onboard compressor. quick question

I've got a compressor that I'm mounting in the cargo area of my xj. I understand this compressor can draw up to/around 30 amps.

I'm going to be hardwiring it with a auto type 30a blade fuse inline on the powerside, and will probably just run it up to the battery as there is an on/off switch on the compressor itself.

The PO of our house is a good friend and left some electrical supplies, which include several 6-10ft lengths of power cord (some with plugs, some without, that were leftovers from repairing various power tools/appliances, etc.).

These look to be about 12guage with three wires(I'd only use two). They're still wrapped in their protective sheath and are in really good shape.

anyone see any issue with me running this type of wire/bundle from the compressor up to the engine compartment (probably just to the battery itself) for my power supply? I'm going to run it as cleanly as possible, either along the door sills or along the headliner.

Thanks in advance for the feedback.

-Brian

I would strongly suggest using all 3 conductors of that cable in parallel as your positive, and grounding the compressor to the unibody - 12 gauge is only going to handle up to about 20 amps, with the motor drawing 30 it is going to warm up significantly. With all 3 in parallel you have a maximum load of around 60 amps, which leaves plenty of headroom.

Make sure you put the fuse as close as you can to the battery, that way more of the cabling is protected by it - anything between the fuse and the battery can cause an electrical fire if it shorts out against the frame (say a sharp metal edge wears through the insulation.)

Will the compressor automatically shut itself off at the max pressure? If it doesn't have a built in pressure limit switch you will want to install one to avoid damaging the compressor or even worse, exploding one of your lines or the tank itself.

It is advisable to run it through a relay and not put all the load on that switch. Also, make sure the compressor has a pressure switch. If it is an all inclusive unit with a tank, it probably has one already, but if you are adding your own tank, make sure it won't blow it up :wierd:

Floydargue said:

It is advisable to run it through a relay and not put all the load on that switch. Also, make sure the compressor has a pressure switch. If it is an all inclusive unit with a tank, it probably has one already, but if you are adding your own tank, make sure it won't blow it up :wierd:

Click to expand...

I'm not planning on running a tank at this time, and was thinking of putting a pressure switch in-line between the compressor and the hose quck-disconnect fitting.

Will that be sufficient for now?

You guys bring up some good points, I think I'll research some of the installs on the board a bit more and probably come back with some more questions...

kastein said:

I would strongly suggest using all 3 conductors of that cable in parallel as your positive, and grounding the compressor to the unibody - 12 gauge is only going to handle up to about 20 amps, with the motor drawing 30 it is going to warm up significantly. With all 3 in parallel you have a maximum load of around 60 amps, which leaves plenty of headroom.

Make sure you put the fuse as close as you can to the battery, that way more of the cabling is protected by it - anything between the fuse and the battery can cause an electrical fire if it shorts out against the frame (say a sharp metal edge wears through the insulation.)

Will the compressor automatically shut itself off at the max pressure? If it doesn't have a built in pressure limit switch you will want to install one to avoid damaging the compressor or even worse, exploding one of your lines or the tank itself.

Click to expand...

10-4 on using all three wires for the positive feed. I'm honestly not sure what the connection at the compressor looks like though as there is just one 12-10g wire coming from it for positive and also one for ground.

10-4 on putting the fuse in the engine compartment, thats what I had planned already for ease of replacement, as well.

see my plan above for a pressure switch. I don't think the compressor has one internally...

i would run this relay...i have 2 of them for my dakota (one per compressor)http://www.hifisoundconnection.com/...fp/SFV/30046/vpid/1333955/vpcsid/0/rid/123284

make sure u run a water trap
http://www.suicidedoors.com/air-management/inline-oilers/smc-inline-compressor-oiler-38


i do not run a pressure switch, i have around 150-200 psi in my tank most of the time...i keep my eye on the gauge.
im not sure if these pics will help you...but what the hell

SanDiegoOverland said:

I'm not planning on running a tank at this time, and was thinking of putting a pressure switch in-line between the compressor and the hose quck-disconnect fitting.

Will that be sufficient for now?

You guys bring up some good points, I think I'll research some of the installs on the board a bit more and probably come back with some more questions...

Click to expand...

An in-line switch should be OK, although I would think it will kick on and off a lot. Maybe not, though...maybe someone running lines only will post up what they've experienced with that set up.

Dude, that's badass. What length is your wheelbase?

I really don't think you need to worry about a relay or a pressure switch on that compressor. All the ones I've ever seen with an on/off switch actually built into the compressor need only a fused 12V+ and ground. Shoot, most of them just plug into a cigarette lighter outlet. Don't know what brand you have, but here is the suggested wiring diagram for hard wiring a Viair 450H (H meaning it has a built in switch).

http://www.viaircorp.com/OffRoad/Schematics/singleh_wd.pdf

I'd install a relay only if for some reason you want to leave the switch in the "on" position and control your compressor with a remote switch mounted by the driver's seat somewhere. How exactly you wire it is really all going to depend on how you plan on using your compressor.

Pulling more than 15 amps from the cigarette lighter is a guaranteed way of producing a large pile of nice pretty burned out blue fuses.

kastein said:

Pulling more than 15 amps from the cigarette lighter is a guaranteed way of producing a large pile of nice pretty burned out blue fuses.

Click to expand...

no worries there, I already have my inline 30amp fuse ready. i'm thinking of stepping up to a 10g wire, though, to keep everything running cool and happy.

I asked above, but didn't get an answer that I can see:

It was suggested that I use all three wires of the heavy duty 12g cable I have(instead of a heavier gauge wire). How would I connect to the single wire coming from the compressor?

However you can - I'd use a wire nut if I was lazy and/or home depot was closed, otherwise I'd probably use a yellow butt splice terminal (12-10awg) - you can get up to an 8awg wire into those and it'll work fine, and I know I've put at least 3 or 4 12awg stranded wires tightly twisted together into one end of one before.

kastein said:

However you can - I'd use a wire nut if I was lazy and/or home depot was closed, otherwise I'd probably use a yellow butt splice terminal (12-10awg) - you can get up to an 8awg wire into those and it'll work fine, and I know I've put at least 3 or 4 12awg stranded wires tightly twisted together into one end of one before.

Click to expand...

10-4.

I was starting to wonder if it was that easy..haha!..thanks:wave:

kastein said:

Pulling more than 15 amps from the cigarette lighter is a guaranteed way of producing a large pile of nice pretty burned out blue fuses.

Click to expand...

OK, so only the really cheesy (low amperage, low air volume) compressors use the cigarette lighter outlet. Most of the ones I've seen with an on/off switch built into them have been of this of this variety. The nicer ones usually have battery terminal clamps.

Regardless, the point I was trying to make was not that he should plug his compressor into his cigarette lighter plug. Simply that extra wiring involving pressure switches and relays is typically not necessary for a compressor with an on/off switch. This applies whether your compressor was supplied with a cigarette lighter plug, with battery terminal clips, or if it a hardwired model... so long as it has a built in on/off switch.

SanDiegoOverland said:

The PO of our house is a good friend and left some electrical supplies, which include several 6-10ft lengths of power cord (some with plugs, some without, that were leftovers from repairing various power tools/appliances, etc.).

These look to be about 12guage with three wires(I'd only use two). They're still wrapped in their protective sheath and are in really good shape.

anyone see any issue with me running this type of wire/bundle from the compressor up to the engine compartment (probably just to the battery itself) for my power supply? I'm going to run it as cleanly as possible, either along the door sills or along the headliner.

Click to expand...

As for the wiring, if you really need to save a few bucks, go ahead and cobble together your short lengths of power cord. I personally would go out and buy yourself a single piece of heavier gauge wire. It shouldn't cost that much if you buy just the length you need. The problem is that there's just not that much room in your door sill trim pieces. A 12/3 power cord is pretty thick once you factor in the insulators for the three individual wires, in addition to the outer sheath, not to mention the extra bulk where you make your splices. You can probably make it fit, but down the road when you want to add other electronic goodies (CB antenna, power wire for an amp, etc.) you're going to find yourself running short on space.

fyrfytr1717 said:

OK, so only the really cheesy (low amperage, low air volume) compressors use the cigarette lighter outlet. Most of the ones I've seen with an on/off switch built into them have been of this of this variety. The nicer ones usually have battery terminal clamps.

Regardless, the point I was trying to make was not that he should plug his compressor into his cigarette lighter plug. Simply that extra wiring involving pressure switches and relays is typically not necessary for a compressor with an on/off switch. This applies whether your compressor was supplied with a cigarette lighter plug, with battery terminal clips, or if it a hardwired model... so long as it has a built in on/off switch.

Click to expand...

Ah, sorry about that, misunderstood what you were getting at.

fyrfytr1717 said:

As for the wiring, if you really need to save a few bucks, go ahead and cobble together your short lengths of power cord. I personally would go out and buy yourself a single piece of heavier gauge wire. It shouldn't cost that much if you buy just the length you need. The problem is that there's just not that much room in your door sill trim pieces. A 12/3 power cord is pretty thick once you factor in the insulators for the three individual wires, in addition to the outer sheath, not to mention the extra bulk where you make your splices. You can probably make it fit, but down the road when you want to add other electronic goodies (CB antenna, power wire for an amp, etc.) you're going to find yourself running short on space.

Click to expand...

Also a very good point. Personally I'd get a single run of #8 cable, which is good up to 73 amps (for short, chassis-cooled wiring - national electric code specifies max current of 40 amps, I believe.) Even with 20 feet of wire @ 73 amps, you will have a cable resistance of 13 milliohms and a voltage drop of less than a volt, with about 10-15 feet and 30 amp load you'll get more like a quarter volt of loss. Neither will affect your compressor in the least, and this will leave you a lot more growing room both in terms of current capacity and space left under your trim for other wiring.

fyrfytr1717 said:

As for the wiring, if you really need to save a few bucks, go ahead and cobble together your short lengths of power cord. I personally would go out and buy yourself a single piece of heavier gauge wire. It shouldn't cost that much if you buy just the length you need. The problem is that there's just not that much room in your door sill trim pieces. A 12/3 power cord is pretty thick once you factor in the insulators for the three individual wires, in addition to the outer sheath, not to mention the extra bulk where you make your splices. You can probably make it fit, but down the road when you want to add other electronic goodies (CB antenna, power wire for an amp, etc.) you're going to find yourself running short on space.

Click to expand...

This is great advice, but I must have mis-stated. I have a supply of new power cable. They're traditionally used for power cords. The lengths are LONG, 6ft being the shortest, 10-15ft being the longest.

This would be one long 3 wire, 12g bundle, about .5" in diameter. Not several smaller lengths spliced...

my fault for being unclear, sorry.

DeftwillP said:

Dude, that's badass. What length is your wheelbase?

Click to expand...

X2!! More specs on the Dak.

SanDiegoOverland said:

This is great advice, but I must have mis-stated. I have a supply of new power cable. They're traditionally used for power cords. The lengths are LONG, 6ft being the shortest, 10-15ft being the longest.

This would be one long 3 wire, 12g bundle, about .5" in diameter. Not several smaller lengths spliced...

my fault for being unclear, sorry.

Click to expand...

Just test your setup before putting in the jeep.
If the wire gets hot, run six "wires" instead of three.

dennis461 said:

Just test your setup before putting in the jeep.
If the wire gets hot, run six "wires" instead of three.

Click to expand...

good idea!

dennis461 said:

Just test your setup before putting in the jeep.
If the wire gets hot, run six "wires" instead of three.

Click to expand...

Now this thread is just starting to get silly... I think Kastein provided some pretty darn accurate numbers regarding the current carrying capacity of the wiring options that have been previously suggested.

kastein said:

I would strongly suggest using all 3 conductors of that cable in parallel as your positive, and grounding the compressor to the unibody - 12 gauge is only going to handle up to about 20 amps, with the motor drawing 30 it is going to warm up significantly. With all 3 in parallel you have a maximum load of around 60 amps, which leaves plenty of headroom.

Click to expand...

kastein said:

Personally I'd get a single run of #8 cable, which is good up to 73 amps (for short, chassis-cooled wiring - national electric code specifies max current of 40 amps, I believe.) Even with 20 feet of wire @ 73 amps, you will have a cable resistance of 13 milliohms and a voltage drop of less than a volt, with about 10-15 feet and 30 amp load you'll get more like a quarter volt of loss. Neither will affect your compressor in the least, and this will leave you a lot more growing room both in terms of current capacity and space left under your trim for other wiring.

Click to expand...

If neither the 60 amps of the 12/3 "power cord" nor the 73 amps of the #8 cable is enough for his compressor, it's probably too big be run as an "On Board Air" compressor in the first place. I still vote for a single, heavier gauge cable for space saving reasons...

SDOverland, just to take some of the guesswork out of this thread, how about telling us what brand/model of compressor you are using?