Relay question - need help

[colton_m]

Hey guys,

 

I bought another led light bar, I have no problems getting it to work. I'd like some help understanding how the wiring harness works. It hooks to the truck battery and has a toggle switch that activates a relay to turn on the light. As far as I know the point of a relay is to supply more power to a device than the activation switch can handle. This makes sense, however, in this case the switch that activates the relay uses the same 12v the relay in turn sends to my light. So my question is why did they even put a relay on this harness if the voltage is all the same?

 

Hopefully someone can explain this is newbie terms.

 

Thanks.

[austingta]

Hey guys,

 

I bought another led light bar, I have no problems getting it to work. I'd like some help understanding how the wiring harness works. It hooks to the truck battery and has a toggle switch that activates a relay to turn on the light. As far as I know the point of a relay is to supply more power to a device than the activation switch can handle. This makes sense, however, in this case the switch that activates the relay uses the same 12v the relay in turn sends to my light. So my question is why did they even put a relay on this harness if the voltage is all the same?

 

Hopefully someone can explain this is newbie terms.

 

Thanks.

This should help.

 

[url=http://s2.photobucket.com/user/austingta/media/threepostrelay_zpsf85bde43.jpg.html][/u

 

RL]They all work like this.

[kstruckcountry]

Same voltage, different current.

[8.1HD/ALLISON]

+1. Its a 12 volt circuit, however the amperage is what gets the work done. By using a relay you can run small wires into the cab for the switch, and the larger current carrying wires stay under the hood. Also get by with a smaller, cheaper switch. Make sence? If you compare electricty to a water supply, you have a garden hose supplying the switch, but it would be like a fire hose supplying the light bar. Electricity can be confusing because you can't see it. Hope this helps. If not let me know.

[Spurshot]

Hey guys,

 

I bought another led light bar, I have no problems getting it to work. I'd like some help understanding how the wiring harness works. It hooks to the truck battery and has a toggle switch that activates a relay to turn on the light. As far as I know the point of a relay is to supply more power to a device than the activation switch can handle. This makes sense, however, in this case the switch that activates the relay uses the same 12v the relay in turn sends to my light. So my question is why did they even put a relay on this harness if the voltage is all the same?

 

Hopefully someone can explain this is newbie terms.

 

Thanks.

 

A classic simple explanation of voltage and current, is the water pipe analogy. Electrical current is akin to how big a water pipe is. Electrical voltage is akin to how fast the water is flowing in a pipe, regardless of the size of the pipe. And as you know, the longer the distance, the higher the resistance, therefor needing an increase in wire gauge to conduct the same amount of current over the longer distance. The whole concept of a relay is to be able to provide more current (amperes) to a device, in the shortest wire run, while using a smaller signal wire that may have to run a longer distance to a switch.

 

A relay is just an electrically controlled switch.

 

For our applications, certainly there are switches that can handle the current needed for running a light. But running high current wires all around exposes them to potential shorts and the extra wire length increases the gauge requirements.

 

Using a relay allows a small gauge wire, low current draw and small switch to run a high current device, such as a huge light bar.

 

The HID harnesses allow the use of the factory headlight wiring to trigger a relay. The headlight wiring only has to power the relay (very low current required). The relay has a larger wire feeding from the battery, which is switched by the headlight signal to provide high current to the HID ballast and igniter.

 

To further illustrate the use of a relay, think about a car's ignition switch and the starter. The starter needs a boat load of current to crank your engine. That current can't go thru a small wire. It would turn a small wire glowing hot and probably melt the wire itself (that's how a lightbulb works). So, a large cable is needed from the battery to the starter (and the same on the ground side, but that is usually thru the chassis). But you need to control it. So you put a relay in between the starter and the battery. The ignition switch and little wires simply trip the relay.

[colton_m]

Thanks guys, that really clears things up. It just looked confusing to me becauee in the case of my light bar wiring they used the same gage wire for everything. I guess the small switch doesn't technically need it but it's easy for manufacture.