Resistor/LED Question

[DBMaster]

What value resistor would I need to use in series with a white LED to replace some indicator lights with LED's. I bought a pair of amber 194 LED replacement lights for my front corner markers and they had resistors in them. I am having trouble decoding them with my handy resistor code reader.

I can't tell if they are 2, 10, or 20 ohms. It would seem like they should be 2 based upon the calculation V=IR, but I don't know what R is for the normal circuit.

I know a few of you have done this. I want to replace my D4 light with an LED so I can quit messing with it. The others are rarely on for more than a few seconds at a time so I am not worried about those.

Thanks!

[Mac]

Can you see the colors of the bands on the resistor? If so post them in order from top to bottom. Top is stripe closest to wire lead.

[Immeraufdemhund]

I dowbt that it will have the colors on it. Big Birly Roy...hehehe

gosh i'm supprised i still remember that one. with LED's i bet it is in parallel with the circuit so that you dont loose any brightness. Well wait..hmmm could be in series i suppose because of the amps running to the bulb might be too high for the car.... might not even be a resistor... dang it too many possibilites for my wandering mind...

[Sabz5150]

Originally posted by Immeraufdemhund
I dowbt that it will have the colors on it. Big Birly Roy...hehehe

gosh i'm supprised i still remember that one. with LED's i bet it is in parallel with the circuit so that you dont loose any brightness. Well wait..hmmm could be in series i suppose because of the amps running to the bulb might be too high for the car.... might not even be a resistor... dang it too many possibilites for my wandering mind...

Bad Boys Rape Our Young Girls, But Violet Gives Willingly? That was one of the 'unofficial' ways we were taught :lol

If it has the bands, here's how to decode them.

There are four bands. They are all one of these colors:

Black = 0
Brown = 1
Red = 2
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Violet = 7
Grey = 8
White = 9

Silver = 10%
Gold = 5%
Red = 2%

Say you have a resistor with the color bands: Red, Blue, Orange, Gold. The first two numbers are the first two in the value. Red is 2 and blue is 6. This makes 26. The third number tells how many zeros to add to the end of that. Orange is 3, so your resistor's value is 26,000 or 26K ohms. The fourth band is the tolerance. Gold is 5% tolerance. So your final value is 26K ohms plus or minus 5 percent.

Some resistors have a fifth band, denoting *fault* tolerance, however these are usually reserved for military/research use.

Hope this helps

[johnwc723]

ehh i think it needs to be parallell, well thas how i did it my overhead lights in my car are a circuit board made by me with 6 leds in it

by the way they are blue and raw as hell, but highly illegal i think ...

[TWOLOUDNPROUD]

720 ohms to make a 3V Led to a 12v Led

[DBMaster]

Actually, I got this formula. The voltage is not that important as an LED will light with anything at or beyond its "forward voltage." The resistor is used in series on either the + or - side (LED's are directional) to cut the current to stop them from burning out.

(Vs-Vf)/If = R

Vs - System voltage, use 13.8 for automotive applications
Vf - Forward voltage of LED - from the LED specs
If - LED current - from LED specs (don't forget to multiply by 1,000 as this value will be in milliamps)
R - resistor value. You should always go a good bit higher.

I calculated a 680 ohm value needed for a super bright white LED I bought to replace the burned out bulb in my D4 indicator. After talking with the owner of the elctronics place I went with a 1.2K ohm resistor as he said these LED's were "really bright." I got it all done and now D4 lights about twice as bright as all the other gears, almost to the point of distraction at night. But, I accomplished what I set out to do.

Since there is a lot of disassembly involved in replacing a bulb in the cluster shift indicator I don't want to do this again!