Dynamic DX Power Module PMB Installation Manual page 24

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Due to signal distortion that increases with increasing DXBUS length, the total
length of all DXBUS cable must not exceed 15 metres in any topology.
Two of the DXBUS's four cores (DXB+ and DXB-) are used to supply power to
the modules and to the loads connected to them. A Positive Temperature
Coefficient (PTC) device in the Power Module limits the total DXBUS current to
12 A, to protect the DXBUS wiring and connectors. The topology and cable
lengths used may reduce the DXBUS's upper limit to below 12 A.
For correct DX System operation the voltage drop on the DXBUS's DXB- wire
due to return currents, must not exceed 1.0 V between any two modules within the
DX System. Use a topology and module placement that reduces this voltage drop
as low as reasonably possible.
Voltage drops occur along the DXBUS due to the return of current back to the
battery through the small but finite resistance of the DXBUS cable and connectors.
A DXBUS connector can be modelled as:
R c t
R c t
R ct = contact resistance = 5 mOhm
R ca = cable resistance = 12 mOhm / metre
R c a
R c a
DXBUS Cable Model
19
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