12v relay wiring help

[Salf100]

Hi folks. I have two questions.

1. I’m converting my on-board air compressor to a mobile unit and not sure how to wire up the 4 post relay and switch to power. Everything I found online talks about hard mounting the unit, but my plan is to run the power through jumper style cables and mounting it in a pelican case. Using the attached photo as an example do I connect wire one and two together as a single ground and then wire three and four together as a single power lead?

2. Can you use a 24 V circuit breaker fuse on a 12 V system? instead of using a 40 amp blade maxi fuse on my conversion I have a 50 amp resettable fuse that I’d like to use if I can but it’s 24VDC.

 

[racecougar]

1. You could.
2. What is the amp draw of the compressor? What size wire will you be utilizing to power it?

 

[Walkers]

When using jumper wires you don't need a relay as long as your switch is rated for the amp draw.

 

[exranger06]

Wire 1 and 2 both connect to ground/negative battery terminal. Ultimately they're going to be connected together and they're going to the same place. How you connect them together is up to you. You can run separate wires to the negative battery terminal, or you can splice the 2 wires together and run a single wire to the battery. However you want to do it.

Wires 3 and 4 are basically the same: you can run separate wires, or splice them together. However, the fuse must be sized appropriately for the wire. The 50A breaker is fine for protecting the large power wire to the compressor (assuming you're using the correct size wire that can handle 50A), but presumably you're going to run a smaller wire to the switch, which can't handle 50A. So wherever the small wire branches off from the big wire, you need an additional fuse/breaker that's sized appropriately for the small wire. If you run a separate wire from the switch right to battery positive, the fuse/breaker should be as close to the battery as possible.

And yes, a 24v breaker will work fine on a 12v system.

 

[wyliesdiesels]

The fuse needs to be sized to the wire. You dont want oversized fuse as your wire could melt on overload

What size wire are you using?

 

[Zeke]

I would run the 2 battery jumpers out of the Pelican and mount the switch and relay in the case. The has nothing to do with running the compressor in an open or closed case. You know what to do there. So the switch can be inside or mounted for exterior use.

Inside the case wire as it is and take a fused tap off the + terminal through an appropriate sized fuse to one side of the switch. All it does is provide a low current to the relay to close. No ground needed at the switch.

I've only repeated what has been said already with some ideas to simplify the connecting cables. You only need the 2 cables going to the battery to be loose and you can poke thru the case or coil and store them in the case. I'd buy the best cables there are or use welding cable. To size the main fuse you have to know the compressor rating. 50A resettable breaker won't protect a motor that needs 40A protection, no matter what wire as long as it's large enough for the length you plan.

 

[Zeke]

duplicate post

 

[Salf100]

Ok thanks for everyone’s reply’s. The compressor has a 14 amp draw at no load and 32.2 at full load and my plan was to wire everything with 10 gauge cable. 10 gauge because that’s the size of the +/- cables coming off the compressor. Also when it was hard mounted in my truck it was fitted with a 40 amp maxi fuse.

 

[Zeke]

10 ga. is gonna be marginal and could get hot. It might work, depends on usage. Me, I'd go at least #8 for less than 15 feet. 6 for longer.

 

[racecougar]

I would recommend increasing the wire size and maintaining over-current protection at 40A. What series wire are you using and what length are your leads?

 

[Salf100]

Got it. Keep it at 40amp fuse. I haven’t purchased the wire or clamps yet, so if anyone has a good source for those please let me know. All the original wiring that came with the on board kit was 10 gauge, but I failed to retain any of it when I got rid of the truck. Can I wire the switch, relay and connection to the compressor with 10 gauge and use larger wire for what I run to the the battery? The plan was to keep the power wires no longer than 6 feet.

 

[rockettauto]

Got it. Keep it at 40amp fuse. I haven’t purchased the wire or clamps yet, so if anyone has a good source for those please let me know. All the original wiring that came with the on board kit was 10 gauge, but I failed to retain any of it when I got rid of the truck. Can I wire the switch, relay and connection to the compressor with 10 gauge and use larger wire for what I run to the the battery? The plan was to keep the power wires no longer than 6 feet.

You can, if your already sizing the main fuse for 10ga....otherwise when you branch off with smaller wire you add inline fuses.

 

[walta]

Tell us about the relay you are planning on using.

Compressors are notoriously hard to get started I would want a relay much higher than motors rating maybe 2 or 3 times.

Something like the one in this link.

Relay 12V / 75 Amp Dual Diode

www.egismobile.com

Note the green wires in this drawing could be very thin like #22 but the black wires should be thick like #8.





Walta

 

[Salf100]

Manufacture recommendations is a 40 amp, 4 pin Bosch style relay. That’s what I ran it with for 5 years with never an issue. It’s a small ARB single compressor that puts out 3 CFM.

 

[fitter30]

Hope the compressor has unloading at startup.

 

[Zeke]

He seemed to say he was using all of the stock components as used in the truck. That's why I said keep it as it is and add new flexible leads like good quality battery cables. The OP seems to have missed that.

 

[Salf100]

Unfortunately I failed to keep the original wiring harness to make my life easier. Essentially I’m trying to build a new harness just a smaller scale that will fit into a hard case.

 

[Salf100]

I found this from the manufacturer web site. This may help.

 

[theoldwizard1]

Standard automotive fuses can pass the rated current for MANY MINUTES before blowing. Very little difference between fuse rated for anything between 12VDC - 48VDC. It is current that cause the heat, melts wiring and blows fuses !