DeltaV Bulk Power Supplies are used to provide 24 VDC power to the DeltaV system power supplies and to power 24 VDC field circuits. To size the bulk power supplies, determine the DeltaV system components connected to the bulk power supply and total the current draw at 24 VDC to arrive at the total current demand for the bulk power supplies. Ensure the bulk power supplies have sufficient capacity to provide overcurrent to guarantee that fuses and circuit breakers are triggered without a loss in operating voltage. In redundant applications, ensure that the power supplies have sufficient capacity to power the entire system.
24 VDC bulk power to system power supplies = ((LocalBus current * 0.5) + (# of controllers * 2 A * 0.24))/0.75
The LocalBus current is the total I/O card current at 12 VDC. You can use the actual current load based on the installed I/O cards or the maximum capacity of the system power supplies (8 Amps at 12 VDC). Be sure to allow for future expansion of the I/O subsystem.
When used to power field circuits, the bulk power supply load is determined by totaling the field power demand of each I/O card connected to the power supply. For some cards, part of the 24 VDC field power is used for internal components such as A/D converters in addition to the field signal. The field power current values that are provided in the DC current requirements for S-series I/O table are based on all signals operating at their maximum level. In the case of discrete output channels, it is likely that the actual field current draw will be less than the maximum listed in the table. For safety systems, all outputs can be energized at the same time. You can substitute the actual current draw if you know it. Also, it is highly unlikely that all signals are active and at their maximum at any given time. While this can be used to adjust the actual 24 VDC power required for your system, it is often simpler to assume maximum load and design the 24 VDC bulk supplies accordingly.