Garmin GPS 24xd Receiver and Antenna Technical Reference for Garmin NMEA 2000 - Page 8

Power Distribution and Balance Selecting the proper location of the power connection to the NMEA 2000 network depends on the length of the backbone and the power needs of the devices on the network. For the NMEA 2000 network to work properly there must not be more than a 1.67 Vdc drop in the supply voltage between the T-connector with the power cable and the NMEA 2000 device located farthest from this Tconnector. To determine the voltage drop in your NMEA 2000 network, use this equation: Voltage drop = Resistance × Distance × Load × 0.1 Voltage drop Cable resistance Distance from the = (ohms/m) Garmin cable resistance × power connection to the furthest device (in value = 0.053 meters) Network load × Sum of the LEN numbers from the power connection to the end of the network × 0.1 Voltage drop = resistance × distance × load × 0.1 Resistance: Refers to cable resistance (ohms/m). The Garmin cable resistance value is 0.053. Distance: Refers to the distance from the power connection to the device located furthest away on the network (in meters). Load: Refers to the network load. The network load is the sum of the LEN numbers of all devices from the power connection to the end of the network. When evaluating the results of your calculation, consider the following: • If you calculate a voltage drop of 1.67 Vdc or less, you can connect power to either the end or the middle of the NMEA 2000, and it will function correctly. • If you calculate a voltage drop of more than 1.67 Vdc, you must connect power to the middle of the NMEA 2000 network. The location of the power connection in the network depends on the network load and distance from the battery. You should try to balance the voltage drop equally on both sides of the power connection. • If a voltage drop of under 1.67 Vdc is not possible on the NMEA 2000 network, contact a professional installer for assistance. End-Powered NMEA 2000 Network Designed Correctly Power cable Length = 2 m Drop cable Length = 2 m Drop cable Length = 6 m Drop cable Length = 4 m 8