NMEA 2000 Question

Habebty

Habebty

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I bought a new Garmin chart plotter to display AIS targets from a Vesper XB8000. I thought I would start an N2k network to eventually attach new log and sounder as well.
All the online research I looked at suggested all I had to do was create a backbone and drops to each piece of kit, as power and data are in the one cable.
So that’s what I did and nothing worked. Both the Vesper manual and Garmin showed no need to connect a separate power supply. In fact the Garmin manual even said “do not connect a separate power supply” to the plotter.
Talked to a couple of people, and they all said “no, you need a separate power supply”
So reconnected the separate power feeds and everything worked, with AIS targets showing on the plotter.

So my question is, just what are the power supply capabilities of N2k, will the backbone and drops, power log and sounder displays and transducers etc.

Thanks
 
NMEA2000 will deliver power, I believe, but looking at the thin wires used for the NMEA connection on my XB8000, you would not be able to deliver much power over much of a distance. Perhaps you could use a backbone with much thicker multicore cable to be able to deliver enough current?

Richard
 
The N2k backbone needs its own power supply. Some low power devices such as wind speed sensors or temperature sensors will take their power from the backbone. More power hungry devices such as plotters, AIS units, sounders will need their own power supply as well. If the device comes with a power supply lead then connect it up. If it doesn’t have separate power connections then you can assume it will be powered by the N2k bus. There is a limit to how much power the N2k bus can provide and in larger setups you need to split the bus and provide 2 power connections.
 
Yes, thanks for all the above, it just seemed strange that in all the schematics on websites, and YouTube installation videos I looked at, none mentioned the power capabilities of N2k cables. They did mention the need for additional power feeds into the backbone to allow for voltage drop in long networks, but not what devices can and can’t be powered by N2k.
Is the “len” number a clue?
 
LEN is the load equivalent number. The backbone can, I think, according to spec provide up to 4 LEN before you need to look at other power sources. In reality I've never had an issue or worried about it too much.
 
Keith-i said:
LEN is the load equivalent number. The backbone can, I think, according to spec provide up to 4 LEN before you need to look at other power sources. In reality I've never had an issue or worried about it too much.
Click to expand...

4LEN is way too low, maybe 20 or more?
I have at least 12LEN plus 4 custom arduino boxes taking power from the bus and all's working fine.
I'd say a rule of thumb is that any black box and any display less than 5 inch is powered from the bus. Obviously plotters/radars/sounders/VHF excluded!

V.
 
vas said:
4LEN is way too low, maybe 20 or more?
I have at least 12LEN plus 4 custom arduino boxes taking power from the bus and all's working fine.
I'd say a rule of thumb is that any black box and any display less than 5 inch is powered from the bus. Obviously plotters/radars/sounders/VHF excluded!

V.
Click to expand...

One LEN = 50mA, max network load is 3a, so 60 LEN
 
So a plotter with a LEN of 1 and a Vesper AIS with a LEN of 2 should be able to take power from the network without the need for their own independent power supply? Yet won’t work without a separate power supply to each device.
Sorry if I’m missing something, but although what I’ve installed seems to be working, I like to know how or when it’s going to blow up :)
 
Habebty said:
So a plotter with a LEN of 1 and a Vesper AIS with a LEN of 2 should be able to take power from the network without the need for their own independent power supply? Yet won’t work without a separate power supply to each device.
Sorry if I’m missing something, but although what I’ve installed seems to be working, I like to know how or when it’s going to blow up :)
Click to expand...

No. If your plotter has a LEN of 1, that's 50mA, that's not enough power to run a plotter, you'll need at least an amp for that. LEN refers to network load, not the power required to run the plotter.

Your plotter will need a power supply to run, whether or not it is connected to a NMEA 2000 network. If you connect it to the network, it will impose a 50mA load on the network. Same goes for the AIS.

Some very, very low power devices, small displays typically, use such a small amount of power they can take it from the network, these generally have a higher LEN than your plotter.
 
PaulRainbow said:
No. If your plotter has a LEN of 1, that's 50mA, that's not enough power to run a plotter, you'll need at least an amp for that. LEN refers to network load, not the power required to run the plotter.

Your plotter will need a power supply to run, whether or not it is connected to a NMEA 2000 network. If you connect it to the network, it will impose a 50mA load on the network. Same goes for the AIS.

Some very, very low power devices, small displays typically, use such a small amount of power they can take it from the network, these generally have a higher LEN than your plotter.
Click to expand...

Thanks Paul, that clearly answers my question.
 
sorry, but plotter has a LEN1 and AIS LEN2 BECAUSE they NEED separate power supply to function so they don't "waste" energy/hog the bus!
cannot really have a GPS polling and a large screen backlight with minimal power consumption...
OTOH, a N2K thruhull, a 4in multidisplay, a GPS antenna, a wind instrument etc consume minimum power and take their power from the bus

V.

PS. sorry guys, didn't read all the messages before replying...
 
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