Led wiring question

[Mowgli]

I'm going to be wiring a 72w 12inch led light bar and and unsure of the wire size along with fuse sizes. I've been hearing I don't need a relay since it is a very low draw.

Does anyone have a wiring diagram for this that includes the wire sizes.

 

[susswein]

72 watts @ 12 volts is 6 amps, so I'd probably use a 10 amp fuse. The wire size you need depends on the length of the run. For a run of up to 15' you could use 14 gauge wire.

http://www.affordable-solar.com/Learning-Center/Solar-Tools/wire-sizing

 

[BrianTN]

At what point is a relay needed?

 

[JamesW]

I would be sticking a relay into that. Otherwise you'll have 6 amps going through a switch,which will get rather hot. Using a relay isn't that hard anyway,and will save you a lot of grief.

Personally i'd use a relay on anything more than 16ish watt. Otherwise you end up trying to suck extra current down the factory wiring,which can cause trouble

 

[Hilldweller]

A good relay and 12 gauge can save you some grief in the future.

Who told you that 72 watts is a low draw? I guess it's relative but I always err on the side of caution when it comes to juice.

 

[Mowgli]

I would be sticking a relay into that. Otherwise you'll have 6 amps going through a switch,which will get rather hot. Using a relay isn't that hard anyway,and will save you a lot of grief.

Personally i'd use a relay on anything more than 16ish watt. Otherwise you end up trying to suck extra current down the factory wiring,which can cause trouble

I won't be connecting it to any of the factory wiring. Just strait to the battery

 

[pugslyyy]

Relays really are quite simple. But if it is going to be a switch just make sure it is rated for at least the fuse rating (10 Amp). You want the fuse to blow not the switch to melt.

 

[Mowgli]

So if I use a relay would it still be 14 gauge all the way around?

I'm using a kc 30 amp switch

 

[Mowgli]

Found some good links

Wire size for amp and length

http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm


Calculator for amps

http://www.supercircuits.com/resources/tools/volts-watts-amps-converter

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So for what I'm reading I could use 18 gauge wire (which I'll go 16 or 14 to be safe). I'm pulling 6 amps so I should use the closes fuse to that which is 7.5.
Is that correct?

I got another set of lights which are 18w but I'm wiring them together so does the draw stay 18w or would it double?

 

[Howard70]

...So for what I'm reading I could use 18 gauge wire (which I'll go 16 or 14 to be safe). I'm pulling 6 amps so I should use the closes fuse to that which is 7.5.
Is that correct?

I got another set of lights which are 18w but I'm wiring them together so does the draw stay 18w or would it double?

I'd never use a run of 18 g wire on driving lights. Remember that while the wattage for the lights remains nearly constant, wattage is the product of volts x current (amps). So as the voltage drops the current has to increase to supply the lights with the correct wattage. Turn your lights on without the engine running, and in a short time the battery voltage can get low (especially if other lights are on) the amps can go well above 6 and you'd cook the wire.

Two 18 watt lights use 36 watts. The voltage stays the same and so what has to happen to the current? It increases.

My general rule of thumb is that I always use at least 16 gauge wire on my vehicles unless it's an instrumentation circuit. I also always use tinned marine grade wire. With regular "untinned" copper wire it often gets the green crud. That green crud is copper oxidation and it isn't a good conductor at all. So with green crud the wire's resistance increases and 18 g wire starts to conduct like 22 g wire. Tinned wire doesn't develop green crud so it retains it's conductivity longer.

x2 on all the above comments about relays.

Howard

 

[Mowgli]

Sorry for my horrible ipad drawings. So this is how it would be done without a relay correct? All with 14-16 gauge wire and a 7.5 fuse


With a relay now. Still with 14-16 gauge wire and 7.5 fuse. What I'm confused on now is since only one wire is going to the switch how will the light get lit up on the switch or could I just jump that wire onto the 3rd prong to light it?
Do I still need 14 gauge wire coming from the relay to the switch since it won't be 6amps any more


Thank you for all your help too.

 

[Mowgli]

Anyone?

 

[BigJimCruising]

You still need a hot wire B+ going to the switch then to the relay. So it's really 2 hot wires going to the relay, one is the main power that flows through the relay to your lights. The second hot wire goes to energize the relay to allow the other power to go to the lights.

Don't know how to draw it out but where you have the question mark at the switch should be the wire to the relay, then going to the + side of the switch should be from a power B+ (or battery).

By the way your wiring diagram is for a lighted switch. If the switch isn't lighted then you don't need the ground.

Hope that makes sense, kind of hard to describe! lol.

 

[04gmc]

Mowgli your drawing is pretty close. In order to trigger the relay the switch has to have its own power source. The switch then sends this current to the relay when its "flipped", causing the relay to close, therefore completing the circuit allowing the current from the battery to travel to the lights. And because relays hardly draw any power (typically < 1amp) you could probably get away with using 18awg wire or smaller, but to be safe I would stick with 16awg for all wires running to and from the switch. For everything else use 12 or 14awg.

Also, since your switch is three pronged you don't need to worry about independently wiring the light for it, it will light up automatically when you turn it on. The downside to this type of switch is that it won't light up while its in the off position.

If I were you I would tap into the HVAC or cigarette lighter fuse to power the switch. That way you can only turn the lights on while the engine is on.

 

[cajunrebel]

Most standard automotive switches are rated to about 20 amps at 12 volts. Above that you generally need a relay. KC has a heavier duty switch so that customers with smaller light setups can just use a switch for simplicity's sake. Not everyone knows how to run a relay or even that they need to. I am personally running reversing relay setups to power my windows because the original Ford switches are the weak link and cause slow windows. With the relay setup even my massive rear window goes up as quickly as a new Mercedes window.