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 T-connector.

To determine the voltage drop in your NMEA 2000 network, use this equation:


Voltage drop	=	Resistance	×	Distance	×	Load	×	0.1
Voltage drop	=	Cable resistance (ohms/m) Garmin^® cable resistance value = 0.053	×	Distance from the power connection to the furthest device (in 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.

Correctly-balanced NMEA 2000 network example with callouts — Figure 1. 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
	Backbone cable Length = 10 m
	Backbone cable Length = 6 m

When the voltage-drop formula is applied to this example, the voltage drop is less than 1.67 Vdc. This NMEA 2000 network will function correctly when powered at the end:


Resistance	×	Distance	×	Load	×	0.1	=	Voltage drop
0.053	×	22 (2 + 10 + 6 + 4)	×	14 (4 + 5 + 5)	×	0.1	=	1.63 Vdc

Incorrectly-balanced NMEA 2000 network example with callouts — Figure 2. End-Powered NMEA 2000 Network Designed Incorrectly


	Power cable Length = 2 m
	Drop cable Length = 2 m
	Drop cable Length = 4 m
	Drop cable Length = 6 m
	Backbone cable Length = 10 m
	Backbone cable Length = 6 m

When the voltage-drop formula is applied to this example, the voltage drop is greater than 1.67 Vdc. This NMEA 2000 network will not function correctly when powered at the end. to function correctly, this NMEA 2000 network must be redesigned with the power connected to the center of the network.


Resistance	×	Distance	×	Load	×	0.1	=	Voltage drop
0.053	×	24 (2 + 10 + 6 + 6)	×	16 (4 + 5 + 7)	×	0.1	=	2.04 Vdc


	Drop cable Length = 2 m
	Power cable Length = 2 m
	Drop cable Length = 4 m
	Drop cable Length = 6 m
	Backbone cable Length = 10 m
	Backbone cable Length = 6 m

When the NMEA 2000 network is redesigned with the power source in the center, 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 the device connected to that T-connector as part of the calculation for both directions.

Table 1. Voltage Drop to the Left of the Power Connection
Resistance	×	Distance	×	Load	×	0.1	=	Voltage drop
0.053	×	14 (2 + 10 + 2)	×	4	×	0.1	=	0.30 Vdc

Table 2. Voltage Drop to the Right of the Power Connection
Resistance	×	Distance	×	Load	×	0.1	=	Voltage drop
0.053	×	12 (2 + 6 + 4)	×	12 (5 + 7)	×	0.1	=	0.80 Vdc

Technical Reference for Garmin® NMEA 2000® Products

Previous Topic

Next Topic

Download PDF

Print Page

Power Distribution and Balance