Hi just have a quick question about some offroad lighting. i know how to hook them up and using a 40A relay. My question is what gauge wire to use from battery and to the lights? I was thinking 14 gauge? Or am I going to have to go with something bigger like 10?
Thanks for your help
Daniel

 

14 gauge should be fine but 12 just a bit better.

Use good weather tight connections and shrink wrap---I'm sure you already know about this though!

 

Thanks for the reply I'll get some 12 gauge wire.
Yeah i solder and heat shrink all my connections. I dont like crimping.
I want to make the lights where if i want to take them off for any reason I can just unplug them from the main wiring. Any ideas for a good weathertight plug to use that I should be able to get locally?

Thanks for your help,
Daniel

 

520W is over 40 amps at 12 volts. Neither a 40 amp relay nor 12-gauge wire will safely handle that if you're trying to run the entire circuit at once. I assume 520W is from more than one light, in which case you'll want to split up the relays and wiring.

 

If you check with online or local trailer service, RV or marine outfits they're likely to have something suitable. Cole-Hersee as a brand tends to have very stout devices in general too. I'm sure there are other brands and types available as well.

 

yeah 520W is four 130W lights that I want to run on one switch. So I guess thats gonna be almost 44 amps. If I run 2 relays how would I hook up the second relay in the same circuit? I've never hooked up two relays in one circuit before just one. And if I use like two 30A relays what size wire should I run for each relay? Would 12 gauge be enough for each cause that would be splitting the 44 amps into 22 amps each right?
Thanks for your help,
daniel

 

12 gauge would be enough per relay per 2 lights. Hook directly to the battery with two 12 gauge wires that run a very short distance to some sort of fuse box or inline fuse. You will have 2 fuses, I would run 25 or 30 amp fuses for each.

After the fuses you can run any distance you like(since these wires will be protected by each fuse) to the relays. Each wire will go to it's own relay, and then there will be another 12 gauge wire leaving each relay going up to feed 2 lights each.

The coils for the relays will be tied together. The easiest way is to jump one side of each coil together, and hook a small jumper from this to one of the power wires coming from the fuses.

Jump the other side of the coils together, and then hook a wire to this and run it into the cab to a switch. Hook this wire to one side of the switch, and hook the other side of the switch to a good ground.

If you want to use a lighted switch, you will have to hook this up differently.

 

Thanks dave Im gonna add a second relay to it and another fuse and get some more 12 gauge wire. Hopefully will get some time to work on it in next couple days.
Daniel

 

12 ga is insufficient for two 130W lamps in parallel. Maximum ampacity for 12 ga copper is 20A.

Either bump up to a 10 ga or wire each light individually. If you use individual wires for each light, 14 ga is fine.

If you were to wire all four lights via one circuit, you'd need 6 ga to safely handle the current.

 

130 x 2 = 260w 260w divided by 12v = 21.67 amps. I believe that is close enough to work ok, 20 amp capacity for 12 gauge is the spec for house wiring, and if you follow the example of how Ford sized it's wire, it should be good. But I am not against running larger wire, especially if the cost is not that much greater.

 

The 12 gauge wire I got from advanced auto says on the back for one 12 foot length of wire it can handle 26 amps.

Now how about the grounds? Do I need a heavier gauge wire for the grounds of the relays or is a smaller gauge ok for that? And also how about the grounds for the lights themselves?

 

The coils are the only part of the relays that need grounds, and this wiring to the dash switch(if you wire it that way) can be very small, you do not have to run the 12 gauge inside the cab for the switch. That's the whole purpose of the relays, their contacts handle the high current, but they are controlled by a small cheap switch and small wiring.

Your grounds to the lights should be 12 gauge. Most lights ground through the housings unless they are plastic. The sheetmetal and frame of the truck should be adequate for the ground unless you have a lot of rust. Just go through the ground path in your mind, and if for example your large factory ground wire has been changed and no longer is attached to the frame, you can run a couple of 12 gauge wires from the battery negative to the frame to give the frame a good ground and a good return path for the lights. If your body mounts are rusty, you can run a short ground wire from the frame to the bar that mounts the lights.

 

Just a thought, the voltage you ought to be designing for is more like 13 volts. If the bulb is a halogen, the higher voltages will make it recycle the filament back onto itself. It will last longer with this higher voltage. Also, the light output is exponential. So a little more juice gives it a lot more light. You wouldn't be getting only 12 Volts unless your wiring is restrictive, or the alternator is not keeping up.

Remember, it takes over 13v to charge the battery well. The new cars tend to run at about 13.8 - 14.2v. Not all of that gets to the bulbs of course. There is normally some resistance there.

With everything running, you shouldn't have more than a 0.5v drop between the alternator output to the back of the highbeam socket. Look for resistance on the way back to the negative battery post, also. (OFF when using resistance on the meter...) The vehicles I checked all had restrictive grounds and wiring. This is for the headlight circuit only I believe.

Don't make all wires bigger for no reason. Some of the other circuits need the restriction of a smaller wire. Small wire can reduce current, surges to some extent, and have a lesser arching danger in event of collision.

 

It should, unless there is excessive resistance in the supply circuit

The alternator is connected to the positive post of the battery. There should be no voltage drop between the alternator and the battery's positive post.

No such thing. All circuits expect to receive full battery voltage at all times. The wire size for any given circuit is determined by the estimated current draw of the circuit when compared with the ampacity of the different wire sizes.