Fuel for Thought
New APU - Part 2
In New APU Part 1, there were many things left to cover. So let’s get right into it.
I already described the tool box that houses my new GenMax 3500 generator and I showed you the venting I thought would be sufficient to keep everything inside cool. As this was my first such undertaking to DIY an APU, I overlooked one key aspect - venting only works when air is moving, that is, without air flowing through the vents it has very little effect. This is where the USB ports on the generator come into play. I had to go back to the venting, so I cut out another vent opening near the upper rear corner of the box, built a cover with some aluminum angle and added a louvered vent cover (but leaving the bottom open). I then installed two 5 volt fans across the inside of the new opening and these fans plug directly into one of the USB ports on the generator. Now when the generator is running, the fans are automatically powered on and everything stays cool inside the tool box and this eliminates heat and CO2 buildup inside the box.
Now to tackle the fuel issue. The generator has a 1.7 gallon gas tank. That is enough to run overnight (6 - 7 hours). As we all know, truck drivers usually need 10 hour breaks daily and often we are down for 34 hours to reset our hours for the week. So a larger fuel supply was needed. I opted for a spun aluminum fuel tank. These can be found in various sizes, however I settled on the 12.5 gallon size. Many drivers with catwalk generators will use a plastic marine tank and while I considered that option, my concern was the plastic deterioration over time causing leaks, so I opted for an aluminum tank which also mimics the trucks diesel fuel tanks to a degree (shape and material). This seemed more aesthetically pleasing as well as durable. If you consider the 12.5 gallon tank plus the 1.7 gallon tank on the generator, you can see that there will be fewer trips to fill up. You can definitely get through the hottest or coldest 34 hour restarts without running out of fuel.
Please note that any modifications done to a generator will most likely void the warranty, but I was willing to take that risk. However, the only modification I had to do was the gas cap.
In order to connect the new fuel tank to the generator, some fabrication work was needed. First I ordered a spare fuel cap and then bought all the various fittings and hoses needed. A marine fuel line with a primer bulb, fuel line, shut off valve, various hose barb fittings and pipe sealant designed for fuel connections. After gathering the supplies it was just making the connections. I used all ¼” fuel hose and fittings since the tank has a ¼” port. The shut off valve is installed on the fuel tank, fuel line routed (use wire loom or techflex to protect the hose) and secured to an opening in the rear of the tool box (use a grommet to prevent chafing and cuts), inline fuel filter and the connection to the fuel cap. For this, just drill the appropriate size hole in the top center of the spare fuel cap. Attach a male and female hose bibb fitting (with sealant) through the cap, Attach a short length of fuel line to the bibb inside the cap. The fuel line inside the cap must reach and remain in the fuel inside the tank to continue to siphon from the external tank. Use the primer bulb to start the flow of gas from one tank to the other. Whatever tank you decide to use, make sure it is vented. A plastic unvented tank will suck in the sides as it empties since it does not allow air to replace the space now devoid of fuel. The aluminum tank I am using has a vented cap. If you wonder why I used a spare fuel cap rather than modifying the original, since the generator is portable, I can easily change the fuel caps, remove the generator and use it for other needs. It will also come in handy to use the original cap when removing the unit to change the oil, spark plug or air filter cleanings.
Okay, this got a little long as did the first, next time when we will talk about wiring options since it did not make into this one and maybe get to some of the unforeseen benefits of this type of APU.
Visualize this thing that you want, see it, feel it, believe in it. Make your mental blueprint, and begin to build.
- Robert Collier
See you down the road,
Greg