PCC-IV Instruction Manual (rev. 0.2)
Page 2-6
Section 2 - Installation
24 Vdc & 5 Vdc Power Supply Load Calculations
The PCC-IV CPU board is powered by an external 24 Vdc power supply that must be rated as a minimum for
(450 mA + field loads + option board loads). 450 mA is the load for the CPU Board + the face plate + a 25% safety
factor. Additional load is added by option boards, 4-20 outputs, and field devices. The PCC-IV is only limited by the
rating of the external power supply and/or the PCC-IV 1.6A fuse F1. Below is a worksheet to calculate precise 24
Vdc current load, if necessary.
Item
mA
each
Qty.
Total
2-wire 4-20 mA Transmitters
that are powered by PCC-IV
20
4-20 mA Outputs
(CPU +
“F” board(s))
20
Relays
(CPU + “J” board(s))
25
“B” Isolated Input board(s)
55
“G” Triac Board, 24V 5Vdc
Field wiring load dependent
50 max.
“S” Triac Board
0
“Z” Oxygen Analyzer Interface Board
45
Total mA Load:
Notes:
1) Only count 4-20 mA outputs and relays that are being used.
2) Each “B” board draws 55 mA regardless of how many input channels are being used.
3) Example: a PCC-IV-BF00 that is configured to use: (3) 4-20 mA outputs, (6) 4-20 transmitter inputs, 2 relay
output
s, plus “B” board 55 mA internal load adds a 285 mA load. Therefore, a 735 mA (minimum) power
supply is required.
A safe rule of thumb is >1A for a PCC-IV with 3 Option Boards with all 24Vdc field loads in use.
4) An external 300 mA fast-acting fuse for field +24 Vdc loads is recommended.
5) The CPU has a 5 Vdc / 50 mA power supply for field devices
(feedback pots, etc.). Each “G” option board also
has a separate 5 Vdc / 50 mA power supply. Note the “G” board 5Vdc current usage adds to the 24 Vdc
current requirement.
6) Verify that the power supply used is rated for the required mA load at the highest expected ambient
temperature. Some power supply mA ratings must be de-rated significantly above 40C (104F).
Fuses
Every PC board in the PCC-IV that uses a fuse is shipped with one spare fuse attached to the PC board
(see drawings on pages 2-9 thru 2-10 for fuse locations). Fuses used in the PCC-IV include:
Board
Service
Amps
Type
Preferred
Part Number
CPU
+24 Vdc power input
1.6 A
Slo-Blo, Radial
, 0.2”
pitch
Littlefuse 39611600440
or equal
92703
“G” and “S” Triac
option boards
24-120 Vac power to Triacs
3.0 A
Normal Blow
250 V, 5x20 mm
92247
F1 = CPU Fuse
F2 = Spare Fuse
