little help with putting LEDs in car!

[CodyjCA]

Im going to set up a system in my car where i press a switch and a lot of LEDs turn on in my car, in various spots, im looking at around 10 or so LEDs (in vents, under seat, pointing at pedals etc etc) its best not to ask why but i just need help wiring.

Since these blue LEDs are around 3.5 V and im going to have around 10, so thats 35 V, will that dim my lights or make my battery run out fast? any problems with that?


if anyone can help me out wireing that would be awesome.

i wanna hook it up in a serese with 1 resister so they all get the same voltage. thanks for your help!
!!!

[Silver Streak]

Try searching google for some information on LEDs...it sounds like you know the terminology, but nothing you wrote makes any sense. Not trying to be rude.

It's the amp load that'll kill your battery, not volts. 10 LEDs is nothing, if they're about 20ma, you can probably run like 2000 LEDs safely! You have absolutely nothing to worry about.

However, it doesn't make any sense what you're trying to do. A car battery is 12 volts. 10 LEDs x 3.5 V = 35 Volts. Why do you need a resistor, heck they probably won't even light up if they're in series. Who told ya you need a resistor?

You can run 3-4 of them in series, and you'd be fine. However, since you're sticking them all over the place, you'll need one resistor PER LED...without know all the specs of your LED's, try using a 660ohm resistor to play it safe.

[JetspeedCamry]

Why not just have a resistor soldered to each LED of about 300ohms (if the LED's you are using are 3.5V, they would be Blue, UV or White hi brightness LEDS). Then just run 2 wires to each one (use some small speaker wire) from a junction box that will house the main powersupply entry and switch etc.
Because they would be in a parralell config, the voltage to each LED would be 12-14.4V (dropped with the 300ohm resistor). If using 10 of them..u'd draw 200mA from your main supply, which is nothing for a car. You wouldnt notice any dimming. I wouldnt recommend leaving them on all night though!

[CodyjCA]

Holy dump you guys are so fast!
so i dont know much about electronics so thanks for clearning up the mA and volt problem,
silver streak, this is what im trying to do

http://www.theledlight.com/img-tech/parallel101.jpg

so i should run 2 wired to each led? with that picture they used 1 resistor, but i dont have a problem with putting a resistor for each led

another noob question, how should i split the power cord 10 ways?

also what kind of requirements should my switch have?
thanks jetspeed, uve been helping a lot

oh yea, my leds are blue, 3.5 v 6000mcd

[JetspeedCamry]

In that diagram..having one resistor is fine..for voltage control..however..the power rating of the resistor has to be increased, as all of the power for the 3 resistors is going thru it. Thus is gets bigger.

Power = Voltage x Current

P = 12V x (20mA x 10)
P = 12V x .2A
P = 2.4W

So..with that setup you'd need a 300 ohm, 2.4W resistor..which is quite big, compared to having small resistors. Depends, either one may be the cheaper option..chech your electronics store.

And yes..youd run 2 wires to each LED. Even if you used that diagram..you'd connect the positive ends of the wires to the resistor, instead of the supply.

The connect ten wires, each could be simply soldered together at the end, wrapped around the lead of the resistor. Or perhaps a terminal block of some sort.

Keep in mind, that if you use a single resistor, 2.4W rated..you will also have more current running thru your wires. Having indiviudal resistors means you can run thinner light duty speaker cable to each LED, meaning easier routing etc.

[88 LE]

^ Not quite.

3.5V across the led @ 20mA:


12V - 3.5V = 8.5V / .020 = 425 ohms

13V - 3.5V = 9.5V / .020 = 475 ohms

14V - 3.5V = 10.5V / .020 = 525 ohms


I think you meant to say 2.4 watts not 2.4 amps. 2.4 amps @ 12V = 28.8 watts.

[JetspeedCamry]

Originally Posted by 88 LE

^ Not quite.

3.5V across the led @ 20mA:


12V - 3.5V = 8.5V / .020 = 425 ohms

13V - 3.5V = 9.5V / .020 = 475 ohms

14V - 3.5V = 10.5V / .020 = 525 ohms


I think you meant to say 2.4 watts not 2.4 amps. 2.4 amps @ 12V = 28.8 watts.

Sorry...yes..2.4W.

[CodyjCA]

is a fuse essential for this project?

[JetspeedCamry]

A fuse would be a good idea. Have it inline on the main positive lead. It will prevent melted wires or a stuffed battery (fire hazard) if two wires happen to touch..
If each LED draws approx. 20mA and you run 10 of them..the total current draw of the system will be 200mA. Get a fuse rate for 50% more than that. Say..300mA. If there ever was a short..this rating would cover it nicely, without there being problems with small current fluctuations. Another way is to connect up the whole system, and use and ammeter in series on the main positive wire. Read the current draw and then install a fuse to around that (more not less).

[fox_prime]

it's very important to note the terminals of a LED. the longer strip is positive and the shorter one is negative. if you reverse these during your connections, you may short (or blow) a fuse or even the LED itself.

[JetspeedCamry]

Originally Posted by fox_prime

it's very important to note the terminals of a LED. the longer strip is positive and the shorter one is negative. if you reverse these during your connections, you may short (or blow) a fuse or even the LED itself.

Correct and not correct.
Yes, you need to be aware of the correct terminals on the LED for it to work, ie. Longer one is positive and shorter one negative, however, a LED stands for "Light Emitting Diode". This means that if you get the connections wrong, ie. reversed polarity on the LED, it simply wont light up. That is all. It wont do any damage to anything, not even the LED, as when reversed, it acts like a normal Diode. Diodes only allow current to flow one way. In the case of an LED, it's exactly the same, just that it lights up at a certain wavelength, as a normal diode doesn't.

[McTimson]

What will damage it though is too much voltage, so make sure you get the proper resistance before you install it. Also, be careful when installing them, don't let either lead touch the other while they are connected to a power source, as that will burn the LED out instantly...

[CodyjCA]

yea, i had some experience with buring out 3 ledsin a finished project (really pissed me off)
i bought 4 leds from lsdiodes.com for like under $5 and i messed 3 of the LEDS up so i bought 100 off ebay, with 100 resistors (and they are brighter also) for $17, so if anyone wants any blue 3.5v 25ma 5900mcd leds then im the man to talk to

[McTimson]

Did you get them from that guy in China, or Japan, or something? I've bought tons of LED's from that guy, they're great!