LonWorks Communication Bus Fundamentals
Network Guide 61
Power Supply Requirements for 24V Controllers
About External Loads
When calculating a controller's power consumption to size the 24VAC transformer, you must
also add the external loads the controller is going to supply, including the power consumption
of any connected subnet module (for example, for Allure Series sensors). Refer to the respec-
tive module's datasheet for related power consumption information.
A controller can support a maximum of two Allure Series sensor models equipped with a CO
2
sensor. See Subnetwork Module Compatibility and Supported Quantity Charts on page 71 for
how many Allure Series sensors are supported by a given controller model. The remaining
connected Series sensor models must be without a CO
2
sensor.
For the ECL-VAV model, see the room device calculator spreadsheet available for download
from our website to determine the power requirements and supported quantities of connected
subnet modules: VAV-Smart Room Control Device Calculator.xlsm
Transformer Selection and Determining the Maximum Power
Run Length
It is recommended to wire only one controller per 24VAC transformer.
When calculating a controller’s power consumption to size the 24VAC transformer, you must
also add the external loads the controller is going to supply, including the power consumption
of any connected subnet module (for example, Allure™ Series Communicating Sensors).
If only one 24VAC transformer is available, determine the maximum number of daisy-chained
VAV controllers that can be supplied on a single power cable supplied by a 100 VA trans-
former, according to the controller’s expected power consumption including external loads, the
cable’s wire gauge, and the total cable length from the following figures (Figure 36 and Figure
37). Any installation condition that is outside of the parameters of the following graph should
be avoided.
To maximize daisy-chaining performance, the transformer should be installed as close as pos-
sible to the first VAV. If this is not possible, then use 14 AWG wire to power the first VAV which
can help reduce a voltage drop at the end of the daisy-chain.
Distech Controls' 24V-powered devices are Class 2 Products. To conform to Class
2 installation requirements, only use transformers of 100VA or less to power the
device(s).
The recommended minimum peak input voltage is 27.2V
p
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