LED Light for Fuel Gauge
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| Fuel gauge lit by LED light |
Over twenty years, the tube gradually turned to a dark brown that made it hard to read the fuel level, particularly in bright sunshine.
The discoloration problem was easily solved with installation of a new tube. But it still was difficult to read the fuel level; it seemed harder than I recalled from years ago, when the tube was still clear. This was likely due to the fact that autogas is no longer colored the way it used to be, when brands wanted to differentiate themselves. In fact, gasoline has become a truly generic product, with refineries swapping fuels any which way to reduce distribution costs.
Something new was needed. Enter LEDs: Cheap, low power consumption, available in various shapes and sizes, as individual lights or in strips. Our display problem called for experimentation with that technology.
Searching on the Internet, we found a super bright LED, white, 5mm diameter, 9-16V, 5W. Ten LEDs for less than $10, including shipping. We bought several since experimentation might damage some of them. Indeed, we ruined one during that process.
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| Super bright LEDs: 5mm dia, 9-16V, 5W |
The first idea was mounting one LED behind the panel to illuminate the nylon tubing. This wasn't a good idea: One could see the light very well, but the fuel level wasn't clearly shown. More trials, moving the LED around.
Eventually, a surprising solution: the light mounted in front of the panel at the bottom of the nylon tube. The nylon absorbs much of the light, channels it upward inside the tubing and fuel. The light is refracted when the fuel level is reached; see above photo, where about 6.7 gal of fuel are indicated by a bright horizontal line inside the tube.
We mounted the LED using a small aluminum bracket, with surface toward the light bulb painted white. The LED is moved far enough downward into the bracket so that it cannot be seen even when the pilot bends forward.
A general complaint posted on the Internet about LED lights says that the wires are flimsy. The word does not begin to describe the small size and fragility of the wires. Even with a first-rate stripper, it was difficult to remove the insulation without damaging the stranded wire. But with some effort, we succeeded.
For the installation, we soldered 22-gauge aircraft wire pieces to the flimsy wires and covered the connection with heat shrink tubing. The aircraft wires were then connected to the panel.
There was more to consider. Our plane no longer has a mechanical fuel pump and runs solely on an electric facet pump with automatic backup by a second facet pump. In case the alternator fails, all nonessential power users are turned off. That had to include the LED light. So we wired the LED light to the switch that powers the two gyros, since they definitely will be turned off if the alternator fails.
Another consideration is the heat dissipated by the LED light bulb. Yes, it is just 5W, but that still produces some heat that we would not want near the nylon tube. So the light bulb is mounted against the aluminum panel, and any heat is absorbed by the panel.
In the final test of the installation, we pointed a bright LED flashlight and a trouble light, in bright daylight, at the panel. But regardless of the position of these lights, the nylon tube remained brightly lit by the single LED, and the fuel level could be clearly seen. What an improvement after years of squinting at the fuel gauge, trying to make out the fuel level!
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