Fuse Rating Selection

[bds85466]

Greetings,

I'm planning on wiring in some LED rope lights (12V) into the gunwales of my boat. Since I don't have any remaining switches/fuses open, I'm going to wire my own in.

I'm planning on using a max of 18ft of lighting, and the rating is max 0.8W per foot of lights. So the max would be 14.4W ... ~ 15W.

Dusting the cobwebs out from my circuits class, assuming a fixed voltage of 14V, the lights switched on would would draw: 15W/14V = 1.1Amps.

I'm guessing there's not a lot of current surge when you flip on LED's, but I'm trying to figure out which size fuse to utilize. I've heard in general, add 50% or so... 2Amp?, 3Amp?

I suppose that once I get everything set up, the acutal may deviate from the theoretical as well. I plan on metering my battery voltage (12 - 14?) and then also metering the amp draw of the lights on this voltage. All of the above theoretical numbers would be worst case as that's the max wattage, max footage and max voltage.

I'm just trying to figure out what fuse would be sized correctly so you don't keep breaking them and still be safe. Anything I'm wrong on or forgetting? Thanks for any help!

 

[bruceb58]

Re: Fuse Rating Selection

Depends on what you are trying to protect. If its the wire leading up to the lights, you can use a 10A fuse for a 16 guage wire. Basically, whatever is the weakest link in the circuit that you would like to protect. That is why many radios will have a smaller fuse at the end of the power feed. They don't want the radio relying on the 10A feeder circuit to protect it.

No current surge with LEDs.

 

[ajgraz]

Re: Fuse Rating Selection

I've got 6 individual LED's as cabin lights, wired in parallel with 18AWG (could have used 20-22AWG easily, but my runs are kind of long). Altogether they draw less than 200mA. I'm using a 0.5amp fuse. Never had an issue.

I'm thinking a 2 to 3 amp fuse ought to do you.

 

[bds85466]

Re: Fuse Rating Selection

I think i'm getting your drift -- I'm not sure there's anything (hardware) to protect if there's nothing else on the serial circuit(?). Protect against a short and a fire? Obviously the LEDS...

I'm planning on coming off of the main +12 into a [correctly sized] fuse (using 8g), then to a [lit spst] toggle switch (16g), then to the + side of the light string, thru the string, back to a negatvie terminal (16g) which grounds to all other accessories.

 

[ajgraz]

Re: Fuse Rating Selection

I'm thinking the LED's in the rope are parallel, kind of like a string of xmas tree lights. I'd hope so, so if one goes out they don't all go out.

It'd be frying the wire I'd be most concerned about.

What you're planning sound Kosher to me. How much length are you adding with the 16awg wire? 16AWG might be overkill.

 

[bds85466]

Re: Fuse Rating Selection

It's all spec at this point, but the back of the the fuse and the switch should be in reasonably close proximity...several inches max. I was just thinking an in line fuse holder of some sort (not sure which gauge those fuse holder leads would be). I'm not sure yet what g wire the LED leads are...they're in the mail!

I'm guessing the switch will be rated for what, like 20 amps assuming it's a decent one?