Air compressor

[Johnkathy81]

Just after a little advice on wiring my air compressor in my tub. Have wired my light bar, spotlights etc.. So have little knowledge with relays fuses etc.. Just needing to know what gauge power wire I should run to be sufficient to the tub? Will just be for pumping tyres.

Thanks.

 

[Carchania]

G'day mate.

What compressor did u get? I bought the thumper just recently based on what people have said on here and that came with really quite thick cable with alligator clips on. Also just put my secondary battery in tray on other side of toolbox and the cables were long enough I can cut the clips off and permanently connect to the fuse panel I put in there. I'd say the cable is nearly as thick as the battery cable in the engine bay. So it must pull some decent amperage. Just gotta wire up my switch to the pressure solenoid on the tank or to a switch in the cab. Haven't decided yet. What r u going to use to turn urs off and on?

 

[Johnkathy81]

Hey mate, Yeah that's my whole thing I'm trying to work out at the moment. I have a supercheap one I bought few years back I will use just for now then change when it blows. Therefore was thinking of wiring it to a Anderson plug. Will be wiring to a a incab switch regardless but also trying to figure out how pressure switches work. Also well I'm running wire to it in the tub., What thickness cable I should run from the start incase I maybe run something else off there also.

 

[bods]

If you're running cable to the tub, get the thickest you can. I've run 50a rated 6mm (4.59mm2) cable in mine, which is enough for what I'll be using it for, but it depends what you are going to be running from the tub. Also, if you're going to have another battery in there and how you're going to charge it. That size will be sufficient for a dc-dc charger on an aux battery in the tub if you decide to go that way in the future.

An anderson plug will be fine for that compressor. I have one of the thumper type ones from supercheap and I'm pretty sure it has a 40a fuse on it, so that gives you an idea of the power it will draw. Pressure switches are only needed if you have a tank in there that you want to use to help the compressor by holding air to start with. It will just cut the compressor out when it reaches its pressure so it doesn't blow up...

 

[Johnkathy81]

If you're running cable to the tub, get the thickest you can. I've run 50a rated 6mm (4.59mm2) cable in mine, which is enough for what I'll be using it for, but it depends what you are going to be running from the tub. Also, if you're going to have another battery in there and how you're going to charge it. That size will be sufficient for a dc-dc charger on an aux battery in the tub if you decide to go that way in the future.

An anderson plug will be fine for that compressor. I have one of the thumper type ones from supercheap and I'm pretty sure it has a 40a fuse on it, so that gives you an idea of the power it will draw. Pressure switches are only needed if you have a tank in there that you want to use to help the compressor by holding air to start with. It will just cut the compressor out when it reaches its pressure so it doesn't blow up...

Thanks mate won't be using a air tank so wont bother with that then. Sick of running cables all the time so will run what you recommend and at least I know for future if I was to run a second battery etc.. It will be ok. Do you recommend I run earth also direct from battery from the start or just to good chassis ground?

 

[Johnkathy81]

Also if I was to run a cigarette (auxiliary) output at the rear near compressor how would I go about that? Can I just loop from that wire and maybe put a fuse? Thanks.

 

[bods]

Personally, I only ran the earth to the chassis under the tub, but it is recommended to run to the front battery. In saying that, I've had it that way for a couple of years now without issue. I used to run my old compressor off that wiring, but I have got some 50a anderson plugs coming so i can wire the new one up the same way. Saves having to open the bonnet every time. I will just put a switch in the tub hooked up to a relay to supply power to the anderson plug in the car. No point trying to run extra wiring from inside the cab and I don't have any spots for more switches anyway lol.

Just one thing to keep in mind with the cable, they do a single core version, which is what i used, but they also do a twin core (both in the one outside sheath) which isn't rated at 50a, because of the heat generated when it is in use. Apparently the twin core version is only rated at 38a.

 

[Johnkathy81]

Thanks for your help mate might just run two separate cables to be safe. So with running the switch though and the relay being under the bonnet I would have to run a wire either to the tub or incab regardless wouldn't I to activate the relay?

 

[bods]

Depends where you want to put it. Mine's going in the tub with the wiring and the switch. When it's all sorted I will have a mini power distribution box with all relays, etc in the tub. I have a 50a circuit breaker under the bonnet on the feed to the tub. Just want switches on the anderson plugs to isolate them when they're not in use. The switch will just use power from the aux battery to trigger the relay.

 

[Johnkathy81]

Thanks mate I had just thought that the relay had to be under the bonnet near battery. Sorry for the 1000 questions mate just trying to do it right from the start. What's the difference with a circuit breaker and a inline fuse as I have never used them? Also to make sure I'm onm the right path I'll run wiring direct from battery via circuit breaker to tub. From in tub run that wire to say a fuse box (not sure if that's what you were referring to when you said power distribution box?) Then from that I can run my relays and switches from of that?

 

[happy john]

Hi John, a circuit breaker can be manually reset whereas an inline fuse if it blows needs to be replaced. Here is the wire that you need.
http://www.rapidcables.com.au/twin-6-b-s-starter/
John

 

[Johnkathy81]

Thanks for your help mate.

 

[bods]

Thanks mate I had just thought that the relay had to be under the bonnet near battery. Sorry for the 1000 questions mate just trying to do it right from the start. What's the difference with a circuit breaker and a inline fuse as I have never used them? Also to make sure I'm onm the right path I'll run wiring direct from battery via circuit breaker to tub. From in tub run that wire to say a fuse box (not sure if that's what you were referring to when you said power distribution box?) Then from that I can run my relays and switches from of that?

Yep, that's correct. I will have other power sockets and stuff there too, that's the only reason I said distribution box, but you are on the right track

 

[Panuara]

Earth

Personally, I only ran the earth to the chassis under the tub, but it is recommended to run to the front battery. In saying that, I've had it that way for a couple of years now without issue. I used to run my old compressor off that wiring, but I have got some 50a anderson plugs coming so i can wire the new one up the same way. Saves having to open the bonnet every time. I will just put a switch in the tub hooked up to a relay to supply power to the anderson plug in the car. No point trying to run extra wiring from inside the cab and I don't have any spots for more switches anyway lol.

Just one thing to keep in mind with the cable, they do a single core version, which is what i used, but they also do a twin core (both in the one outside sheath) which isn't rated at 50a, because of the heat generated when it is in use. Apparently the twin core version is only rated at 38a.

Nearly cooked my Nav when battery case let go and battery moved and hit tub, dead short through earth back to main battery, burnt out wiring harness, lucky not to lose house as well. Auto elec said either put fuse in earth return to main battery or use a short length of heavy cable to chassis . This is preferred method.

 

[Carchania]

G'day
The place I bought my cable from to run to the second battery said I should avoid earthing it straight to the chassis and instead earth back to the battery. I think old tony stated why in a post not so long ago. I didn't realise should run an inline fuse on the earth. What size did the sparky recommend mate?

 

[Old.Tony]

If you fuse the positive line there's little need to fuse the negative.

The rule of thumb is: if you're running a cable anywhere there's a risk of damage, put a fuse close to the power source.

Run a cable from front to a charger in the rear: fuse at the front
Run a cable from front directly to battery in the rear: fuse both front and back
Run a cable from AUX1 to AUX2 in the back (sitting beside each other): NO fuse
Run a cable from front to a trailer connection at the rear: fuse at the front

That's the general idea.

Separate earth: that's to avoid chassis grounding connection issues. Particularly between tub and chassis - the electrical connection may not be reliable or might become unreliable, which will compromise your battery system.

Just as an observation on different cables: single strand (like house wire) is really bad for cars, because cars are in motion and houses (unless you're in Newcastle) generally aren't. Multistrand wire is recommended. Having an inner and outer conductor - like the old network cabling or current TV antenna cable - is a very nice idea, but can suffer from crush damage really easily. Whereas a pair of cables lying beside each other might avoid contacting each other through crush damage, you can pretty much provide a written guarantee that the inner-outer cable will be destroyed when crushed.

 

[bods]

The only thing I can think of that caused the above issue is, because the earth went back to the engine bay, that whole run of cable let power through when the battery shorted out on the tub. Obviously, had it happened in the engine bay, there are very short runs of cable, so if somehow the battery hit the bonnet and blew all the fuses between it and the cars wiring, but continued to short out then there is only a short run of negative cable to burn out... with the above scenario, there is the same length of negative cable as positive, so if only the positive terminal of the battery contacted the tub and blew the fuses or breakers, then the power returning to complete the short circuit would travel all the way back to the only earth point, being the front of the vehicle.

Does that make sense?

Maybe it is worth putting a breaker or fuse of the same rating as the positive side on the negative side of an auxiliary battery mounted in the tub, if running the earth all the way back to the main battery?

 

[Johnkathy81]

Thanks for all the input I havnt yet run any wiring but got it all yesterday and just started building my draws today, that will be used for work and camping, canopy to follow so I can ditch the work trailer when not needed. Not planing on running a second battery at this stage but got some twin core narva wire think it was about 6mm 50amp rated and a circuit breaker 50 amp to put near battery and run all to a fuse box in tub. From there run my compressor via relay and a switch, and whatever else required. When I do run the earth to the tub can I just crimp all my earth's together there, compressor, Aux, relay earth's etc..? Or is there another way? Thanks.

 

[bods]

Depends what you want to do for fuses. At the moment i have 2 bus bars set up in mine, 1 for positive and one for negative. The positive goes into the bus bar, then out to a basic fuse box, the from the fuse to the socket. The negative just goes back to the negative bus bar.

You can get fuse panels that have positive and negative all going through the panel though. Narva and baintech both do them I believe. I am considering getting a narva 12 outlet one, just trying to work out if i will need that many circuits or not. They are on ebay for 43 bucks, is the cheapest I've found so far... then you just hook the earths from the devices into the fuse panel and hook that up to the new power wiring.

 

[Old.Tony]

The only thing I can think of that caused the above issue is, because the earth went back to the engine bay, that whole run of cable let power through when the battery shorted out on the tub. Obviously, had it happened in the engine bay, there are very short runs of cable, so if somehow the battery hit the bonnet and blew all the fuses between it and the cars wiring, but continued to short out then there is only a short run of negative cable to burn out... with the above scenario, there is the same length of negative cable as positive, so if only the positive terminal of the battery contacted the tub and blew the fuses or breakers, then the power returning to complete the short circuit would travel all the way back to the only earth point, being the front of the vehicle.

Does that make sense?

Maybe it is worth putting a breaker or fuse of the same rating as the positive side on the negative side of an auxiliary battery mounted in the tub, if running the earth all the way back to the main battery?

That's the thing about negative - you can just lump all of them together, connect them any way you like, because even 100 batteries with their negative poles connected together won't form a circuit. It's only when the positive side gets connected as well that things start to happen, so for simplicity's sake, automotive convention is to earth (ground, connect, whatever term you choose) the negative side and forget about it.

Even running a whole negative cable to the rear - the only thing you're really achieving by doing it is reliability. You aren't actually changing the risks. Snag a negative cable on a stick so that its insulation breaks and rubs against the chassis will do nothing at all. No power will flow, no cables will heat up, no fires will be started, no sparks - nothing.

Snagging the positive cable is something else - because (by modern convention) cars are earth-negative, the positive cable DOES represent a risk when run anywhere, so my advice to everyone remains: connect negative any way you like, and whack a fuse close to the source of power on any cable run that could be damaged.