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Dirt Cheap Onboard Air Supply

Posted in How To: Electrical on January 12, 2017
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Call us cheap. No, seriously, call us cheap! We take pride in our frugality. It’s true that the homemade toilet paper didn’t work out the way we hoped it would, but all of our ideas can’t be winners. This time, we’re tackling an on-board air supply system, so at least it’s not a hygiene issue.

Few things increase your rig’s off-road prowess more effectively than airing down the tires. It helps increase traction and can smooth out washboard roads. The only problem with airing down is, unless you’re wheeling a trailer queen, you have to air back up at that end of the day! There are plenty of compact portable air pumps available that plug into a cigarette lighter or clamp to a battery for power. They can be a little slow, but they’ll get the job done. However, what if you need the sort of air pressure to run an impact wrench or get tire bead back on a rim? There are several companies that make complete on-board air systems, but they’re not cheap.

The heart and soul of our homespun onboard air setup is the Tsunami MF-1050. These little beauties put out 2 cfm each at up to 120 psi, and one of can inflate a flat 33-inch tire in about two minutes. We’ve used this compressor in several vehicles, and they’ve proven themselves to be cost effective, durable, and reliable. For our homebrewed onboard air setup we also picked up a heavy-duty relay to run everything through. The relay is normally used as a starter solenoid in Ford pickups, so it will easily handle the 60 amps our pair of compressors can potentially draw.

We began playing with the Tsunami MF-1050 air compressor, but it seemed to struggle with filling up a 5-gallon Port-A-Air tank within its duty cycle. The simple solution was to add a second Tsunami MF-1050. The cool thing about making your own compressor setup is that it gives you the flexibility to scale up or down based on your needs. If you’re only filling tires you may not need a 5-gallon tank or two compressors, but if you wanting to run air tools, you could swap in a different manifold to get the desired cubic-foot-minute (CFM) air output. This is by no means what everyone needs, but it’s an option we feel will fill (pun intended) our needs. Check out how we did it.

At only 7 inches tall, the compressors (the first shown mounted in this photo) were easy to mount just about anywhere. We decided to place them under the driver seat. The manifold used on the tank had three ports: two for the compressors and one for the output. The reason for the dual compressor setup was for faster fill and recovery times if needed. The only place we wouldn’t recommend installing them would be in your engine bay, as the compressors are air-cooled and the under-hood heat could limit their duty cycle.
Just because a big-name company stamps their name on the side of an air tank doesn’t mean it’s worth its weight in gold. Harbor Freight sells a 5-gallon portable air tank for less than a quarter what some of the major companies are charging for their tanks.
True, our tank was a bargain, but sometimes saving a buck means you have to make some compromises. In this case, the portable air tank was designed to be filled with a standard air chuck, not an attached compressor, which means we only had one 1/4" NPT and 1/8” threaded bungs for the compressor and pressure cut-off switch. The solution was as simple as running to our local hardware store for these T-fittings.
The pressure cut off switch is set so that the compressor shuts off at 120 psi and starts back up at 90 psi. With what this system costs you’re not going to be able to run an impact all day long but with the system fully charged you can easily zip a tire off which is exactly what we needed.
OK, we are guilty of this and have learned the hard way. Whenever you’re passing wire through the firewall, or any bulkhead for that matter, do yourself a favor: run down to Harbor Freight and spend the $5.99 on the company’s rubber grommet set! When you think about it, this is cheap insurance because if you just run wire through a hole you drilled, that sharp edge will over time rub through the insulation on the wire causing a short and potentially a fire.
Where you put the relay is only limited by space and how much wire you have. We’re cheap, and the heavy gauge wire you use between the battery and relay can be pricy, so we like to keep it near the battery so we can get away with using a shorter length of wire.
The tank is a little harder to hide in smaller jeeps like our flattie, but newer CJs and up have enough room behind the back seat to easily fit the tank and even the compressor if you don’t like it rattling under your seat. With a couple quick disconnects, the whole system can be completely modular for times when you need more space.


Harbor Freight Tools

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