42 in 120w led lightbar fuse

Put in a 42 in light bar and wired it to an auxbeam 8 panel box. The light is 40 3 watt lights so 120 w total. According to the math I was taught it’s watts/volts = fuse size so 120w/12 volts would be a 10 amp fuse. I used 14awg wiring as well. The fuse keeps popping. I moved up to a 15 amp fuse and it seems to be fine. Should I have any concerns with a 15 amp fuse? Thank you and merry Christmas

 

Do you have a clamp on amp meter that you can use to double check? Math looks right, how long of a run is the wire? Are you working off a relay or a switch, Not familiar with that exact panel box.

 

Make sure you use a relay. Most switches are rated for a very small load.

 

The fuse is intended to protect the wiring from catching on fire in case of a short, not the load. According to this Bluesea chart, 15 amp fuse is acceptable for 14 awg wiring up to 20 ft: http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg

 

120W on a 42” light bar seems low. Have a link to the bar?

 

^Well it keeps blowing 10A fuses but works with 15A fuses, so we know it's drawing somewhere between 120W and 180W

 

Thanks everyone. Here is an update. So the auxbeam “control module” has a relay and slots for fuses. I mounted it on the drivers side fender towards the firewall. So the wiring run is maybe 4 feet. Literally out of the hood, up the side of windshield and to the light bar on the crestone roof rack. Here is the crazy part. I emailed the lightbar manufacturer and they said to use a 20 amp fuse. I don’t buy that. I think a 20 amp is too big. I put the 15 in and it appears to be fine. I also have six other lights on the truck that are working flawlessly - each on their own fuse and switch.

 

Good point. My 20" Rigid SR draws 132 watts.

 

So I do have one. Didn’t even think about that. Thank you I’ll go do that

 

There might be a surge at startup. I'd go by what the manufacturer says.

 

There are 40 leds and according to the manufacturer it’s 120 watts. 3 watts per led.

 

20A fuse is also acceptable per the Bluesea chart given the short run. However, the chart is correct only for good quality stranded copper wire. If you are using copper-clad-aluminum wire (as is often found on Amazon), the current capacity is cut by half.

 

One critical piece I left out was a 20 amp fried the led lightbar. Of course it happens in the Florida Everglades on a really remote road. So a 20 amp fried the light bar and a 10 amp popped the fuse. That’s where I thought ok. Maybe a 15 amp is the sweet spot. I just went out and checked it. Working fine.

 

A bigger fuse won't fry the light bar. Fuses don't control how much current a device draws. They just blow when they're overloaded. If the bar failed on a 20 amp fuse, something else was wrong. As @3JOH22A mentioned, the fuse only protects the wiring from being overloaded or in the event of a short.

 

Why so cagey with who manufactured the light bar?

I’ve got a 10” Rigid bar that pulls 98W and a Diode Dynamics 12” bar that pulls 60W. Listing the manufacturer or linking it would help

 

Carry some spare fuses and give it a go. As a previous poster stated, fuses/circuit breakers are intended to protect the wiring, not the device.

 

It is llas

thank you all. And Merry Christmas. This is. Lasfit 42 in LED bar. Yeah I have some spare 10,15,20 fuses.

 

A fuse will only carry 80% of its rating continuously. Your 10 A fuse was too small. The National Electrical Code allows you to fuse for the wire feeding the load. #14 AWG is fine fused at 15 A. That's the max ampacity of #14 AWG wire.

You had the wrong fuse in there @ 10 A for a 10 A load. A 15 A fuse will continuously carry 12 A.

In this engineer's, and 4Runner Aficionado's opinion you are golden... Enjoy!!!

 

Perfect. Thank you!