Dealer Certification
Section 2: Building the Network
Physical Planning & Documentation
Power Sources & Distribution
Voltage Drop Calculations
Copyright © 2011 NMEA
Physical Planning & Documentation:
Power Application Example
Physical Planning & Documentation:
Planning the Physical Layout
 Determine Device Locations on the vessel
 Determine Backbone Path through the vessel
– Passes within 6 m of Each Device
– Less than 100 m End to End (250 m w/heavy cable)
– Backbone Must Not Branch
 Determine Power Source and Application Point(s)
Physical Planning & Documentation:
Planning the Physical Layout
 Select Cable Type
– Either Light (Most Common) , Mid or Heavy
– Ensure Total Power Does Not Exceed Cable Rating
 Determine Power Source and Application
Point(s)(Power Tees)
 More than one power application point IS allowed and
MAY be needed as network size increases.
Physical Planning & Documentation:
Start With a Backbone Diagram
1. The length of each network segment and drop
cable; location of tees and terminations
2. The identity and network LEN of each
equipment on the network
3. The planned location(s) where power will be
supplied to the network
4. The single location where the shield/drain wire
will be connected to vessel’s non-current carrying
RF ground.
Physical Planning & Documentation:
Start With a Backbone Diagram
A completed network diagram contains all
information necessary to complete the voltage
drop calculations
Defines all cables, connectors, & devices needed
for the complete installation
Physical Planning & Documentation:
Load Equivalency Numbers (LEN)
 Representation of the amount of current a device
uses from the bus
 All devices have a LEN equivalency number (LEN)
 The device manufacturer publishes this number
Physical Planning & Documentation:
Load Equivalency Numbers (LEN)
 1 LEN = 50mA , 20 LEN = 1 Amp
 Maximum LEN a single device can power from bus = 20
 LEN is used to determine the voltage drop
 The higher the LEN, the higher the voltage drop
Physical Planning & Documentation:
Less Than 5 Devices
 NMEA 2000® Backbone Provides Power to Devices
 Network Devices Require 9 to 16 VDC
 Most NMEA 2000 devices get power from the bus
POWER INSERTIOIN POINT
Physical Planning & Documentation:
5 Or More Devices
2 meters
0.3 meters
0.3 meters
POWER
2 meters
6 meters
0.3 meters
0.3 meters
5 meters
2 meters
2 meters
Power Distribution:
Backbone Electrical Connections
 Power Source Options
–
–
–
–
Ships Battery Connection (12.5 VDC)
Isolated DC to DC Power Supply (13.8 VDC)
Isolated AC to DC Supply (13.8 VDC)
Multiple Power Supplies (13.8 VDC must be consistent)
 Backbone Shield Connection
– Only Connected at a Single Point (Single Power Tee)
– Connected to the non-current carrying RF Ground
Power Distribution:
Power Source Considerations
 Voltage Drop on Backbone Limited by
– Voltage Available (Including Distribution Losses)
– Voltage Required
– Operational Common Mode Voltage Range : ± 2.5 VDC
 Power Source Dependability
– Minimum Battery Voltage = 11 VDC
– Maximum Power Supply LEN Variation = 5%
Power Distribution:
Multiple Power Sources
 Split Power
– Compute Voltage Drop as for a Middle-powered
Backbone
 Isolated Power Supplies
– Each Power Supply Drives Backbone Segment;
Compute Voltage Drop for Each Supply as End or
Mid-powered
Power Distribution:
End-Powered Backbone Example
3 meters
Power is traveling right only
POWER
2 meters
6 meters
2 meters
5 meters
0.3 meters
Power Distribution:
End Power- Single Battery Example
NET-L
NET-H
NET-S
NET-C
Shield / Drain
Power Distribution:
Middle-Powered Backbone Example
2 meters
0.3 meters
0.3 meters
Power is traveling left & right
POWER
2 meters
6 meters
0.3 meters
0.3 meters
5 meters
2 meters
2 meters
Power Distribution:
Isolated DC Power Supply Example
NET-L
NET-H
NET-S
NET-C
Shield / Drain
Power Distribution:
AC Power Supply Example
NET-L
NET-H
NET-S
NET-C
Shield / Drain
Power Distribution:
Network Node Example (In Device)
CAN CONTROLLER
TRANCEIVER
I/O
 Isolation between Transceiver and CAN Controller
 Transceiver is Powered from Network Power
Power Distribution:
Dedicated Power Cable Routing
– NMEA 2000 Transceiver circuit is powered by the backbone
– Main power for LCD screen etc. is not powered by the
backbone
Device is more than 20 LEN
Dedicated power (separate from backbone)
Devices powered from backbone
Data & power for NMEA 2000
Transceiver ONLY
Drop Cable without power wires
(provided by manufacturer)
Power Distribution:
Larger Networks
 Multiple power T’s are needed when voltage
drop calculations exceed limits.
Power
Additional Power Tee
Only connected to the Right
Power Distribution:
Multiple Power Supplies
– Shield/drain wires (grey) are all tied together and only
bonded to RF grounding at one power insertion point
Power Distribution:
Larger Networks
 Heavy cable backbone
 Heavy Tees with Light / Mid drop connection
 Allows for drop cable to connect into all devices
Light cable drop connection
Voltage Drop Calculations:
Battery & Power Supply
Battery Powered Distribution Loss Budget
Minimum Battery Voltage
11.00 VDC
3% Loss at Insertion
- 0.33 VDC
Backbone Distribution Loss
- 1.17 VDC
Minimum Voltage at Device
9.50 VDC
Power Supply Powered Distribution Loss Budget
Nominal Power Supply Voltage
13.80 VDC
5% Output Variation
- 0.75 VDC
Backbone Distribution Loss
- 3.55 VDC
Minimum Voltage at Device
9.50 VDC
Voltage Drop Calculations:
Why Do We Need Them?
 Needed to ensure that all devices on the
network are getting adequate power.
 Devices furthest from the power insertion point
will get less voltage than the closest device.
 More than one power insertion point (Power
Tee(s)) may be needed to feed all devices.
 Voltage drop calculations help us determine this.
Voltage Drop Calculations:
Calculating the Voltage Drop
VOLTAGE DROP CALCULATION is Ohms Law;
E= I x R
E = Voltage Drop (VD)
I = Total Network LEN (NL)
R = Backbone Length (BL) in Meters (one way)
VD=.1 x NL x BL x Cable Resistance
– Cable Resistance Is in Ohms (Ω) per Meter
– Light Cable = .057 Ω
– Mid Cable = .015 Ω
– Heavy Cable = .012 Ω
Voltage Drop Calculations:
Example
Network LEN
Network Backbone Length
Cable Resistance-Light
Voltage Drop Estimate
13
14.3
.057 per meter
1.06 volts
E= I x R ( Ohms Law)
E = voltage drop (VD)
I = total network LEN (NL)
R = backbone length in meters (one way) (BL)
VD=.1 x NL x BL x .057
1.06= .1 x 13 x 14.3 x .057
Voltage Drop Calculations:
Calculator Keystrokes- EXAMPLE
 NL (LEN) = 7
 BL (Length) = 5.0
 Cable Type= Light (.057 Ω / m)
 Calculator Keystrokes are…
 .1 x 7 x 5 x .057 = 0.1995
 Round up at second decimal place → .20
Voltage Drop Calculations:
Calculator Keystrokes- EXAMPLE
 NL (LEN)=3
 BL (Length) = 4.2
 Cable Type= Light (.057 Ω / m)
 Calculator Keystrokes are…
 .1 x 3 x 4.2 x .057 = 0.07182
 Round up at second decimal place → 0.07
Voltage Drop Calculations:
Calculator Keystrokes- EXAMPLE
 NL (LEN)=12
 BL (Length) = 9.8
 Cable Type= Light (.057 Ω / m)
 Calculator Keystrokes are…
 .1 x 12 x 9.8 x .057 = 0.67032
 Round up at second decimal place → 0.67
Voltage Drop Calculations:
Calculator Keystrokes- EXAMPLE
 NL (LEN) =15
 BL (Length) = 20.3
 Cable Type= Heavy (.012 Ω /m)
 Calculator Keystrokes are…
 .1 x 15 x 20.3 x .012 = 0.3654
 Round up at second decimal place → 0.37
Voltage Drop Calculations:
Calculator Keystrokes- EXAMPLE
 NL (LEN)=19
 BL (Length) = 28
 Cable Type= Mid (.015 Ω / m)
 Calculator Keystrokes are…
 .1 x 19 x 28 x .015 = 0.798
 Round up at second decimal place → 0.79
Voltage Drop Calculations:
When Do We Calculate Segments?
 When VD exceeds 1.17 VDC using a ship
battery powered network
 When VD exceeds 3.55 VDC using a regulated
13.8 VDC power supply
Battery Powered Distribution Loss Budget
Power Supply Powered Distribution Loss Budget
Minimum Battery Voltage
11.00 VDC
Nominal Power Supply Voltage
13.80 VDC
3% Loss at Insertion
- 0.33 VDC
5% Output Variation
- 0.75 VDC
Backbone Distribution Loss
- 1.17 VDC
Backbone Distribution Loss
- 3.55 VDC
Minimum Voltage at Device
9.50 VDC
Minimum Voltage at Device
9.50 VDC
Voltage Drop Calculations:
Calculating the Segments
 Enter devices starting at the device closest to
the power insertion point.
 Enter segment lengths starting with the segment
between the power insertion point and the first
device.
 Always use the last drop length as part of the
total backbone length calculation
 Compute currents.
 Compute voltage drop in each segment for each
device.
 Add the voltage drops in the column.
Voltage Drop Calculations:
Segments on the Network
Calculate segments
left of power
Calculate segments
right of power
Voltage Drop Calculations:
Left Side of Power Tee
Voltage Drop Calculations:
Left Side of Power Tee
Voltage Drop Calculations:
Right Side of Power Tee
Voltage Drop Calculations:
Right Side of Power Tee
NEXT: Section 3
Connecting to Other Data Sources and Networks
&
Advanced Setup, Certification, Troubleshooting
Copyright © 2011 NMEA