More specifically, I caution against the Amphenol LTW Field Installable connectors seen at bottom above, and I hope the photo illustrates why. Top to Bottom: Maretron, Actisense and LTW field fit N2K connectors However, the QPD has been discontinued, although there are many still in the supply chain and this is not the sort of product where you have worry about updates.īut how about that simple yet fully split A2K-MPT-1 Micro Power T-Piece? It will certainly get the job done, but also leads to an extra subtle N2K gender issue. Meanwhile, the two QPD Quick Power Drop models, which I discussed in 2012 along with other N2K network details, offer dual power entries and split feeds along with other QNB goodies like reverse polarity and data activity LEDs, as shown in the Actisense Power Feed Guide (PDF) seen in part above. It’s subtle indeed, but possibly important to someone who wants to keep part of an N2K network constantly alive on a meager power budget.
NMEA 2000 NETWORK DESIGN SOFTWARE PLUS
You can feed the internal power terminal block with a heavy gauge wire fused at 8 or more amps, and each side of the network will get 4 amps to supply each device N2K processor plus any N2K-powered sensors, but you can not switch the sides separately. So as rugged and flexible as the Actisense QNB is - note the choice of gland or Micro C port models, or you can mix your own with A2K-PMW connectors - it does not have separate power feeds. And it will meet the NMEA 2000 standard fine as long as the five added drops are not more than 5.5m long, as I’ll illustrate. All 8 ports are female, which is what you want gender-wise as N2K device ports are always male (aka pins showing). (Note that the latter multi is well made by Turck, and if you’re thrifty and adventurous note that I’ve found inexpensive yet industrial strength Turck 8-way multi-ports on eBay that are still working well on Gizmo).īut you can also use regular tee connectors to share a drop, so what you see above is an 8-port N2K network based on the Actisense all-in-one’s very short backbone but extended with a 0.5m Maretron cable and an Actisense A2K-4WT usually used along a trunk line. The 6m (20ft) maximum drop length can be branched in various ways and there are multi-ports specifically designed for the purpose, like Actisense’s own A2K-4WD NMEA 2000 4-Way Instrument Drop or Maretron’s Micro Multi Port. Moreover, a drop (also known as a spur) from an N2K backbone (aka trunk) can be much more than one cable to one device. Legal N2K network with 8 female ports and a 4-tee backbone That’s a big network, and I’m told that the NMEA was conservative in terms of what other standards permit on the same DeviceNet Micro C “physical layer” (also known as cabling and connectors). (And please ignore the wire nuts, which should never be seen on a boat.)īut for Micro cable networks the NMEA permits up to 50 devices on a backbone up to 100 meters (328 feet) long with numerous drop cables up to 6m (20ft) long (but not exceeding 78 m or 256 ft in total drop length). Secondarily, there can’t be much voltage drop as the 12v DC passes from the power drop cable out to the far ends of the network. The terminating resistors, for instance, are from different manufacturers (though they should provide the same resistance), and I think that skinny power drop cable may contain power wires even smaller gauge that the 22 AWG that’s normal with the N2K Micro size cabling most boats use.Īs I understand it, the main characteristic of a reliable N2K cabling and connector design is clean impedance in the data wires, which means good connectors throughout and proper backbone termination. I don’t actually remember when or why I put together this funky 3-way backbone and power drop, but I know it works OK while also illustrating numerous poor practices. Funky DIY 3-way N2K network with backbone to growīut let’s start with what you can get away with… at least with a small NMEA 2000 network… and at least most of the time.
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