NMEA-2000 Network Terminators

Electrical and electronic topics for small boats
porthole
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NMEA-2000 Network Terminators

Postby porthole » Fri Apr 08, 2016 10:05 am

If I use two 4-port T-connectors, I will have one extra open port. Can I just add an additional terminator to the extra port, having a total of three terminators on the backbone?

Or is the terminator limited to just two?

[Backstory below]

Currently I have one 4-port (Lowrance) Tee (which actually has six ports) and three single Tee (which have three ports) connected to the 4-port by a two-foot cable.

4-port Tee has:
--B+ supply to backbone
--HDS Gen3 #1
--HDS Gen3 #2
--OUTBOARD PILOT

The three single T-connectors have
--Fluid Level sensor (fuel tank)
--Fuel flow sensor
--Point 1 sensor

The 4-port-T connector is compact. Three 1-port-T connectors take up more room.
Thanks,
Duane
1999 Outrage 21
1999 Yamaha SW Series II 200

conch
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Location: Florida Keys,Hawaii,Mississippi

Re: NMEA-2000 Networks

Postby conch » Sat Apr 09, 2016 9:55 am

This is from some Lowrance NMEA-2000 General Information:

NOTE:
If you have a double -T-connector on your network that is not attached to a device, you must cap the unused connector with a NMEA 2000 cap. This will protect the pin connectors from corrosion. The NMEA 2000 cap looks like a terminator, but has "Cap" into the connector housing.

In order for the network to operate, you need 60-ohms of resistance to pull the network back to its recessive state after a signal is sent, so the next pulse can be heard. Two 120-ohm terminators in parallel are used to create this resistance. Attach a 120 ohm terminator to one end of the NMEA 2000 backbone. Attach the second terminator to the other end of the backbone.

NOTE:
NEVER attach a terminator to a NMEA 2000 network bus that has already been terminated.

jimh
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Re: NMEA-2000 Network Terminators

Postby jimh » Sat Apr 09, 2016 9:57 am

A NMEA-2000 network should have only two terminators, one at each end of the physical backbone wiring. The terminator provides a resistive load to properly terminate the network wiring which is acting like a transmission line. The terminator suppresses the tendency for the electrical signals on the line to be reflected back from unterminated cable endings.

Adding a third terminator to network backbone wiring is improper, and it may (or probably will) affect the electrical operation of the network.

There is no harm to network operation in having one port of a 4-port T-connector not connected to a device. Do not use a terminator to cover this open port. Do not leave an used extension cable connected here, either. To protect the open port from the weather, use one of the colored flexible vinyl caps that came on your Lowrance HDS when it was shipped that covered the connectors on the rear panel, or use some fresh 3M Scotch Super 33+ vinyl electrical tape to cover the sockets on the unused connector on the 4-port T-connector.

lowranceConnectorCap.png
Lowrance soft vinyl connector caps
lowranceConnectorCap.png (14.52 KiB) Viewed 4483 times


I have never seen a cap as described above in the quoted material from Lowrance, or any place to buy one. Although the quoted material is attributed to Lowrance, I believe it comes from an older version of the their literature, and I have some doubt that they are still providing such a device for retail sale.

conch
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Re: NMEA-2000 Network Terminators

Postby conch » Sat Apr 09, 2016 10:21 am

Star Marine Depot lists Maretron NMEA-2000 connector caps. Part # M000101 Female and Part# M000102 Male at their online store.

jimh
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Re: NMEA-2000 Network Terminators

Postby jimh » Sat Apr 09, 2016 10:49 am

Yes, I suspect MARETRON may have these caps. Perhaps you can give the URL to where you buy them. It would be much handier that way. I think you may have been talking about these:

http://www.starmarinedepot.com/maretron ... ector.html

For $3 for a cap and then $11 for ground for shipping, I'll look around for the free vinyl cap that came with the HDS. I never throw anything away.

You can also get Micro-C Connector Caps from other sources, such as Molex--who is probably the OEM of a lot of these cables---although I have no idea where you'd actually find a Molex distributor with them in stock:

http://www.molex.com/molex/products/dat ... Lang=en-US

conch
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Re: NMEA-2000 Network Terminators

Postby conch » Sat Apr 09, 2016 11:16 am

Yes that shipping would be high. Probably best to include them with the initial purchase of a 4 port T. They are also on E-Bay with free shipping.

I would prefer a threaded cap to using tape on a port. as access to half my T's are in a closed overhead electronics box with flush mounted MFD's ,VHF, and spotlight controls and, once buttoned up, I hope to not have to get in there again for quite some time.

conch
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Re: NMEA-2000 Network Terminators

Postby conch » Sat Apr 09, 2016 11:50 am

Actually Duane, since this is for your boat, why not add a Lowrance Link 8 radio and fill that NMEA-2000 network backbone port. Problem solved.
Chuck

porthole
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Re: NMEA-2000 Network Terminators

Postby porthole » Sat Apr 09, 2016 6:24 pm

So I learned three things that apparently were not in my manuals or were not clear in my manuals and installations instructions:

--only two terminators are needed, but there must be two,

--they should be at the ends of the network backbone, and

--a plain cap can be used on the empty port.

Currently [my network] is not [wired] like that. On one end of the four-way tee I have the [network power].
Thanks,
Duane
1999 Outrage 21
1999 Yamaha SW Series II 200

porthole
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Re: NMEA-2000 Network Terminators

Postby porthole » Sat Apr 09, 2016 6:26 pm

conch wrote:Actually Duane, since this is for your boat, why not add a Lowrance Link 8 radio and fill that NMEA-2000 network backbone port. Problem solved.
Chuck


That did cross my mind, if I do change radios though I will be leaning toward a second GX-2200.

I contacted Standard Horizon and they have no plans for a NMEA-2000 radio.
Thanks,
Duane
1999 Outrage 21
1999 Yamaha SW Series II 200

jimh
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Re: NMEA-2000 Network Terminators

Postby jimh » Sat Apr 09, 2016 6:54 pm

porthole wrote:...I contacted Standard Horizon and they have no plans for a NMEA-2000 radio.


You got the official company answer about new products not yet announced. Until a company formally announces a new product, that product officially does not exist.

jimh
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Re: NMEA-2000 Network Terminators

Postby jimh » Sat Apr 09, 2016 6:59 pm

porthole wrote:So I learned three things that apparently weren't in or not clear in my manuals and installations instructions:

--only two terminators are needed...


Not quite. A small network with a very short backbone length can be constructed with a star configuration with all branches meeting in common at a central point, and one 60-Ohm termination is used at the common point. It's a network whose backbone length is zero and all the cables are drop cables, with none more than 20-feet in length.

CaptRon
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Re: NMEA-2000 Network Terminators

Postby CaptRon » Sun Dec 30, 2018 2:28 pm

jimh wrote:Not quite. A small network with a very short backbone length can be constructed with a star configuration with all branches meeting in common at a central point, and one 60-Ohm termination is used at the common point. It's a network whose backbone length is zero and all the cables are drop cables, with none more than 20-feet in length.


Could I use a single 60-Ohm terminator, some wire and two Micro-C pin connectors to make a short NMEA 2000 cable to connect a [VHF] radio and chartplotter together? Both are located less than two feet apart. Similar to a RS232 crossover cable. Less expensive than a "Starter Kit".

jimh
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Re: NMEA-2000 Network Terminators

Postby jimh » Mon Dec 31, 2018 1:50 pm

Ron wrote:Could I use a single 60 ohm terminator, some wire and two Micro C pin connectors to make a short NMEA 2000 cable to connect a VHF radio and chartplotter together? Both are located less than two feet apart. Similar to a RS232 crossover cable. Less expensive than a "Starter Kit".


Your plan fails because you did not provide power to the network. Also, you do not make a "crossover" cable, as the network bus is bidirectional. Also you need connectors with sockets, not pins. But other than those problems, yes you could make a kludge.

If you know for certain that you will never have more than these two devices, you could construct a network as follows:

  1. buy an unusual cable with female Micro-C connectors on both ends; I don't know where you'd get one;
  2. buy that unusual cable with enough length to reach between the devices and have some slack to work with;
  3. in the center of the cable, very carefully remove the insulation to reveal the four insulated conductors and the bare drain shield wire;
  4. locate the two power wires; usually you can identify them by their insulation color; there are standard colors for the wiring in NMEA-2000; see the standard for advice; be careful to check because the cable you get might use non-standard wire colors
  5. wire a two-conductor cable with red (positive lead) and black (negative lead) conductors to the two power conductors, observing proper polarity;
  6. insert a 3-Ampere fuse in the red lead, or connect to a fused power distribution circuit with a 3-Ampere fuse in the distribution;
  7. connect to a source of 12-Volt power that can be controlled by a switch; you won't want the circuit to be live all the time;
  8. locate the two data conductors; usually you can identify them by their insulation color; again, be careful about color codes and standards;
  9. wire a 60-Ohm non-inductive 1-Watt resistor across the data pair;
  10. make all of these connections well insulated and waterproof, perhaps by installing them in a sealed enclosure.

If this sounds better than buying a pre-made set of network cables, T-connectors, terminators, and a power insertion node, then you will be in business, until you decide to add another node. They you can throw out that mess and buy the starter kit.

Typically about five minutes after you make your two-device network, you will get a third device that wants to connect to it, too.

Also the price of individual cables is rather high. Starter kits are good values.

jimh
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Re: NMEA-2000 Network Terminators

Postby jimh » Mon Dec 31, 2018 1:57 pm

For advice on good values in NMEA-2000 starter kits, see my earlier article on that topic at

viewtopic.php?f=9&t=344&p=2318#p2318

I also like this small boat network device; it retails at $80 and makes a very neat installation:

https://www.starmarinedepot.com/actisen ... k-kit.html