I'm about the light this candle with a G3X installation, and I'm a bit confused about CANBUS wiring. I see notes in the install manual diagrams about CANBUS wiring not to exceed 1M - what's that all about?
Also, in my RV-8, I have just installed Whelen Orion 600 nav/strobes and LED landing lights, which do not *require* shielded cable, but I used it anyway. The cabling runs inside the wing conduit, and I plan to use the conduit to run the cabling to the roll servo. Will this be a problem? BTW, the Orion nav/strobe and the LED landing lights replaced an old, noisy Whelen nav/strobe xenon and H3 landing lights.... The new setup is absolutely radio/intercom silent.
Hello maus92,
Good questions.
The 1 meter maximum length specified for the CAN node length has some theoretical value, but it has little value in the real world for those of us wiring airplanes.
As described above and in many other postings on VAF, the shielded pair CAN bus should be daisy-chained from one device to the next throughout the plane, keeping the wires going from the main CAN bus to the device connector (the node) as short as practical - which generally means a couple of inches.
The real guidance on node length is in the first paragraph of section 2.3.1.3 which states "keeping the node length as short as practical is recommended".
We will probably be removing that 1 meter guidance from the installation manual since it seems to add more confusion than value.
There is no length limitation between devices on the CAN bus that are daisy chained together, and some customers try to interpret the 1 meter node limitation as applying to distance between devices, which isn't accurate.
We have seen some large harnesses that had a CAN backbone up to 70 ft long and this is no problem when the CAN bus is daisy chained to each device and properly shielded and terminated (at each end).
You can get into trouble if you turn the CAN bus into a "star" network by connecting several devices to the same general section of the main CAN bus (such as with a hub), so we always tell builders to ignore the 1 meter limitation, and just daisy chain the CAN bus to each and every device in a serial fashion throughout the plane and you will be fine.
As stated in the previous post, we prefer to keep the CAN high speed data bus from sharing a wiring conduit or wiring bundle with strobe wiring, but you are welcome to give it a try.
We have built-in diagnostics that displays the CAN error rate from PFD1 to each device on the CAN bus, so you could test turning on/off the strobes and see if there is any measurable impact should you decide to share that conduit. Except during power up/down of devices on the CAN bus, any error rate that exceeds 0% is considered unacceptable. CAN bus data errors will be non-existent in a good installation.
Thanks for choosing G3X!
Steve