User Manual

RECON Water Heaters Installation, Operation & Maintenance Manual
CHAPTER 8 – WATER HEATER MANAGEMENT
Page 126 of 178 AERCO International, Inc.  100 Oritani Dr.  Blauvelt, NY 10913 OMM-0103_0A
PRI: 10/28/2014 Phone: [phone] GF-147
NOTE: The WHMS Master does not necessarily have to be on either end of the Daisy-Chain loop
Figure 8-3: Typical Daisy-Chain Modbus/RS485 Network
Any one of the C-More WHM units included in the Modbus network can be the Master.
However, it is recommended that you decide which unit will be the Master and which will be the
last unit on the daisy-chain prior to performing the wiring connections. This will simplify wiring
connections and Modbus address assignments.
Modbus network wiring connections must be made using shielded twisted-pair wiring, (18 – 24
AWG) such as Belden #9841, #3105A, #8760, or equivalent. The Modbus wiring connections
are made at the RS485 COMM terminals on the I/O board included with each C-more Control
System.
Connect the Modbus wiring as follows:
Modbus Network Wiring
1. Starting at the first unit, connect the twisted, shielded pair cable to the RS485 Comm plus
(+) and minus (-) terminals on the left side I/O board as shown in Figure 8-4.
2. At the I/O board of the first unit in the daisy chain (not necessarily Master), activate the DIP
switch labeled “MODBUS TERM” by placing it in the up position. This will connect a
termination resistor across the terminals at the source end.
3. Refer to Figure 8-4 and run the shielded cable to the next unit in the daisy-chain and
connect the + and – wire leads (+ to +, - to -). DO NOT terminate the shield of the RS485
Comm leads to the SHIELD terminal at the Slave. Instead, connect the shields of the
incoming and outgoing RS485 leads together.
4. Continue connecting the + and - wire leads and shields for the remaining units as described
in step 3 for the remaining Slave units in the chain.
5. At the end unit in the chain, activate the DIP switch labeled “MODBUS TERM” by placing it
in the up position. This will ensure that the termination resistors are activated at both ends of
the loop.
WHM
MASTER
# 1
WHM
SLAVE
#2
WHM
SLAVE
# 3
WHM
SLAVE
# 4
WHM
SLAVE
# 8