OBA system

I didn't take any pictures of the bracket before putting it in place (got ahead of myself), so pictures of just the bracket don't exist. I did take a couple of the assembly in place. Control logic is dictated by soon to be service air horns (from a Peterbuilt), so there must be air pressure when the truck is running. The tank and compressor came with a pressure switch and I added a 50A waterproof circuit breaker, an 80A constant duty solenoid, a 'Sugar Cube' relay, and a Weatherpack inline fuse holder. A signal from an ignition only source will close the relay which will connect the pressure switch to the solenoid. The whole system is protected by the breaker and the controls circuit is protected by a 15A fuse in the holder. All but the breaker & the pressure switch are bolted to the compressor bracket.

The main part of the bracket has a pair of angle steel pieces that ride on the top-inner and top-outer corners of the frame rail, then there is the tensioner strap that catches the lip of the lower flange and is pulled tight by the pair of long bolts. Originally I was going to weld the strap to the threaded block, but I realized that bolting it would allow for mis-alignment and might make assembly easier.

I expect that the compressor's discharge temperature will be quite high at times, so the first 10 feet or so of plumbing is 3/8" copper tubing arranged as a condensor. I'm also using a coil of it as vibration relief to make the jump from the rubber isolated compressor to the frame.

Can see some of the tubing and electrical here, white wire is Ancor Duplex power and ground wires, the single weatherpack is for the IGN signal, and the double weatherpack connects to the pressure switch:


Better view of the condensor plumbing:


The vibration coil and the air inlet filter are visible here, the large white wire in the foreground is the camper's pair of 6ga. wires. I'll be tapping into those for power and ground for the OBA system. Just out of view is a double 3/8" isolated stud bolted to the frame for this purpose.

Got the tank in last night and pressurized the system for the first time. The compressor is surprisingly fast given the 2.5 gallon tank. I'll guess 3-4 minutes to pressurize the whole system.

The pressure switch was set really low at 80 psi. I had previously looked it up and knew that I could adjust it. Took a little bit of back and forth, but I now have it set at 145 psi. The switch appears to have a 20 psi hysteresis so that makes the system's low 125 psi. I'm thinking that I might back off the adjustment a little more, say somewhere around 130 psi for the high.

Once I have that set I'll adjust the over-pressure safety valve that I found in the "hardware store" to be slightly above the set pressure.

Had a leak that drained it overnight, but I want to change around some of the plumbing where the leak is anyway. It's a little too exposed.

Pretty nice,

I wanted to give you a heads up on the copper lines to monitor them. I once ran them for oil lines on a motorcycle and had constant leaks. An older mechanic told me to remove them and run plastic or steel because the vibration causes wear and stress cracks in the soft copper, particularly at joints.

120 to 130 psi is what truck air systems generally run FYI. I am curious what you guys with these setups run into with road and trail dirt, etc. on the compressors. Keep us posted! And thanks for sharing.

With that relay in there does it power up after the starter is done cranking?

Copper does work harden from vibration and then if allowed to continue it will crack. Neither steel nor plastic work as well for heat rejection, copper is one of the best for this use which is why I chose it. In my past experience the key to longevity seems to be for there to be enough length in the copper to allow the work hardening-inducing vibration to be spread out. Another crack promoter seems to be when the run is pulled tight like a guitar string. We'll see if the multiple bends etc. works here or not. On the trial run only the first couple of loops were warm, suggesting that it could be shorter from a purely heat rejection point. Occurs to me that annealing the flares might be a good idea.

The IGN source that energizes the relay is only live in run mode. It is dead in crank mode. Got lucky in finding it.

Got the plumbing changes done and have been working on the air horn system. I have the solenoid/manifold/mounting block built and have been working on its mounting bracket. Once that is in place I'll pressurize the system again and start a serious patrol for leaks. I'd like the system to hold pressure within the pressure switch's hysteresis over several days.

You must have found an accessory circut wire to tap into. I do not understand why you need the sugar cube relay. Can't you trigger the solenoid directly from the accessory circut?

CWD

I probably can, but since I don't know what all else is on that circuit I wanted to minimize my impact on it. Including the relay was the easier path.