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To start I am a senior in college studying mechanical engineering so electrical work can be terrifying sometimes :worried: I like the ease of a CO2 tank but I don't want to use CO2 in my wheels and tires because I don't fill them up very frequently and the idea that CO2 seeps out of tires over time shifted my focus to an air compressor and tank set up. On top of this the compressor and tank would provide air for tires as well as emergency use of an impact and air ratchet for short periods of time. I am planning a modified version of the Heavy duty OBA system by viair

The problem I ran into is wiring the pressure switch. The Viair pressure switch looks like it is supposed to be wired in series with the source to control power to the compressor and keep the pressure between 110PSI-145PSI. I want to put the tank in the back of the FJ trunk above the jack compartment. If I am running the pressure switch in series with the source then I would have to run wires to and from the pressure switch before connecting it to the compressor.

I have 2 wiring ideas attached. The first uses one relay with the pressure switch in series. The second one uses 2 relays and runs the pressure switch off of the fuse block. I had to delete multisim from my computer so I apologize for the visio drawings of the circuit. :lookaround: Can anybody with some electrical knowledge help me figure out the correct way to wire the pressure switch in? I always feel like I am going to catch my FJ on fire..
 

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Neither of your diagrams accurately represent a wiring setup that will work correctly.

As an alternative, here's an on-board air compressor setup that uses only aircraft or marine quality components and contains several levels of circuit protection redundancy.

https://www.fjcruiserforums.com/for...5-board-arb-air-power-distribution-panel.html

You don't want the pressure switch to directly control the compressor motor, the contacts are only rated for a few amps, not the 40+ amps peak DC current the compressor will draw. Switching DC is a much more severe application than switching AC because of the arcing that occurs at the relay contacts when switching off the compressor when it is drawing maximum current.

Use the Normally Closed contacts on the pressure switch to control an appropriately-rated normally-open relay (40-50A contact rating recommended). Place a marine or aircraft circuit breaker near the B+ supply source to protect the wiring and the compressor motor.

Required wire gage for the compressor motor circuit will depend on the maximum full-load current and the total length of wire required. Blue Sea makes a wide variety of high quality electrical system components for marine use that are well suited for an off-road vehicle. See their Wire Gage Selection Chart at:

https://www.bluesea.com/support/art...oosing_the_Correct_Wire_Size_for_a_DC_Circuit

There is a lot of technical info on the Blue Sea site that will help you understand 12V DC electrical systems, appropriate overcurrent protection, etc. Always include a readily-accessible master cutoff switch somewhere that can kill power to the circuit in case the relay contacts weld shut, the pressure switch fails, or some other circuit fault keeps the relay energized and the compressor running past the desired shutoff pressure. Obviously any air reservoir must also be protected with a pressure relief valve.
 

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