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Old 26-11-2012, 01:17   #1
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Power Supply for N2K Network?

I have been reading, reading, reading on N2K network design, and I have taken a cut at my own planned network using the Maretron design software, which is extremely helpful.

One of the many things I'm still trying to figure out is the best way to do the power supply. I understand that N2K gear is designed to operate on a fairly wide range of voltage, and that the standard way to power the network is to basically inject 12v nominal power into it from the boat's DC system.

I bet, however, that the more stable the voltage is, the less risk of problems. Since I'm on 24v power I can't just inject power anyway.

Does it make sense to use some kind of stabilized power supply? I think that the Victron droppers (like this: http://www.victronenergy.com/upload/...3%20-%20EN.pdf) provide a stabilized output at an adjustable voltage, so you can provide the network with say 13 volts of power which will be steady even while the 24v nominal supply power fluctuates from 23.5v (dead batteries) to 30 volts (equalization charge going on) and everything in between.

Surely this would be a good thing -- what do you guys think?


Another thing I can't figure out is daisy-chaining. It is officially prohibited by the N2K standard, but if you have four or five instruments in the cockpit plus chart plotter plus pilot control head then you would have an incredible rats nest of drop lines to the backbone. Looks like most of the major manufacturers, like B&G (Simrad), allow their instruments to be daisy chained together exactly to avoid this situation.

What do you guys think about that?
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Old 26-11-2012, 02:42   #2
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Re: Power Supply for N2K Network?

DH,
I don't have any experience with NMEA2000 yet as my older stuff still meets my needs. They do have multi-port (4) junction boxes that should make your rats nest more manageable.
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Old 26-11-2012, 03:51   #3
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The more stable the power the better. Daisy chan g isn't supported by NMEA as taken to extremes it can violate bus timing. And some implementations compromise bus integrity. But in practice its fine.

Dave
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Old 26-11-2012, 05:17   #4
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Re: Power Supply for N2K Network?

I have worked a long time in the Truck Electronics Sector with J1939, NMEA 2000 is J1939.

Power from a battery is the most clean source you can find, all ECU's have an internal Voltage regulator. Don't worry.

What happens when you Daisy Chain a CanBus. (!!! with ECU's close together !!!) See Picture.

Nothing....
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Old 26-11-2012, 05:54   #5
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Re: Power Supply for N2K Network?

Daisy chaining could be an issue if one instrument up-chain died (or needed/desired to be turned off) and left the down-chain ones without power/signal? I could see wanting to turn off the chart plotter but still have the wind instrument work. Don't know if there is a pass-through design for this.

Multiport boxes are a great way to avoid multiple drops from a remote location.

Our B&G Tritons support daisy chaining and B&G installation instructions OK daisy chaining on the network backbone, but they specifically recommend against daisy chaining on a drop cable. However, they do not state any reason.

One tip: When designing a N2K network, one tries to place the power supply in the electrical mid point so that each side of the network uses equal power. However, this is really only necessary for very large networks full of instruments. I wired ours up this way, and the design put the power supply in the back of a drawer locker, where everything is neat and tidy.

However, I now realize that one advantage of N2K is that in areas of high lightning storms (like where we are now), one can simply unplug the power supply (and the drop cable from the mast, if applicable) and completely isolate the entire instrument system from the boat's electrical system. And hopefully have a better chance of working electronics should one take a strike or side flash.

So my (long) point here is to spend more consideration in placing the power supply in an easily accessible place than in a place that equally balances the system electrically. Most cruising boats would not have that much more electronics than we do, and I could power our network from a single end with no problems.

Mark
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Old 26-11-2012, 16:05   #6
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Quote:
Originally Posted by CeesH
I have worked a long time in the Truck Electronics Sector with J1939, NMEA 2000 is J1939.

Power from a battery is the most clean source you can find, all ECU's have an internal Voltage regulator. Don't worry.

What happens when you Daisy Chain a CanBus. (!!! with ECU's close together !!!) See Picture.

Nothing....
There is an issue with some of the architectures you describe. The propagation of the collision must occur within a fixed time window. Some of these architectures if taken to extremes and connected via long buses can exceed the collision propagation time.

Dave
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Old 26-11-2012, 16:08   #7
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Re: Power Supply for N2K Network?

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Originally Posted by goboatingnow View Post
There is an issue with some of the architectures you describe. The propagation of the collision must occur within a fixed time window. Some of these architectures if taken to extremes and connected via long buses can exceed the collision propagation time.

Dave
That's why I wrote;

What happens when you Daisy Chain a CanBus. (!!! with ECU's close together !!!) See Picture.

Nothing....
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Old 26-11-2012, 16:11   #8
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Quote:
Originally Posted by colemj
Daisy chaining could be an issue if one instrument up-chain died (or needed/desired to be turned off) and left the down-chain ones without power/signal? I could see wanting to turn off the chart plotter but still have the wind instrument work. Don't know if there is a pass-through design for this.

Multiport boxes are a great way to avoid multiple drops from a remote location.

Our B&G Tritons support daisy chaining and B&G installation instructions OK daisy chaining on the network backbone, but they specifically recommend against daisy chaining on a drop cable. However, they do not state any reason.

One tip: When designing a N2K network, one tries to place the power supply in the electrical mid point so that each side of the network uses equal power. However, this is really only necessary for very large networks full of instruments. I wired ours up this way, and the design put the power supply in the back of a drawer locker, where everything is neat and tidy.

However, I now realize that one advantage of N2K is that in areas of high lightning storms (like where we are now), one can simply unplug the power supply (and the drop cable from the mast, if applicable) and completely isolate the entire instrument system from the boat's electrical system. And hopefully have a better chance of working electronics should one take a strike or side flash.

So my (long) point here is to spend more consideration in placing the power supply in an easily accessible place than in a place that equally balances the system electrically. Most cruising boats would not have that much more electronics than we do, and I could power our network from a single end with no problems.

Mark
N2K systems that are daisy chained do not have active pass through, merely the bus connection point is inside the unit. Hence powering up or down the daisy chain device has no bus effect.

In my view ,larger n2k nets should be divided up into isolated bridged n2k sub nets ( all on the one collision domain) but this allows the primary high availability net to be isolated from say a secondary information only net.

Dave
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Old 26-11-2012, 16:17   #9
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Re: Power Supply for N2K Network?

Quote:
Originally Posted by goboatingnow View Post
N2K systems that are daisy chained do not have active pass through, merely the bus connection point is inside the unit. Hence powering up or down the daisy chain device has no bus effect.

In my view ,larger n2k nets should be divided up into isolated bridged n2k sub nets ( all on the one collision domain) but this allows the primary high availability net to be isolated from say a secondary information only net.

Dave
In simple words, the daisy chain connectors on an instrument (ECU) are internaly hard wired.

On a small boat, at the helm station, the ECU's are soo close together that Daisy Chaining them is absolute no problem.
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Old 26-11-2012, 16:21   #10
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Quote:
Originally Posted by CeesH

In simple words, the daisy chain connectors on an instrument (ECU) are internaly hard wired.

On a small boat, at the helm station, the ECU's are soo close togheter that Daisy Chaining them is absolute no problem.
Yes correct, which is why Furuno , and Raymarine and others can't pass full N2K certification as they do daisy chaining. NMEA takes the theoretical high moral ground, in practice it works.

In my view the whole N2K bus concept should be scrapped and replaced with hub/star and daisy chaining where useful. Much more reliable and fault tolerant. See any big yellow Ethernet busses around lately ..... ( remember them ) imagine in a big n2k network trying to find a short !!! ( which of courses takes the whole LAN out )

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Old 02-12-2012, 06:19   #11
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Re: Power Supply for N2K Network?

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Originally Posted by Dockhead View Post
...


Another thing I can't figure out is daisy-chaining. It is officially prohibited by the N2K standard, but if you have four or five instruments in the cockpit plus chart plotter plus pilot control head then you would have an incredible rats nest of drop lines to the backbone. ...
DH:

You can use on of these from Maretron.
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