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Using Network Cable To Replace Serial Cables

PhatRV

Well Known Member
I was thinking about the serial network cables in the modern Dynon avionic network communication. The Dynon uses 9 wires to transfer serial data from each of the avionics component to the main HDX display. With the exception of the EMS - HDX connection, all the serial wires only require 8 wires or 4 twisted pairs. In the CAT6 cable, the wires are already constructed with 8 twisted pairs using 23 AWG wires, slightly less than the standard 22AWG aviation wire.

With that information, what is the downside of using the CAT6 cable to connect the various avionics together, making the wiring run less cumbersome? Of course there has to be a Network - DB9 connection board for the final connection to the HDX display but I am thinking of running network cable is a better solution than rolling your own and making the connections much more reliable. In the DB9, every wire has to be individually crimped and inserted in the correct pin number. In the network cable connection, the crimper does the job and from the billions of network connections, I don't know of a failure yet. Having spending may hours with my own Dynon DB9 connections, I have caught a few mistake while checking the work.

Aside from the network cable not "aviation" grade, most of the avionic wiring are located in the benign environment of the fuselage and avionic bay, not in the hot engine compartment.

Any opinion? I know commercial airplanes use shield network cables for the obvious reason due to the certification at that level of safety regulation. There is no shielding needed in our small airplane so CAT6 cable should work in our application.
 
With that information, what is the downside of using the CAT6 cable to connect the various avionics together, making the wiring run less cumbersome? Of course there has to be a Network - DB9 connection board for the final connection to the HDX display but I am thinking of running network cable is a better solution than rolling your own and making the connections much more reliable. In the DB9, every wire has to be individually crimped and inserted in the correct pin number. In the network cable connection, the crimper does the job and from the billions of network connections, I don't know of a failure yet. Having spending may hours with my own Dynon DB9 connections, I have caught a few mistake while checking the work.

Aside from the network cable not "aviation" grade, most of the avionic wiring are located in the benign environment of the fuselage and avionic bay, not in the hot engine compartment.
My question would be, what is the upside? Is CAT6 and connectors from Radio Shack going to be in any way better than an already-proven SV network?
 
I think you will make the install more complex and add more points of failure. How will you terminate the rj45 to the db connectors? The ethernet cables typically have a smaller gauge wire, which may not make them a good candidate in you plane. Terminating the pins in with a db connector is a whole lot easier than with with rj45 in my opinion.

Also remember that any modification that doesn’t comply with existing standards could have the potential of impacting resale value.
 
Actually, only 4 of the wires in the Dynon DB-9 connector are for data, the other five are power and grounds. Dynon recommends twisted pairs for the PWR1/GND1 and PWR2/GND2 connections as well. A single run ninth wire is the EMS Aux power. You could use Tefzel wire and twist the pairs yourself for the recommended 8-10 twists per foot.

I would not recommend using RJ-45 connectors. First, you are one wire short of the 9 required and second you are passing power on half the contacts. Dynon did not list the current for the power wires, current limit for DB-9 is 3 A per pin and RJ-45 is 1.5A. I have some DB-9 to RJ-45 RS-232 wire converters in the electronics shop and would never use them in the aircraft.

You could get by with Plenum rated CAT6 cable (23ga stranded), but I would still use crimped machined pin DB-9s.

John Salak
RV-12 N896HS
 
I've been making the network cables lately for my Dynon Skyview system in my RV-3B. I've found that it's not at all difficult, and checking is also easy. I verify every wire after installation.

Dave
 
I finished all of my Dynon avionics with self-made twisted wires and DB9 connectors but all the while, in the back of my head, I thought there has to be a better process.

From the Dynon tech manual, the max current for the devices on the network is 0.15A (ADHARS) which is miniscule so the 23AWG gauge wire can handle the load.

The picture below is the from the Dynon system running 12V. The 1.0A is for the backup battery but it has a dedicated wire instead of connecting to the network. So from the electrical specification, there is plenty of margin with the CAT6 cable.

From the resale perspective, a buyer switching from flying a C172 probably doesn't mind, even the wow factor of seeing the network cables. Much like in the early 2000 when all the Vans RV had the glass panels for the first time. Nothing was tested but we installed them as guinea pigs. They do get a lot of look from the certified crowd
 

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