Garmin GPSMAP 541s Technical Reference for Garmin NMEA 2000 Products - Page 10

NMEA 2000 Fundamentals End-powered NMEA 2000 network, incorrectly designed: + - Power cable Length = 2 m NMEA 2000- NMEA 2000- NMEA 2000- compliant device compliant device compliant device INCORRECT LEN = 4 Drop cable Length = 2 m LEN = 5 Drop cable Length = 6 m LEN = 7 Drop cable Length = 6 m Backbone cable Length = 20 m Backbone cable Length = 10 m When the voltage drop formula is applied to this example, we see that the voltage drop is greater than 3.0 Vdc, so this NMEA 2000 network will not function correctly when powered at the end. Voltage Drop = 0.053 × (2 + 20 + 10 + 6) × (4 + 5 + 7) × 0.1 = 3.22 Vdc Cable Distance Network load resistance This NMEA 2000 network must be redesigned with the power connected to the center of the network in order to function correctly. Middle-powered NMEA 2000 network, correctly designed: NMEA 2000- NMEA 2000- NMEA 2000- compliant device LEN = 4 + - compliant device LEN = 5 compliant device LEN = 7 CORRECT Drop cable Length = 2 m Power cable Length = 2 m Backbone cable Length = 20 m Drop cable Length = 6 m Drop cable Length = 6 m Backbone cable Length = 10 m When the NMEA 2000 network is redesigned with the power source in the center, you calculate the voltage drop in both directions. If the T-connector to which you connect the power source is connected directly to another T-connector (as shown in this example), use the LEN from that device as part of the calculation for both directions. When the voltage drop formula is applied to both the left and right Voltage Drop Left = 0.053 × (2 + 20 + 2) × (4 + 5) × 0.1 = 1.145 Vdc sides of the power source in this example, we see that the voltage drop is less than 3.0 Vdc on each side, so the NMEA 2000 network will Cable resistance Distance Network load function correctly. Voltage Drop Right = 0.053 × (2 + 10 + 6) × (5 + 7) × 0.1 = 1.145 Vdc Note: The equation and examples provide conservative estimates for calculating voltage drop.  Technical Reference for Garmin NMEA 2000 Products