Programming instructions

22
How to compute power drain of the power supply
As has been stated before, the power supply can only support a certain
number of extension block and special function blocks.
In the case of the FX3U, a power supply, FX3U-1PSU-5V can be added to
offer additional bus voltage. This power supply creates 1A of 5VDC and
300mA of 24VDC. It is recommended to use this module after discrete I/O
extensions as they require high amounts of 24VDC. Up to 2 can be used
on a single FX3U system.
To determine if your system has a legal configuration, follow the steps
below.
1) Total up the number of inputs and outputs you want to add to the
main unit. Note that when a powered extension unit is used, all
I/O points following it are calculated as a separate system. Each
16 input points require 100mA of 24VDC, and each 16 outputs
require 150mA of 24VDC. Look at Table 1 or 2 for the PLC type or
Table 3 or 4 for a powered extension unit. Cross-reference the
input column with the output column. The number found is the
remaining current.
2) Take note of the discrete I/O extension blocks, SFMs, expansion
boards, and special adapters in the system. Look up the 5 VDC
and 24 VDC current consumption ratings in Table 6. Where there
is a listing for external 24VDC, this means the unit has terminals to
connect an external power supply. In this case it does not need to
be added to the internal consumption, unless the external wiring is
connected to the 24VDC output terminals on the PLC.
3) Look at Table 5 to determine the amount of 5 VDC current
available. Tables A1 and A2 are FX3U main units, and table D1 is
powered extension units.
4) Add the module consumption and subtract from the available power
supply.
NOTE: These tables are in the FX3U Hardware Manual (part number
JY997D16501), Chapter 6.