Written by Ben Ellison on Apr 21, 2014 for Panbo, The Marine Electronics Hub
When Garmin recently introduced GNX20/21 displays, it led to questions about the power needs of similar but all-color NMEA 2000 instruments. And that led me to finally make up a special N2K cable that I can use with my trusty Power Analyzer Pro to measure the 12 volt current flow to an individual N2K-powered device. So what you're seeing above is that a Raymarine i70 working with live data at 100% brightness level is using 0.13 amps. That's not much by most standards, but dropping down a hair to 90% brightness reduced the power draw 20%...
I got into this testing, trying all the NMEA 2000 displays above at almost every brightness level they offer. The Maretron only has 3 brightness levels, the Garmin GMI20 is unique for 5% increments, and I took an educated stab at balancing the Furuno RD33's separate screen and keypad backlight (you only need help seeing the keys when the screen is quite dim). As you'll see in the results table below, all of the displays use significantly less power at slightly less than maximum brightness with power savings declining to almost zero as you dim them way down. I've seen similar results with large, individually-powered multifunction displays, though of course, the amperage saving increment is larger. It's great that marine screens have gotten so bright and readable, but if you're sailing or at anchor, it's power smart to keep displays turned down a notch or two. Interestingly, it made no power draw difference to invert colors -- all that bright white to black -- or to use red themed night colors.
What doesn't show in the table, though, is the huge difference between all the color screens and the Simrad IS20 representing monochrome technology. In my fairly well-lit lab, the color screens became unreadable somewhere below 50% brightness, but I could not detect the backlighting on the IS20 screen at all. In other words, a sailor can watch a monochrome screen all day for about 0.04 amps an hour, while a similar size color screen might need 90% brightness using twice the power. That's why Garmin came up with the GNX series, though for many boaters all those relatively low amperage readings are good news. Please note that this is not a definitive test of display efficiency; I don't have any way of measuring comparative screen brightness levels -- though they all look good -- and the power increments are so small that accuracy is dubious.
In fact, even the small scale Power Analyzer declines to measure tenths of a watt, which is why I used the amperage figures (while trying to keep the voltage steady at about 12.4). But as a testing bonus, I got to try the gray Posi-Twist wire connectors seen below. The Posi-Lock company also makes Posi-Tite waterproof inline connectors -- which were suggested when I revealed my infatuation with Scotch-Loks, especially for splicing thin wires -- but the Posi-Twist is more like a much-improved wire nut. They probably make the ABYC cringe, but I felt like that two-piece collar and cone design really clamped down on the twisted fine gauge wires (note that the packaging specifies use for 18-26 gauge, though the shop online listing says 20-24). They're much faster and easier to use on skinny wires than a conventional crimp and shrink connector, and with a dab of waterproof gel and some strain relief might hold up as long. I will definitely try the Posi-Tite connectors I also purchased.