Intelligent RS-485 and RS-422 Adaptors
4
Power Supplies
The Intelligent RS-485 and RS-422 Adaptors require 9 to 18 volts DC
at 100mA, normally supplied by a 9v DC 300mA plug pack power
supply, via a centre-positive 2.5mm DC connector. The adaptors are
protected from reverse polarity by a 1A series diode.
The Intelligent RS-485 and RS-422 Adaptors can be configured (via an
internal jumper) to supply unregulated DC voltage (from the plug pack
powering the adaptor) to the RS-485 and RS-422 connectors. The
maximum current that can be drawn in this way must be limited to
either 500mA, or 100mA less than the capacity of the plug pack,
whichever is the smaller. Note that this output is not fused or protected.
Using the recommended MCP-2S cable for RS-485 installations and
MCP-3S cable for RS-422 installations provides for a spare pair of
wires. In some installations, it will be possible to use this spare pair to
provide power over the cable to the networked units, either from the
Intelligent RS-485 and RS-422 Adaptors (see above), or from another
power supply.
The following points should be noted:
•
The ASPNet Terminal and the Networked Portable BCR both
require 9 to 18v DC power. All other units will accept either 8 to
16v AC or 9 to 18v DC power.
•
The voltage drop can be very high, especially if the cable run is long,
or a large number of units are being powered. You must ensure that
sufficient power reaches each unit.
•
As a simple “rule of thumb”, each unit requires approximately
100mA of current.
•
In anything other than a very small network, it will most likely be
necessary to use more than one power supply, each powering a
number of units on a segment of the cable.
