OBA -> On Board Air Mega Thread & BS

I just installed the viair 400p automatic with the expedition essentials bedside mount and I love it

 

Hi there, are there any engine bay mounts specifically for the ARB single? Seems like the Slee and Rago mounts are quite a bit bigger than necessary, yeah? Thanks!

 

I think cbi makes one

 

They do, but it doesn't work for 20/21. Thanks!

 

Quick question about wiring and ampacity - I have #4 welding wire going from my battery (+ and -) to my bedside compartment (Doublecab Shortbed). From there I have a busbar that the ARB twin and a separate fuse panel go to. On that fuse panel I will have my fridge, bed lights and possible some led strip lighting for camping setup. When I turn the compressor on the bed lights dim, I haven't tried with the fridge yet. Does this mean I'm drawing too much and the #4 wire isn't enough?

Thank you all for any help - as a mechanical engineer this electrical wizardy is news to me. The #4 welding wire was run previously to installing the bedside compressor.


Setup:
15ish feet of #4 Gauge (power and ground) going from the battery back to the bedside
80A Breaker off the battery (should I step this up as well?)
Battery is XS Power Group 31 (But I only run the compressor with the truck on)

Accessories:
ARB Twin Compressor (two 40A inline fuses) 50A draw underload and 28A with no load
BlueSea Fuse Panel

Fuse panel has the following hooked up to it:
Snowmaster 42L Max 5.5A draw
Bed Lights are 2x Ebay 6 inch strip lights (honestly not sure how much these draw)

 

Wire sizing depends on both amp draw and length of run. But if the engine isn’t running when the compressor is on it’s not surprising the lights would dim. If it dims with the engine running as well then awg 2 or 0 might be in order. Also consider moving the compressor closer to the battery.

 

I'm curious if anyone has installed pressure gauges in the cab to monitor pressure in the locker. I'm starting to collect parts for the install and considering placement of the gauges. I plan to run mechanical gauges, one for each locker tied in at the solenoid. That way there is some positive feedback in the cab they are actually locked and holding pressure. It would also reflect any leaks on the locker side. It would be another pain in the ass install for the channel so I'm happy with that.

 

I bought some 1” gauges and use them to monitor tank and air bag pressure from a panel in the center cubby. The panel also has switches controlling solenoids to each use plus the compressor and a pressure regulator for control. I got the idea from Iggy’s panels but made it from ABS.

 

Took some inspiration from TW for my OBA setup. Installed an ARB twin last week near the windshield washer fluid reservoir.



It's a tight fit but with a 2nd gen slee mount bracket and a custom bracket I picked up on TW it fits nice. If I ever have to remove it I will probably have to remove the grill and headlight. I managed to install without removing either.



Wired up a custom switch harness to have the switch nearby. Re-pinned the ARB switch harness and added and inline fuse to a on/off waterproof switch.



Used ARB air fittings and air hose ran to a quick detach from wit's end mounted on an angle bracket I found online and spray painted. Used and existing threaded hole behind the grill to secure the bracket.



Just ordered an ARB hose and tire inflator to round out the setup.

 

@shiftd - FYI I went through about 5 of those rubber "waterproof" switches over the last 3 years. I opted against buying more because when they fail sometimes they switch on. Just be wary...

 

Thanks for the heads up. I'll keep an eye on it and consider swapping it out if I can find something better. For now the hose quick disconnect has a plug so the compressor shouldn't continue to run if it switches on but it's something to consider.

 

Test fitting for the right placement. I would have loved to retrofit an FJ Cruiser gauge set up but they are too large and super pricey.

 

Do you have any pics of that setup? I just recently found out that the expedition essentials mount will work with smittybilt/viair compressors, but I've only ever seen them with ARBs mounted. Also, how did you go about changing the wiring? If the viair is anything like the smittybilt, the wires are far too small for bed mounting. My concern is going from 4 gauge wire to the 10ish gauge wire inside the end cap. I don't want the remaining original wiring inside the cap to end up acting like a fuse and burning up.
Also, would anyone happen to have the measurements for the inside of the expedition essentials bedside mount? Never seen a smittybilt in one before, but I'd like to know if it would fit.

 

Larger gauge wire is required because of the voltage drop on the longer cable run. Smaller gauge is fine for shorter runs (like inside the compressor).

It should be fine running the larger gauge to the compressor and tying into the stock wiring on the compressor because internally it is for very short runs. This is very common. I have a power panel in my bed run off 2 10ga wires from my fuse box under the hood but then the wiring within the panel is all 14ga but that's all for 2 inch runs of wire.

It's not like higher end compressors are wired with welding cable internally. You'll be fine.

 

I can snap a picture tomorrow but despite the consensus of using thicker gauge wire I only had 8 gauge wire and ran it from the batter with a 40A breaker. I snipped the battery clamps that came attached to the compressor off and connected it to the 8awg wire with an Anderson disconnect plug. I’ve used it to air up multiple times and felt the wire to make sure it wasn’t heating up and I haven’t had any issues thus far. I live in AZ so if excess heat were a problem that hasn't done anything yet either. I’ve been super happy with the Viair 400p automatic and I think it’s a good bang for buck. If you’re doing the bedside install the Expedition Essential bedside box made it super easy. I can try to grab some basic measurements with the picture

 

Thanks, I'd really appreciate it. Also makes me feel better about the wiring situation. I wonder if it only pulls 45 amps when starting up and a lesser amount once it gets going? Either way I think I'll stick to 4 Gauge, but I think I might do a connector as you mentioned. I was just planning on a splice, but I think a plug would be way more convinient.

 

Make sure the connector terminals are rated for the current, it’s the most common failure point.

 

The manufacturer states the the Viair only draws 30A during operation so the startup is probably somewhere around 40A. I would hope my breaker would pop if it was higher than 40A and the Viair has a 40A in-line fuse that I decided to keep. The Anderson connector I used was rated for 50A

 

Here’s what it looks like. The dimensions of the box are loosely 6in deep, 17in wide, 8in tall give or take some. I was rushing to work this morning.
Here’s what the Anderson plug looks like. The real test will come when I air up both my tires and a buddy’s tires. If it passes that then I’ll be more then satisfied.

 

Good.
Amp draw<fuse or breaker<wire & connector capacity. There are other tables that make recommendations but I use the one at Powerstream because it lists the ohms per unit length for each wire gauge so I can determine the voltage drop for any given wire size/length and choose accordingly.
https://www.powerstream.com/Wire_Size.htm
Listed as ohms per 1000 ft and maximum chassis wiring current(conservative “rule of thumb values”). A few examples are:
Awg 6 - .3951 ohms, 101A
Awg 8 - .6282 ohms, 73A
Awg 10 - .9989 ohms, 55A
Awg 12 - 1.588 ohms, 41A
For a compressor in the passenger side rear cubby the wire length from the battery is going to be ~20’ more or less but for a complete circuit this gets doubled so 40’(40/1000=.040) The voltage drop @ 40A for:
#6 - .040 x .3951 x 40A = .632V
#8 - .040 x .6282 x 40A = 1.005V
#10 - .040 x .9989 x 40A = 1.598V
#12 - .040 x 1.588 x 40A = 2.54V
40A is within the “rule of thumb” guidelines for all of these wire sizes but which size you choose will affect performance. Shortening the wire run by choosing a mount location closer to the battery can alter which wire you choose. An engine bay location could allow #10 wire to outperform #6 wire to the cubby saving $ and weight.
This was just an example since there are other factors that go into where you decide to install an accessory. It just shows that wire length is just as significant as wire gauge on installations.