Footwell light mod questions

[Taliano]

Hello,

I need to ask a few questions about DIY footwell lights in a car. I plan to wire some in soon.

Here's the background first:
Many of the people on the car forum I'm a member of are tapping the wires of another already-existing light in the car. The already existing light illuminates a storage hole. So people are connecting the red LED wire to the red car wire, and the black LED wire to the black car wire.

Here is a diagram of what they are doing:

(the wires labeled as 'cubby wires' are the wires that supply the storage hole light)


And here is the LED I plan to use from superbrightLEDs.com:

These are the specs on this bulb:
LW-x-12VDC Wired LED
LED with 3 foot long 30ga. stranded wired
Built-in resistor for 12 Volt DC operation (9~14.8 Volt range)
30 degree Viewing Angle LEDs, Black Nylon panel mounting bezel included

Now, consider,
1) I wire one on each side, so a total of 2 red wires are being tapped to the car's red wire, and the same with the black wires.
2) I tape the exposed copper up and ensure the red and black don't cross current.
3) My car is a 2006 Acura TSX if that is important.

I just wanted to inquire about the safety of this method of tapping a wire. People have done it on my car forum, but I am gathering as much info as possible before doing this to avoid electrical damage. Also, if there are problems that can arise, what are they, and what are alternative ways to wire my footwell lights?

Some people on the car forum were saying that a safety precaution is to run an inline fuse, but I don't know what that means, or how to implement it in wiring. So any info/advice on this would be a great help.

Thanks

 

[LEDobsession]

Put the fuse just before the tapping point on the positive (red) or just before the resistor to the LED also on the positive wire. Either way will work. If you have the fuse before the tapping point, you will be protecting both the LED and the Cubby light. If you put the fuse before the LED only, it will only protect the LED.

 

[shortstack]

to be honest you dont need to add a fuse, the car already has one for it, plus the led uses such less power it wont make a difference

 

[bretti_kivi]

the car probably won't already have "one for it". It will have a fuse on the supply side of the black box which controls the interior lights, NOT on the rear of it.
At least, I don't see how that would work. You have one fuse for all "dome lights", right?

Check the power rating of the original lights. If you're only adding a couple of 5mm LEDs with 680Ohm resistors (don't forget those!) then there shouldn't be an issue.

Bret

 

[Taliano]

So, the added fuse will only protect the cubby and LED lights? The fuse won't protect me from damaging the electrical in my car i.e. shorting out all my lights, will it?

Some people on the Acura forum had ALL their lights short out, and it was expensive damage. I just want to make sure the lack of this fuse you talk of won't cause THAT.

So more clearly stated, if I don't add the inline fuse and just tap like my diagram, will that increase the chances of expensive electrical damage (beyond just burning out the bulbs themselves)?

Furthermore, the LED is 12Volt DC. I'm pretty sure that was meant for cars. Also, people have done it with the same LEDs in the same car, so I guess this LED I am going to use is safe.

ALSO, do you think it would be safe to wire FOUR LEDs all to the same cubby light? How many do you think I can wire before overdrawing or otherwise overloading the electrical system? I would like to wire up to 4, but I'm going to try 2 at first.

Thank you guys for all your advice. It is very valuable and helpful.

 

[Norm]

You won't need to fuse the LED but I recommend you use the correct size Scotch Lock connectors, you should be able to buy them from any auto accessory store.
YouTube - Scotch Lock Wiring Connector - etrailer.com
Norm

 

[bretti_kivi]

I am no fan of "12VDC LEDs". I'd personally prefer to get a known good LED, like a Nichia 44000mcd - and then run that with a 470 or 680ohm resistor.

Shorting out all your lights... well...

let's go back to the start. I don't know what's on the same electrical system. Check it; I have over-sunvisor lights (@5W each) on the same circuit as my interior lights. So, adding another 10W of LEDs isn't going to cause any harm. IF there's only one light on the circuit, then I'd be wary about adding much more than 100mA to it. Check it, work out what's connected, do the math and work on the cautious side.

Bret

 

[Taliano]

^^What is 100mA?

I need a concept of what 100mA means so I can compare my LEDs with that value. How many mA units would a typical 12VDC LED use?


Thanks again for you guys' help.

 

[irsa76]

Many years ago I added a pair of 5w incan globes to the foot wells of my car by simply tapping directly into the OE dome light harness. No fuses were added. I simply copied the factory set up, with exception of the small fact I spliced direct onto the dome light rather then use a plug like OE.

 

[bobski]

^^What is 100mA?

mA stands for milliamp.
Milli is a prefix used by the SI system of measurement units that means 1/1000th. Millisecond = 1/1000th of a second, milliliter = 1/1000th of a liter and so on.
Amp = a measure of electrical current - the number of electrons flowing past some measurement point in a given period of time.
So 100 mA means 100 1/1000ths of an amp, or 0.1 amps.

Measurements to be familiar with:

Voltage. A measurement of 'electromotive force'. You can think of it as the electrical equivalent of pressure in a water pipe.

As I already said, current, measured in amps. In the water-in-a-pipe analogy, you would be measuring how fast the water is flowing through the pipe.

Watts... a measure of work. Volts * amps = watts.

Resistance, measured in ohms (generally written as the greek character omega, which looks like a horse-shoe). Resistance is a measure of how much a given component restricts the flow of current.

I need a concept of what 100mA means so I can compare my LEDs with that value. How many mA units would a typical 12VDC LED use?

5mm LEDs generally max out around 20 mA, so you could wire up 5 of them in parallel (all of the positive wires together, and all of the negatives together) to reach that 100 mA mark. But then, that's being cautious. They may only be drawing 10 mA a piece... it really depends on the value of the resistor under that shrink-wrap.

 

[Taliano]

I just got the LEDs in the mail yesterday.

The 5mm LEDs I have use 20mA I believe. One guy on my car forum had 6 of these wired to the same cubby wire, so I'm starting to realize 3-4 will be okay.

I replaced the filament cubby light itself with an LED too, so will this replacement itself reduce the current draw?

The caution I took by asking on here was well worth it, and your advice was helpful and valuable.

Thanks for your time.

Anymore advice anyone might want to add will be just as valuable and useful.

Again, thanks.