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on board air and dual batteries in a WJ

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finally finished my setup and wanted to put together a writeup over the next few posts...


ok so it's not dual batteries yet, but everything is ready for the second battery and dual controller, i just have to plunk down the cash for those items.


Here’s the compressors in the old battery location:




and here’s the battery and air tank:




the second battery will go in that empty rectangle, using the same hold down as the other one. the dual battery controller will go in the empty spot just to the right of the battery that's there now. that will leave me with 2 little triangles next to the second battery of empty space to store a few spare parts.

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With the 4.7L V8, space is extremely limited within the engine bay:




if I was just going for dual batteries, i might have considered a setup like this:




That’s a custom battery tray and hold-down in the stock battery location, with 2 Optimas. I think those are group 31 which are smaller physically, with less amp-hours and cranking-amps than the V8 Grand Cherokee’s factory group 65 battery, but since you have duals who cares! Note the picture above is from a right-hand-drive grand Cherokee, but the battery stuff is all still in the same place as ours here in the US.


Also if just wanting a backup battery, Odyssey makes a very small, low amp-hour, yet high cranking-amp battery called the PC925, and they have a trick bracket to go with it:




That little setup could probably be squeezed into quite a few little nooks that one could find in the WJ.


As far as actuall brand of battery, I used to be an Optima fan, but they have been getting a lot of bad press on the forums for the past couple years and it seems their quality control has gone out the window.


Odyssey was the other brand of sealed AGM battery that I had heard of several times before, with nothing but good reviews for them other than being a bit pricey. Then I heard that the Sears Platinum battery was a re-badged Odyssey for about 1/3 less money and with a 4 year warranty. I found a press release on the net stating that Enersys (Odyssey’s parent company) is indeed making the Sears Platinums, and then I even found a forum post on Expedition Exchange where someone emailed Enersys and they responded that yes it was a rebadged Odyssey… good enough for me.

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The whole idea for using the spare tire area for air tank came from someone on JeepForum. The spare tire well area is pretty useless as soon as you go to bigger tires, and just begs for some inventive purpose. Here was his setup:




My biggest concern about running like that would be that I think you would need to open the false floor whenever using the compressors so that they could get enough air to pump as well as to circulate around them for cooling. I could swear the guy told me he did in fact have problems with them overheating eventually, but I can’t find that post now, so perhaps I was dreaming.


So then the idea hit me, why not put the 2 batteries in the spare tire well, and put the compressors up under the hood. Sure it gets hot under the hood, but most everyone with TJ’s/JK’s mounts compressors there and they seem to work just fine. This would give me room for dual compressors and dual batteries and a small hot dog tank for air reserve… sweet!


So I did some measuring and it turned out that if I cut the removed the feet from a common air tank that is sold on ebay, I would actually be able to fit a full 5 gallon one in there and still have room for the batteries.




As far as compressors were concerned, I already had owned the common Masterflow MF-1050 / MV-50 that I got at Pepboys for $30 or $40 bucks, for like 7 years and it was still ticking. It had definitely slowed down a notch in the past couple years, but still that’s pretty good for a no-maintenance cheap piece of hardware. There’s a review out there somewhere that I can’t seem to find again that compared several of the common 12v compressors and the Masterflow was able to pump the same CFM as some of the much more expensive units. Then one day Costco started stocking them and selling them for $50, so I went ahead a grabbed 2 more thinking ahead to this project.




I briefly considered getting a really nice compressor, and when these die I may still. Some of the nicest that I am aware of are the ExtremeAire and ExtremeAire Magnum, but they are $400+ and $500+ respectively.


Then of course there’s engine-powered air. It’s the ultimate, but there are 2 huge reason I didn’t go this route. 1 – I wasn’t about to give up my A/C to convert it to air. 2 – I don’t have the necessary fab skills (nor do I know if it’s even feasible) to redo all the accessory mounts on the engine so that a second A/C (converted to air) could be mounted.

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Some sort of frame was going to need to be created to mount the batteries and air tank in the spare tire well. Tire well has the plastic factory gas tank wedged in right below it, so that meant no easy screwing or welding to the floor of the well…


So I had some basic ideas of what I wanted, and went over to see George and he really made it happen for me. We even went ahead and made an access door for the gas tank pump/sending unit so that it can be easily accessed without dropping the tank.


Here is the full thread on how he created and attached the frame: http://www.offroadpassport.com/forum/showthread.php?t=321


And here are just a couple quick pics of it:






the battery is attached using a hold-down that consists of a couple j-hook rods and rubber strap that is available at any autoparts store or Sears:




the tank attaches with bungee cords. this way it can be easily removed to access the gas tank pump trap door or to take the tank out and drain water occasionally:




then i had to notch out just a little bit of the false floor door for that final 1/4 inch of clearance so that it would close properly:



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Mounting the compressors was pretty easy. The factory battery tray needed to be Dremeled out in a few places to make just enough width for the compressors to sit off-set side by side. The underside of the tray needed to have some if it’s ribs removed so that screws holding the compressors could sit flat.




Other than that I just ended up putting a flat thin piece of steel in the bottom of the tray so that the compressors could sit level. The factory tray has a bunch of little channels in it and no matter what I did, at least one mounting area would end up in a channel or hole.


As far as the compressors themselves, I removed the rubber feet and replaced them with rubber grommets. I made sure to use plenty of LockTite on the mounting bolts since there will be constant vibration wanting to loosen everything.





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I believe the consensus is that the compressors use 1/8 BSPT fittings, but that you can just use the common 1/8 NPT fittings with plenty of Teflon tape. Now before I knew this, I had decided to just drill out and tap the compressors for the really common 1/4 NPT fittings… oh well, a little time wasted I guess.


Here’s the compressors as it comes:




And here’s me modding it:






And here’s 2 finished compressors with 1/4 press-fit plastic air line fittings for their outputs where they used to have gauges, and the other output plugged:




Several people on the net have figured out you can get a much cheaper solenoid for your ARB locker than the ARB branded one. More info here http://www.stu-offroad.com/axle/mac/mac-1.htm


The other special item I used was the Viair 4 way multi-port. It has a 1/4 Male, then (2) 1/4 female and (1) 1/8 female. I plugged all but 2 of the 1/4 NPT holes on the air tank and then 2 of these little multi-ports worked perfect for all my needs.




The bottom of both of those screw into the air tank.


The multi-port on the left in the pic – has a barbed 1/4 hose fitting for my main output which goes eventually to a quick connect, then on top there is a plug (which I ended up replacing with a gauge just to make sure the pressure switch and blow-off were working correctly), and then the arb solenoid uses the 1/8 port on the right.


The multi-port on the right in the pic – has a 1/4 press tube fitting for the air coming from the compressors, that goes into a 1-way check valve to keep air from bleeding back out, then a 125 PSI blow-off safety valve on top, and finally the 1/8 port on the right is connected to a Viair pressure switch that cuts on at 85 PSI and off at 105 PSI (the working range for the ARB locker).


Here you can see how those work with the tank and all the incoming/outgoing lines:




and here is the quick connect fitting to connect to for filling up tires and running air tools. i couldn't find a better place for it than this, but if i ever get a custom rear bumper, i'll make a recess for it and move it there:




I got all the Viair stuff from http://www.suspensionconnection.com


I got the quick-connects and coiled hose from http://www.expeditionexchange.com/cart/home.php?cat=280


I got nearly all of the other fittings and hose from http://www.grainger.com

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For consistency, I used all Stinger brand wire, connectors, terminals, etc., and I got everything from http://www.hifisoundconnection.com


First step was removing the old battery terminals, and connecting the large 1/0 gauge wire that would be run to the back of the vehicle in place of them. For this I used a (1) 1/0 GA to (2) 4 GA distribution terminal stripped of all it’s plastic trim.








Here’s both the positive and negative done up, and then everything covered nicely in split loom:






I chose to run everything over the engine then down to the driver side frame rail and follow the existing fuel and evap system lines to the back. You can’t run down the passenger side because the interior of the pseudo-frame rail runs within an inch of the cat and muffler which could surely melt wire insulation.


More split-loom and zip-ties (yes I’m a fan of both)!




I used the 1” hole Stinger Pro Grommets wherever going into the cab area. They are adjustable and will seal even slightly irregular shaped cables from about 1/2" to 3/4" in diameter. Smaller sizes are available as well.




I used more Stinger stuff for a fuse mounted near the battery in case of any shorts, and for the battery terminals which connect to the cable via large ring-terminal.






When I get the dual battery controller and second battery, I’ll move those single ring position terminals to the second battery and put dual ring terminal ones on the main battery in order to get 2 feeds to tie everything together.




One thing I chose to do which some people might consider a waste was to run a full ground wire all the way to the back instead of grounding the front former battery wires to the body and then grounding the new battery in the back to the body as well. I just feel better not having to worry about 2 ground connections that could corrode or come loose that the entire system depends on. Some might feel exactly the same about a single wire… to each his own.


Within the cabin, I already had one auxiliary switch, and plans for some rock lights soon and other items that need switches, and of course now I had to also put in switches for the air compressor and the front locker.


Here’s what I came up with. I of course had to go to 3 different stores to find enough switches with the amber indicator to match the factory switches which all have amber indicators!


First bent and drilled some sheet aluminum:




Then wired up the switches to a 12 position disconnect from Radioshack:




All mounted just a bit recessed in a factory cubby hole that I never found much use for:






And here’s the final product with a couple switches on:




There’s still room for an entire row of 4 more switches below that set as my accessory list grows.



EDIT ----


one thing if forgot to mention is that those little compressors actually have relays built into the butt end of them - i'm not sure why they used that instead of just using an appropriately rated switch... unless perhaps they are more than a relay and have a thermal shutdown built into them or something... anyway, just take apart the 4 screws holding the end-cap on and you can splice into that relay to turn on the compressors with your interior switch, there's no use adding even more external relays, just more cost and more complexity.

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it hasn't been on a trip yet and hasn't even been assembled for many days so let's just hope nothing overheats, explodes, melts or shorts out!


i jacked up one side of the front to spin the wheel, then hit the locker switch and tried to spin it again to verify locker operation, but have yet to test it on the trail.


- so far the only problem is that the system will leak down from 105 PSI to about 75 PSI in 10 hours, then it will hold there for days. on my final air output to my quick disconnect, i used regular air hose on barbed fittings with hose clamps. i think this is the weak link in the system and probably where the leak is because all the other fittings were done nice and tight and with plenty of Teflon thread compound. i will replace that hose/fittings with the same 1/4 plastic line and compression fittings perhaps, but for now that slow of a leak is a total can-live-with.


- also i used the 5 mm or 5.5 mm or whatever it is blue air hose that come with the ARB for it. i want to swap this over to standard 1/4" plastic tube like i have coming from the compressors. that way the entire system is the same and i only need to carry one piece of spare tube and splice connectors.


stay tuned for long term testing!

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i have a nice quality PowerTank SuperFlex Braided High Pressure Coiled Hose for airing up the tires and running small air tools and now i just want to get the PowerTank bad-ass High-Flow HD Inflator with bleed button and liquid-filled-gauge! yes i like quality toys ;)





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costco compressors 2 @ $50 = $100

ebay air tank = $90

sears platinum battery = $180

1/0 gauge stinger battery wire = $110

misc wire, split loom, connectors, terminals, zip ties, grommets, switches, etc. ~ $125

misc hose, tubing, air fittings, solenoid, etc. ~ $100

misc steel, aluminum, screws, paint, grinder discs, drill bits, etc. ~ $50


i'm estimating on some of that, so the total is around $755 to $800 and a lot of personal time.


sounds like a lot, but all the little stuff adds up quick, and good wire and a good battery isn't cheap either. If you use cheaper low strand count battery wire, and in general just don't go for the best of everything you could do it a lot cheaper. also, i've been slowly sourcing all of this stuff for the past 6 months, so it wasn't one big bill.


if i get the nicest dual battery controller and another of the same batteries, that will be $375 + $180 more, so then there will be over $1,300 invested... wow. then of course i need to still get a fridge and a winch one day to justify all that reserve battery power! ;)

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