Data Sheet

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MBH88 - 8 Channel, MODBUS Relay Module.

Technical Documentation

Overview

The MBH88 is supplied in a DIN rail mounting case, and provides eight optically isolated

inputs and eight volt free contact relay outputs with a current rating of up to 16Amp each.

Eight isolated inputs may be used as volt free inputs (ie. direct connection to switches or

sensor contacts) or as voltage inputs (5-24vdc).

The module is mains powered via an on-board isolated universal power unit. Control is by a

MODBUS RTU RS485 interface with even Parity or No Parity, baud rates of 9600, 19200,

38400 or 115200, and an address range of 0 to 127. The full MODBUS specification is here.

All relays have snubber circuits across the normally open contacts and are suitable for

inductive loads such as motors, solenoids etc.

Operating Temperature

-25C to +50C

Line (Mains) Power.

Universal input: 90 – 264Vac, 47-63Hz

Summary of content (7 pages)

PAGE 1
MBH88 - 8 Channel, MODBUS Relay Module. Technical Documentation Overview The MBH88 is supplied in a DIN rail mounting case, and provides eight optically isolated inputs and eight volt free contact relay outputs with a current rating of up to 16Amp each. Eight isolated inputs may be used as volt free inputs (ie. direct connection to switches or sensor contacts) or as voltage inputs (5-24vdc). The module is mains powered via an on-board isolated universal power unit.
PAGE 2
Relay power rating If the contact load voltage and current of the relay are in the region enclosed by the solid and dotted lines in the figure below, the relay can perform stable switching operation. If the relay is used at a voltage or current exceeding this region, the life of the contacts may be significantly shortened. Load type Typical applications Rating AC1 Non inductive or slightly inductive loads 16A @ 250V A AC15 Control of electromagnetic load (>72VA) 3A @ 120V AC 1.
PAGE 3
SW4 through SW10 selects the MODBUS address of the module, 0 - 127. In the table below a 0 represents a SW OFF, and a 1 represents a SW ON. For example, if SW10 is ON and the rest are OFF, then the address is 1.
PAGE 4
Relay Outputs. Each relay has a snubber circuit across the common and normally open contacts. Snubbers protect the relay contacts from arcing when switching inductive loads such as coils, motors, solenoids etc.
PAGE 5
Inputs Each Input has two links which connect it to the isolated 12v supply. This provides a small bias current to the opto-isolator which external volt free contacts can short out. In this configuration the inputs are isolated from everything except each other as they have a common 0v connection. This is normally what you will want, however if you need an input to be totally isolated then remove both links from the pcb on that input.
PAGE 6
MODBUS Function Codes The MBH88 responds to the following MODBUS function codes. 01 (0x01) Read Coils. 02 (0x02) Read Discrete Inputs. 05 (0x05) Write Single Coil. 15 (0x0F) Write Multiple Coils. 01 (0x01) Read Coils. This function code will read back the current state of the relays. The “Start Address” must be in the range 1-8 and the “Quantity of Coils” must be in the range 1-8. Also the sum of these two parameters must not exceed 9. 02 (0x02) Read Discrete Inputs.
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Connections & Dimensions