Diagnosing power issues on your NMEA 2000 network with Smart Terminators

Issues with NMEA 2000 networks often occur simply because the bus is not powered or the voltage is too low. The TER-U is an intelligent NMEA 2000 terminator, which can be used as Male, Female or In-line, simply by moving the blanking cap at the end. The product contains internal LEDs which illuminate depending on the voltage level being measured, thanks to the high-accuracy monitoring circuit contained within the TER-U. 

Detecting voltage issues

A common issue that we see on larger and more complex installations is the voltage across the network starts to drop below the recommended threshold. NMEA 2000 devices operate on 9-16VDC, where a minimum of 9V is required to power the device (or at least the CAN Transceiver if an independent supply is used). When the network voltage drops below 9V, devices start to operate incorrectly, power cycling, outputting invalid data, losing and reclaiming their source address etc…  

The power drops more the further we get away from the power supply, so the devices that are connected nearer the extremities of the backbone (closer to the terminators) are the ones more susceptible to power supply problems. This is where the TER-U comes in, with the internal LEDs;  

The LED will illuminate ‘GREEN’ if the network voltage is at 9V or more, or it will be ‘RED’ if under 9V (it can also be off which shows it’s under 4.5V meaning the polarity of the power supply is incorrect). A simple visual check with a TER-U allows for a quick indication of the network voltages. If the device at one end of the backbone is constantly disconnecting, and the TER-U next to it is showing as ‘RED’, then we know that there’s a fundamental problem with backbone power at this end. If the LED is ‘GREEN’, then we know that the voltage is good, and there is another issue causing the device to misbehave.

The aim of this is to save the installer, technician or end user time and money when investigating any issues. Instead of connecting to a T-piece at the end of a network and then touching a multimeter over the CAN-S and CAN-C wires off a spliced drop cable, we can just look at the TER-U LED.

Universal terminator

The other advantage of the TER-U is that it can be used as an in-line or ‘feed through’ terminator, ideal for the installation of devices and networks that run up masts. On sailing boats, it’s not uncommon for the backbone to need to run up the mast for wind instruments to be connected. Of course, up a mast, there is very limited space for things to be installed, and trying to get a backbone, t-piece, drop cable, instrument and terminator up there can sometimes be impossible.  

Using an inline terminator overcomes this challenge, as we can put the inline terminator on the backbone, just before the last device, and the network will still behave as expected. Provided the terminator is correctly installed and the wind instrument is kept within 6m with no other drop cables or devices connected off of this, the topology doesn’t change.