How important is a relay for LED light bar?

[CrazyDrei]

I can not seem to find this answer anywhere, but exactly what does the a relay do in a light bar wiring harness?

I have been running a 36" light bar on my truck for 5 years with no problems. It is wired: battery + to inline fuse to light switch on dash to light bar positive cable, negatives are directly grounded to frame. My switch is rated to 40amps. I have been using the light bar for 200-300hrs a year for last years with no problems.

All new light bar wiring harnesses come with a relay, WHY?

Please educate me or point me in the eight direction.

 

[Deleted member 9101]

Don't know...but I'd probably ask the manufacturer before I asked strangers....lol.


Also, not everyone uses a switch when the wire in a light bar. Mine uses a relay, triggered by my highbeams.

 

[Chorky]

Probably mostly depends on how you want it wired, and the amp draw. Like already said if you want it wired into your high beams. Back in the day most halogen lamps (pair) could pull 20 amps easy, for less than half the quality of light of a modern led. But a pair of XL80's from Baha pull 11a. Still more than I personally would want going through a switch... I think most standard switches folks use are rated at 20 a. But that is highly variable. When in doubt, be more cautious. An electrical fire is no fun and an easy way to burn down an expensive vehicle.

 

[tacobronco]

A relay is simply a switch controlled by a switch. Sounds redundant, but the purpose is to isolate the high current under the hood and limit it to as short a wiring run as possible. That way you have less voltage drop, and less risk of the wiring or switch overheating.

True, LEDs require less current than conventional bulbs, but for an entire light bar, I would use a relay. From what I've seen, commercially available LED auxiliary light kits generally include relays, so apparently they agree.

 

[Betarocker]

Certainly you can wire as you did, but you physically need to switch it off and on as needed. Oncoming traffic requires dimming the highs and turning off the light bar, unless you're an @$$ and don't give a ******** if you're blinding them. Chances are if you need the light bar, you'd benefit from the high beams too. Why not trigger the light bar with the high beams?

 

[Chorky]

Which "quality" exactly?

The halogens of the older era (10-20 years ago) can't match a high quality LED output amp for amp.

 

[Deleted member 9101]

Chances are if you need the light bar, you'd benefit from the high beams too. Why not trigger the light bar with the high beams?

That's what I did along with modifying the fog lights in the bumper to stay on with the high beams.... It puts a lot of lumens on the road in front of me...haha.

 

[Chorky]

Oh... yeah LED definitely has higher lumens-per-watt.

A few of them have good pattern too, like the PIAA indirect bars don't seem to be a nexus of glare and hatefulness. Pricey though!

I don't really think CRI is an important quality for driving lights and may even make them harder to live with; but it's more important to see the deer in the road early than it is to know what Pantone shade its beard is and the nature of white LED emitters means they are typically much too strong on blue output which doesn't focus well in our eyes thanks to chromatic aberration and rayleigh scattering.

I get salty about the topic of LEDs for three reasons; one is that people seem to get absolutely obsessive about them for some reason and I find that weird and off-putting, two is that even if very good LED lamps do exist this fact seems to be lost on all the oncoming traffic blinding me wherever I go on and off road with their glare bars, and three a lot of people act like incandescent lighting is equivalent to practicing an Amish lifestyle and LEDs are like living in Star Trek times which just isn't representative of reality at all. Both technologies have their place and quality halogens are a lot better than LED fetishists make them out to be.

Good points, and not to derail from the OP's question, but I think the argument can be certainly made in your favor for the majority of LED's available. But if you consider the high quality companies - vision x and BajaDesigns - then they are clear winners over halogen. I had high quality halogens years ago, and 2 years ago got 2 XL80's. They are by far way better with just 2 of them than 6 halogens. And their color is neutral compared to most lower quality LED's even Rigid. But....thats just my .02. In terms of LED's - if you don't go high quality, then mine as well just stick with halogens - unless amperage is a concern.

 

[GlennA]

If I were running an LED light bar, I would use a relay triggered by the bigh beams . That being said, I would also put a switch on that trigger line to allow me to turn off the LEDs and still use the high beams. It would not allow use if the LEDs without the high beams. Clear as mud.........

 

[CrazyDrei]

Thank you guys. So in short if you do not properly wire the light bar to a battery and use a correct amperage switch which will keep the light bar on it's own independent circuit a relay is unnecessary.

However if you tap into the high beams or another lower voltage switch then you will need a relay to avoid an electrical fire.

Thanks for stirring up the mud, LOL.

 

[drrobinson]

One more thought to consider.
You can use a ground trigger for a relay and thereby avoid having a long run of positive wire through the engine compartment, through the firewall, under the dash.

That way of something chafes the worst thing that happens is the lite bar switches on, rather than a blown fuse or fire.


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[CrazyDrei]

One more thought to consider.
You can use a ground trigger for a relay and thereby avoid having a long run of positive wire through the engine compartment, through the firewall, under the dash.

That way of something chafes the worst thing that happens is the lite bar switches on, rather than a blown fuse or fire.


Sent from my iPad using Tapatalk

Can you explain negative triggers a little more, I'm not finding too much specific or relative info on them?

I already have a power distribution block under the hood that's connected to the battery. From there I run a wire to a circuit breaker and then a power wire into the cab power distribution block. I only had 4 wires running from the engine bay to the cab, but I am upgrading to more lights and want to keep a setup that will not catch my truck on fire. So sounds like as long as I keep using correct amperage switches I don't need a relay for an independent system.

If I decide that I want use lower powered switch from a fuse tap that's on only when ignition is on then I would need a relay. This would be considered a positive trigger right? And this would also ensure that light bar can not be turned on when the truck is off.

I am adding more lights and re-wiring some accessories that I like to be able to keep on when the truck is turned off. So it sounds like I will not need the relays after all as long as my switches are rated to carry the current of the light bar and other accessories.