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What size fuse to use?

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melanie

Joined: May 12 2010
Posts: 4


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Post Wed May 12, 2010 3:47 pm

Hi,

I have recently installed two 9.5 LED strips (one per footwell) and will be adding 10 of the pre-wired surface mounted LEDs, as well as four 4.7 inch flexible LED lightstrips.

I am going to run the wiring for all of this through an "add-a-fuse" attached to my fusebox.

Is 5 amps sufficient for my project?

Thanks!
PwrRngr

Joined: Jul 19 2007
Posts: 4407


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Post Wed May 12, 2010 6:34 pm

It depends on what size wire you run. The proper way is to fuse for the wire size, not the load on the circuit. Please see this thread:
https://www.oznium.com/forum/topic15761
melanie

Joined: May 12 2010
Posts: 4


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Post Thu May 13, 2010 9:59 am

That is a VERY helpful tabe, but unfortunately, I am stil a bit confused.

The Oznium site des not say what size wire is attached to the surface-mount LED lights - i know that i used the 20/22 hole on the wire stripper the strip them, but I still don't know what exact size the wire is.

The Oznium site "Technical info" for the surface mounted LEDs atate that the current pulled by the orange lights is 60 mA - yet your table states 20 mA. Is the 60 mA including the wire?
What about the 18 gauge running wire I used?
PwrRngr

Joined: Jul 19 2007
Posts: 4407


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Post Thu May 13, 2010 11:03 am

If you used the 20 gauge hole, then fuse the entire circuit for 20 gauge wire. You always fuse according to the smallest wire used (largest number = smallest wire). In this case, it sounds like it's 20 gauges.
melanie

Joined: May 12 2010
Posts: 4


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Post Thu May 13, 2010 8:30 pm

So, let's see if I understand this correctly...

What I currently have is:

(6) surface-mount LEDs @ 80 mA= 480 mA
(2) 9.5 inch flexible LED strips @ 160 mA= 320 mA

for a total of 800 mA, or 0.800 amps

In any case, the 20 gauge wire looks fine, an 5 amps looks like perfectly adequate coverage to me...


I wanted to add (4) 4.7 inch LED strips, as well as 4 more surface mounted LED - which would add:

4 x 80 mA (320) plus 4 x 60 mA (240) = 560 mA for a new total 1360 mA or 1.360 amps.

Looks like the 20 gauge wire and 5 amp fuse is still OK...

That is a wonderful chart and explanation - thank you very much!
Tat2Dragons

Joined: Jan 21 2007
Posts: 3404
Location: Baltimore Maryland


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Post Fri May 14, 2010 12:09 am

^^If you look around a bit you can actually find 2 amp ATM/mini fuses. icon_smile.gif I've bought them in the past at the local Pep Boys.
Moss

Joined: Mar 23 2004
Posts: 6436


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Post Fri May 14, 2010 12:07 pm

Tat2Dragons wrote:
^^If you look around a bit you can actually find 2 amp ATM/mini fuses. icon_smile.gif I've bought them in the past at the local Pep Boys.


Radioshack as well.
melanie

Joined: May 12 2010
Posts: 4


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Post Fri May 14, 2010 7:52 pm

This begs the question....is there any advantage to using a 2 amp fuse instead of a 5 amp fuse?

Conversely, is there harm in using a 5 amp fuse where a 2 amp would be sufficient?
Tdawgthegreatest

Joined: Jul 22 2007
Posts: 5093
Location: Florence, Oregon


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Post Fri May 14, 2010 11:50 pm

if anything less than 2 amps is required to go through to your lights, a 2amp is nice.
If 3 amps tries going through your fuse, it pops.

If your lights NEED 2amps or less...and your using a 5amp fuse. And anything more than 2amps goes through it, could damage your lights.
Moss

Joined: Mar 23 2004
Posts: 6436


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Post Sun May 16, 2010 1:41 am

Use a 100 amp fuse.
PwrRngr

Joined: Jul 19 2007
Posts: 4407


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Post Sun May 16, 2010 4:11 pm

melanie wrote:
This begs the question....is there any advantage to using a 2 amp fuse instead of a 5 amp fuse?

Conversely, is there harm in using a 5 amp fuse where a 2 amp would be sufficient?

Seriously, don't listen to Tdawg b/c he obviously doesn't know what he's talking about (no offense, but it's obvious from your statement). If your lights pull 2 amps, they will NEVER draw more than that unless there is a short and then they will draw more than enough current to melt the wires. On to your question.

No, there is no advantage of using a 2A fuse instead of a 5A fuse. A 2A fuse is NOT any safer than a 5A fuse.

But, there are MANY disadvantages. If you expand your lighting later, you'll have to replace that 2A fuse. If you continue expand and change your fuse, there's a good chance you'll exceed the current capacity of the wiring. This will fry the wiring and there's a good chance it could catch your car on fire. This is why you ALWAYS fuse to the wire size and NOT the load. If you ever have to change the fuse b/c it keeps blowing, you know you also need to upgrade your wiring.

Second question, there is no harm in using a 5A fuse where a 2A would "work" (assuming the wiring is sufficient for a 5A fuse). The correct way is to use the largest fuse possible for the wiring. Hence the purpose of the thread I linked you to.
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