation), and How To Report the Voltage Status of the Valve Battery Back-Up ,
page 112 (RS-232 operation), for more information.
Expected Battery Life
An AC power failure typically results in a 30% discharge of the battery. Under this condition,
the battery life is at least 1000 cycles, and should be able to recharge within a few hours after
power returns. Battery life under several conditions is listed in Table 11.
Expected Battery Life
Expected Cycles % Discharge with each Battery Use
1000 30
400 50
200 100
2-3 years if unused and charge is maintained
Table 11: Expected Battery Life
When AC power returns, the battery recharges, provided that the 651 controller is turned on.
From a full discharge condition, the voltage typically increases from about 11 V to 15.5 V over a
five-hour period. The voltage is maintained at about 14.5 V for another five hours then
gradually drops to 13.5 V. The 13.5 Volt charge is maintained in a trickle charge state (a top
charged state) until there is an AC power failure. The recharge time for a completely discharged
battery is a maximum of 12 hours.