Rednroll

I've been working on an onboard air project build and am getting close to wrapping up. Thought I would share.

Target Goals of this system.
1. Inexpensive (<$200)
2. Does not take up interior cabin space
3. Ready-to-use with minimal fuss (ie no unpacking/repacking hoses, wires, crawling under vehicle, opening hood, etc.)
4. Exterior hidden mounting location
5. Able to fill (4) 35in tires from 15psi back to 35psi with no wait down-times (due to air compressor overheat)
6. Target tire fill-up time (4 tires) <20min
7. Water/Environment resistant
8. Simple removal/access for any maintenance
9. Backup reliability system
10. No C02 system inconveniences (tank storage/mounting, run out of CO2, need to refill tanks).
11. No more searching for a fill up station with an air compressor if my tires are low.


Parts List/Price
Harbor Freight
(2) 12Volt 150 PSI High Volume Air Compressor (25% OFF coupon) $49x2= $98
200 Piece Self-Drill Screw Assortment (20% OFF)=$7.20
100 Pack 11in Black Cable Ties=$2
9PC Heat Shrink Tubing Assortment=$1.29
1/4"x14' Protective Wire Wrap $3.49x2=$7
Threadlocker Locktite Red&Blue= $4.50
Home Depot
5/16" x 48" Steel Rod=$5
1 1/2" Metal Ring (2PK)=$2
9/16" Rope Loop $1.55x2=$3.10
Walmart
3M 28PK Assorted Electrical Connectors=$4
Permatex Clear RTV Silicone Adhesive Sealant=$4
Ebay
10 Gauge RED Flexible Wire 100Ft=$17
5 Pack 12" 10 Gauge 2 Pin Quick Disconnect Harness=$13

Total Cost: $168.09

Overview:

A key element to this setup is that I'm using (2) separate High Volume air Compressors. Most that I have spoken with, said they were able to fill up (3) 35's, using a single HF compressor until the compressor reached a point of getting hot and needing cool down time. My overall take away after reading other's comments on these compressors was that it either shut down during the fill up of the 3rd tire, or the beginning of filling up the 4th. This seems to be the case with a Viair 400P as well which is a similar size name brand compressor.

To avoid the potential shut-down wait cool down period, I have decided to purchase 2 of them and mount one on each side of the vehicle. Therefore, each compressor will only be filling (2) 35in tires.

My thoughts on using 2 compressors instead of 1 would give me the following benefits.
1. If cool down was needed, I could continue filling with the other while the heated one was cooling down. Thus, no down time.
2. Since it seems to be common that each compressor is able to fill up to (3) 35in tires before needing cool down, and limiting each compressor to filling up 2 tires, I may be able to avoid any cool down wait period and additionally be able to fill up (2) tires simultaneously thus decreasing overall fill up time.
3. If one air compressor fails for whatever reason, I still have a functional back-up. I may even purchase a 3rd one and keep it inside since I made this setup so it is pretty much easy swap, plug and play.
4. Since (1) compressor will be mounted on each side of the vehicle, I won't have to drag any hoses under my vehicle. Driver side compressor, fills up 2 driver side tires, passenger side compressor fills 2 passenger side tires.
5. Even if I add a back-up which would make (3) compressors @$50/ea, I'm still below the cost of a single Viair 400P.

Rednroll

Tools used in-case you would like to do a similar build

Tools
Philips Head screwdriver
Wrenches 8mm, 10mm
1/4in Ratchet
Sockets 8mm, 1/4"
Wire Cutters
Pliers
Angle Grinder
Bench Grinder
Soldering Iron
Flux Welder (90A)
Bench Vise
Heat Gun
Drill/Multiple bits
3/8 in. 90° Angle Drill Attachment
Jig Saw/metal cutting blade
Measuring Square
Hammer
Wire Brush

Misc Supplies
Black Truck Bed Coating rattle can
White Self-etching primer rattle can
14in wire tires
Silicone sealer
Soldier
Shrink Tubing
Black Plasti-dip
Electrical tape
Red & Blue Thread Locker/Loc-tite

Rednroll

The 1st things I had to do was make some minor Mods/enhancements to the air compressors(X2) to meet these goal criteria 7,8, & 9.

7. Water/Environment resistant
8. Simple removal/access for any maintenance
9. Backup reliability system


I already know I'm not using a top branded air compressor. However, when selecting my install locations I didn't want to risk damaging or theft of a more expensive name brand unit such as a Viair. So a $50 compressor made sense for my application, where others have reported the HF compressor have worked well for them, as long as you do some minor occasional maintenance before use. One of those items for a longer life of the HF compressor is that although it is a maintenance free compressor, a shot of lubricant in the air intake end such as WD40 or Lithium based liquid wrench every now and then and before use will keep it running cooler and lasting longer.


To make it water resistant I decided to take it apart and silicone seal the electronics side. Additionally, I replaced the main power wires with a 2 pin quick disconnect shorter wire harness.

Compressor Disassembly




What's inside?


There's not much inside of these in regards to electronics. It's basically a DC motor with an on/off power switch, a fuse, and a thermal cut-off switch. The thermal switches function is that it is a switch that is normally on/closed. When it heats up to a certain temperature, this switch turns off/open thus, cutting power to the DC motor. A thing of interest if you've had a similar air compressor fail on you where it will no longer turn on and you've already checked the fuse. The weakest link after the fuse, is the thermal cut-off switch where they often fail to stop working and fail in the Off/open state. To fix this problem you could replace the thermal switch or just connect the black and blue wires together, thus bypassing the switch. However, when you bypass the thermal switch, the coils in the DC motor now become the weakest link for potential failure. The coil windings in the motor heat up, get too hot and then the insulation melts and the motor fails. However, better than not working in the event the thermal switch failed previously.

Power Wires/Silicone sealant mods

I purchased 2 Pin quick disconnect harnesses to replace the existing power wires. I de-soldered the existing black power wires and soldered the 2 Pin quick disconnect in its place. You just need to make sure the RED wire goes to the "POS(+) PWR Wire Connection" location and the Black to the "NEG(-) PWR Wire Connection" location.

Take note of which end of the 2 pin connector connects to the compressor to avoid potential electrical short conditions if the compressor's power lines are disconnected while using the 2 pin quick disconnect.

After that I silicone sealed all the openings (fuse holder, power wire, switch) in the plastic end cap and put a generous amount of silicone around the edges of the end cap to form a gasket.


Then just re-assemble the 4 screws/nuts of the end cap. An important note before assembly of the end cap. You can rotate the orientation of the end cap. I am mounting these compressors under my vehicle mounted sideways. I rotated the end cap so the switch would be the furthest point facing down towards the ground, so the switch was easier to reach when reaching under the vehicle to turn the compressors on/off for use. This also puts the power wires closest to the vehicle, thus reducing the chances of them hanging down and getting snagged on something.


Bottom Base Plate Mod (JK Mounting prep)

With the bottom plate previously removed, remove the rubber surround and 4 rubber feet from the plate.

I used (6) #10 3/4" self tapping sheet metal screws to mount the compressors to the vehicle. I modded the compressors bottom base plate, to be used as the vehicle mount attachment.


*Note: Don't reassemble the plate to the compressor at this point, the plate will need to be used as a template to mark the screw locations on the vehicle for mounting.

Rednroll

As the title of the thread says, "ready-to-use". Which means as well as having the compressors mounted outside of the vehicle, with electrical connections, I also wanted the air hose attached to the compressor with the goal for the hose to be able to reach all 4 tires if necessary but mainly to reach the front and rear tire on the side each compressor was mounted on.

The intent here is if I need to fill a tire, I can just turn on the power switch of the air compressor and pull out the hose to the tire with minimal fuss.

Here's the HF air hose attachment, I'm trying to hang.


I shopped around for something that would work as a hose hanger but didn't find anything. Therefore, I decided to just make something that I was looking for instead.

Air Hose Hanger fab

I went to Home Depot and purchased a 5/16" x 48in steel rod which ended up being the perfect length to make both hose hangers.


Next I had to do some measurements of the hose, and the available clearance between the frame rails and pinch seem where I was mounting the compressor.

- Start by cutting the rod in half.
- I used a bench vise and a hammer to bend the steel rod into 90 deg bends and checked them with a square. Nothing sophisticated.


Here are the dimension lengths of the bend points. The Steel rod in an "S" shape. The order I made the bends is shown (B1, B2, & B3).


The yellow mark needs to be bent directly upwards. This is what will be used to prevent the hose from sliding off the rod.

When bending is complete, I have (2) rods that look like this. Top= Passenger side, Bottom= Driver side.


These rods will mount to the outer frame rail in front of the air compressor's mounting location. So time to make a mount for the rods. I needed a piece of metal that was about a 1/4in thick, and 4-5in in length to weld onto the rods. I looked around and found some extra TF brackets from my tire carrier that I wasn't using. These will work just fine.


Use Flux welder to weld the TF brackets onto the steel rods. Note....I suck at welding, but as long as they stick together I'm happy. They are meant to be hidden.




All welded and bent into shape, time for some mounting holes. Then put it on the bench grinder to smooth down the sharp edges and grind down my weld dots.
Top= Driver side, Bottom=Passenger side.


Rattle can Primed


Poor man's powder coat (few coats of Rattle can black Truck bed Liner)


The hose hanger held up the yellow portion of the air hose, but I still needed something to keep the black rubber portion from hanging down. I made a loop hook.

Hose Hanger Loops

Items used from home depot: I will mount and hang the ring from the rope loop and then put the rubber hose end through the ring to hang the hose end.


I didn't want them jingle like Santa Clauses sleigh, so I Plasti Dipped the rings.

Plasti Dip Ring

Rednroll

Air Compressor Mounting

The location I found to work best for me, was mounting the air compressor onto the outside of the frame rails, between the frame rail and the pinch seam. The locations I used were between the rear body mount (infront of the rear tire) and the Mid body mount. In both directions, it ended up being the perfect amount of space available to be able to fit the HF compressor, as well gave me a sturdy and secure mounting point using the sides of the frame rail.

This required some drilling into the frame rail for the mounting screws. I found this 90 Deg drill attachment to be very useful to be able to drill holes in this space between the frame rail and the pinch seam. Going straight at it with a drill would be difficult unless you have a small high speed drill.



Using the compressor base plate as a template, drill (6) mounting holes into the frame rail as shown. The compressor needs to be mounted so the air hose is facing towards the front of the vehicle. Since I am mounting (2) compressors, this procedure needs to be mirrored on the driver's side. Be sure the base plate is facing the correct direction before drilling. I used (6) #10 3/4in self threading sheet metal screws for mounting the air compressor. Thread the screws in about a 1/4". SEE POST #18 FOR UPDATED MOUNTING LOCATION IMPROVEMENT AND ADDITIONAL DETAILS.



Now re-assemble the base plate back onto the air compressor with the (4) screws, nuts, and rubber grommets that came on the compressor. Use some RED loc-tite, so these screws don't loosen up over time. Put the rubber edge protector back on the base plate. Discard the original rubber feet, they can't be used for this mount. Slide the compressor over the mounting screws in the frame rails, then slide forward to lock into place. Tighten (6) #10 3/4in screws. The rubber edge protector works great as an anti-rattle seal to keep the compressor base plate firm and from rattling against the frame rail while driving.

Compressor Mounted (Passenger side)


Compressor Mounted (Driver side)

* Did I mention the rebranding mod I did to the compressor as well? I just finished doing a TF rear tire carrier install and this seemed like a perfect fit for their provided stickers.

Hose Hanger Install
I used (3) #10 1/2" self taping sheet metal screws and put some Blue Loc-tite on the threads. The hangers are mounted about 4-5in in front of the MID body mount.

Passenger Side Hose Hanger


Driver Side Hose Hanger


Hose Hanger with Air Hose hung


So as you can see from above photo, the air hose is hung but the rubber attachment end is still hanging down.

Hose Hanger Loop install

I drilled (2) holes and used (2) #8 5/8" sheet metal screws with blue loc-tite to mount.


Problem solved, air hose is now fully hung.





So how's it look from the outside?

View from outside

Nothing hanging down


Getting up close you can see a little bit of the compressor sticking out between the crack of the side step


And the yellow hose can be seen between the crack of the side step

Rednroll

I soldered on the mating side of the 2 pin connector to about 20ft (driver side) and 15ft (passenger side) of 10 AWG red wire and then wrapped the wire in plastic wire loom for added protection and safety. The black wire of the 2 pin mating connector was connected directly the chassis as shown. The connector for Ground was soldered on to the black wire.


Connect 2 pin connectors together and tuck up above the body mount, so they aren't hanging down.


Run the Positive wire up into the side rails, and then through the frame rails and up into the engine bay.


Zip tie pos wire to existing wire harness loom.


Connect both compressors to fuse connection of Positive battery post. I connected and shared my already existing winch fuse to keep things simple and tidy, since I won't ever be using my winch and air compressors simultaneously.

Rednroll

Test 1: Individual Tire Fill-up Time Test

Tire= BFG TA KO2 315/70/R17 (35in) mounted on 17x9 Wheel
Outside Temperature= 53Deg F
Start Pressure= 15psi
End Pressure= 35psi
Average Fill Time= 3:10

I ran the above test 5 separate times to get to the AVG time. The 1st test I did, I let the tire fill for 4:00 and was shocked when I took the pressure reading that it was sitting at 42psi. I wasn't expecting it to be able to fill the tire that fast. I then ran it with a 3min fill up time and I was at 33.5psi. Test at 3:20 fill time gave me 37psi. I eventually zeroed in on the average time where it seems to take just over 3min to fill a single tire from 15 to 35psi.

Next I'm going to run a speed test and see how fast I can fill up all 4 tires from 15-35psi. Based on the individual tire test, I see no problems being able to hit my <20min original target. I see no reason I shouldn't be able to fill all 4 tires up within 15 minutes, including the time to walk around the Jeep, disconnecting and reconnecting the compressors from each tire.

So far the HF compressors are exceeding my expectation in regards to their fill up time.

Test 2: Simultaneous Tire Fill-up Time Test. Fill 4 tires from 15psi to 35psi, using both compressors running simultaneously.

Tires= (4) BFG TA KO2 315/70/R17 (35in) mounted on 17x9 Wheel
Outside Temperature= 80Deg F
Start Pressure= 15psi
End Pressure= 35psi
Total Fill Time= 9:05

From the Google Playstore, I installed the app "Multi Timer" on my phone and set it up as such.
(4) Countdown Timers set at 3min each, 1 Timer for each tire.


It also has a separate screen for a Stopwatch.


Fill up steps and timing procedure.
1. Turn on Compressor 1 (Driver side compressor)

2. Start Filling L/F Tire with Compressor 1, START Stop Watch, Start L/F Timer.
3. Walk to passenger side, turn on Compressor 2(Passenger side Compressor)
4. Wait for L/F Timer to reach 2min in countdown.

5. Start Filling R/F Tire, Start R/F Timer.
6. Wait for L/F Timer to expire, disconnect Compressor 1

7. Start Filling L/R Tire with Compressor 1, Start L/R Timer.
8. Check L/F Tire Pressure= 36.5psi
9. Deflate excess air from L/F Tire to 35psi
10. Wait for R/F Timer to expire, disconnect Compressor 2

11. Start Filling R/R Tire with Compressor 2, Start R/R Timer.
12. Check R/F Tire pressure= 32.5psi
13. Wait for L/R Timer to expire, disconnect Compressor 1
14. Check L/R Tire pressure= 36.5psi
15. Deflate excess air from L/R Tire to 35psi
16. Wait for R/R Timer to expire, disconnect Compressor 2
17. Check R/R Tire pressure= 33.5psi
18. Reconnect Compressor 2, to R/R tire and finish inflating to 35psi
19. Reconnect Compressor 2, to R/F tire and finish inflating to 35psi
20. STOP Stop Watch= 9:05



I'm impressed. My target time was less than 20min.....I was able to fill all 4 tires in half that time.

Rednroll

Backup to the Backup.

With the Compressors and hoses being mounted underneath the vehicle, I just wasn't sure what problems I might run into if I happen to venture through some water crossing, or what would happen after spending a day in the sand dunes. I figured it's better to be safe than sorry.

This past 4th of July I received another one of Harbor Freight's 25% off coupons and coincidentally the original price was also lower. That put the price of the compressor at $45!!! At that price, I decided to purchase a 3rd compressor to stick in a bag and store on the inside, under my back seat for those "just in case" purposes.

However, I wanted to make the back up convenient to be able to meet multiple use cases such as.....
1. I could easily connect it into my existing onboard air setup to use as a backup replacement.
2. I could connect it directly to my battery to assist a fellow offroader if needed.
3. I could hand it to a friend to borrow if he needed to use it to air up his rig.

To do this, I modded the power wires, so that they had the same 2 pin quick disconnect connectors and could be directly plugged into the power wires that I ran to the chassis mounted compressors.

The HF compressors come with 11ft of power wire with battery connector clamps on them. I decided 11ft might not be quite long enough to be able to connect to my battery and reach over to a fellow foes vehicle. Well, fortunately, I had 2 other 11ft runs of power wires that I cut off from the 2 other compressors that I mounted.

What I ended up doing was that I cut the battery clamps off of this backup compressor, leaving about 9 feet of existing power wire, then soldered on a 2 pin quick connect. With one of the 11ft set of power wires from the original compressors, I soldered on the mating side 2 pin quick connect. By joining these 2 wire runs together with the quick connects, I now have a 20ft length of wire on the back up compressor that can be directly connected to my battery terminals. If I disconnect the 2 pin connectors, I have 9ft of wire to set the compressor on the ground and directly plug it into the power wires on either side where the other compressors connect for power.

The HF compressor out of the bag.


Cut off battery clamps, and replace with 2 pin quick connector, soldering the wires together. Make sure your battery polarity remains intact (ie Positive wire to Positive wire, and Negative wire to Negative wire).



Put shrink tube around the individual POS and NEG wires, and then shrink tube them together for added protection. Compressor side connector shown (make note that POS pin wire is exposed, same as mounted compressors). Do the same soldering/shrink wrapping for the wire with the battery clamp connectors, using the mating 2 pin connector.


Connect to onboard air install wiring connection option. (9ft of power wire with 2 pin quick connect)


Connect to battery terminals or let someone borrow option. (20ft of power wire with battery post clamps)


Put the backup compressor in the bag it came in and throw it under the back seat. $45 of additional piece of mind, and added convenience.

dahreno

The very first thing on your parts list will probably make you fail your mission. I've had two of the same compressors and it not only will fail to fill your tires up that fast but will also crap out when it get hot, making you wait for cool off. Sorry !

Rednroll

There's a reason, there are 2 of them. I planned ahead for that. Further details coming.