Ok guys, whip out your Physics books,

I just ordered some LED's off Ebay and would like to wire them into the foot wells in groups of three to light them up when the doors are open, later on I will move to the Dash and switches etc. But for now I just have simple wiring Questions to throw at ya.

Here are the specs:
10mm Red LED's
2.2v
30mA

If I wire them into groups of three should i wire them in parallel with one resistor, or series with one resistor. Or should I put individual resistors on each of them. AND what rating (ohm's) should the resistors be??

 

I would use a resistor for each LED. (Resistors are cheap).
To calculate the resistor:
Voltage accross the resistor: 12V - 2.2V=9.8V
Voltage=Current * Resitance therefore the resistance equals the Voltage divided by the Current: 9.8/.03=326 Ohms. The closest value will be 330 Ohms.
The wattage for the resistor has to be at least 9.8V * .03A = 0.294 Watts. I would use 1/2 watt resistors.

Anyway a 330 Ohm, 1/2 watt resistor per diode will do the trick.

Arjan

 

Series wired, one resistor.

Leds should be driven at 20mA, not 30mA, unless you want them to die early.

V=IR

Normal car battery voltage is about 13.8, so:

(13.8 - 2.2 -2.2 -2.2 ) / .02 = 360 ohms

Power = I^2 * R, so the minimum power rating of the resistor should be:

.02*.02 *360 = 0.144 watts.

 

thanks guys, quick response.

I think i will run them at 30 because they were advertised as ultrabright, long lasting, which i think means that they can withstand a little more current. but I'll see when they burn out right:pat:

 

In my calculation I took the resistor value above the calculated value. If you take 13.8 volts at 330 Ohms you'll run at 41mA. So you might want to go one step up to 390 Ohms. I don't think there is any values in between those numbers unless you get into higher end resistors. Normal resistors are manufactured at 10% accuracy so a 330ohm could be as high as 363Ohms and a 390Ohm could be as low as 351Ohms. That's what they told me at school anyway. For that reason they don't make the values in between unless you take 5% resistors and I think they have an extra colour band.

I would try running a LED with the 330 Ohm resistor for awhile and if it last do the rest. You could also use a 12V voltage regulator to pin the voltage at 12V. A bit more complicated.

Arjan

 

Get a potentiometer that can handle 1 amp DC 12 volts 1,000 ohms.


Grab a multi meter
Add power,
Twist pot knob until you see 2.2 volts
Remove pot from power
Take meter and test resistance from one end to the other

You got your resistor value.



Math is good but, pratical works too.

 

You could save yourself a little trouble and use regular lights like I did....



One of my favorite mods!

 

LEDs sounds like a pretty neat idea since they are very energy efficient and produce no heat.
Wouldn't take many to produce alot of light down there.

Make sure you do a writeup when you finish it.

 

He's right, I have been working on this exact same project, but I went with 4 green LED's to being with. It don't produce enought light. I then went with the expensive SUPER BRIGHT green LEDs, that were 2.85 a pop. These are much better, but only ordered one so far. I'm willing to bet you won't see anything impressive if you don't go with those.

Erich

 

I am working on LED footwell lights right now. Got the LEDs from Target in the ricer section of the automotive dept. The name on the box is Hikari dash mood light set-cost $10. It has 2 LEDS on 4ft cords with a cigarette plug. Took the plug off and am hard wiring it to the door lights. Each cord has its own resistor built in. The LEDs are mounted on a swivel base with sticky tape. They are very bright.

 

I used to work with LEDs alot so here are a few pointers:

1) get at least 100 candelas per LED (cheapos and SMTs are in millicandelas) or more
2) power is not an issue but make sure you can supply enuf voltage for driving
3) certain colors are tougher to make that others and are therefore less efficient (ie dimmer)
Brighter - white, yellow-green, yellow, green, orange
Dimmer - Pure red, purple and especially deep blue (because of high wavelength of the light)

For reference:
cell phone backlight -> 5-10 candelas
B/W PDA backlight -> 20 candelas
color PDA backlight -> 50-70 candelas
Notebook display -> 300-500 candelas
Computer monitor -> 1000-3000 candelas


Read more about lighting here:
http://ww2.green-trust.org:8383/lighting.htm


Check out this seriously bright LED (cheap @ $15 for 660 candela!)
http://www.bit-tech.net/review/82/

....or check out these!
http://eng.luxeon.hu/luxeonIII.html

 

Any pics!

 

Sorry, no pics yet. I'm still in the middle of wiring to the door lights. It has been pouring rain for the last 2 days so I can't leave the doors open and everthing apart. Maybe I can finish Sat morning.

 

Sweet mod!