LED light questions - automotive

[KurumaOtaku]

Hi all. I've been seeing a lot of DIY led lights and I've done a search on Google for
some how-to help, but no one really explains the part about resistors/amps/volts.
I don't much about electronics so I don't know how to calculate the correct amount
needed to prevent the LEDs from burning out. Any one can teach me or lead me to a
good website?

[Act162this]

not sure what the particular application you are looking for is, but if you're simply looking to replace taillights, interior lights, etc... it might be easier to purchase a set of led lights with the proper bases than to juryrig something.

the only thing for taillight/blinker combos is the lower resistance of the led lights will cause them to behave strangely (i think they will blink faster) so some lights require the addition of a resistor inline so the flasher module doesn't get confused.

if you're looking for something totally fabbed, perhaps some of the more EE minded types here can help you out. i totally forgot everything i learned about voltage, resistance, etc... in college.

[ikeyballz]

e=IR, P=IE. thats basically all you gotta know...but what makes things hard is that LED's are variable resistance...they change depending on the current going through the suckers.

if things are in series ----[ ]------[ ]----+ the CURRENT remains the same throughout (I) but the VOLTAGE drops between the things - easy way to see this is to hook up two 12V light bulbs like this, hook it up to a car battery..and the light will be DIM.

now, parallel - this is the opposite. voltage remains the same, but current will be split!


.........................../---[ ]-------\
(-) --------------{.....................}------------ (+)
...........................\--[ ]--------/

-if you hook lights up that way, the lights will BOTH be bright.

so..basically, most LED's are LESS than 12V rated. their current/power ratings will all be diff..

so you have to tap a resistor (idk which one, depends on the LED, actually...)

------[resistor]-----((LED))------ 12v+

so that the LED does not BURN out.

the faster blinking is cuz the LED's draw less current than a conventional light.
my bad if you knew all this already...and im not helping..lol

the best thing to do, IMHO..if you wanna do this yourself is:

get a Potentiometer - its basically a resistor that you can vary- the stuff in your (older) radio knobs...? they go from 0 ohms to whatever ohms you want, get a generic one...and go from 0-whatever brightness you want it, leave it at that for a while..and if the LED doesnt burn out in a few days..you should be ok...just drop the resistance a bit MORE when you get a real resistor (factor of safety) -its the dumb, DIY, guess/check method!FTMFW! :D



if someone else knows more correct me if im wrong...alan? hes a EE, im just a mechie. :p




so...i suggest:


-----(potentiometer)----LED----12v+

then after you figure out what you want,

----[resistor]-----(LED)----12v+

[Kreggae]

HIDplanet.com has an LED section. Lots of info on retrofits.

[Zhanshi]

Ike pretty much got it there. For the "ricer flash" I would wire a small resistor inline, ~1 to 3 ohms or so depending on what you can get (wattage matters too). Some potentiometers have an internal resistance so it might not be exactly 0 -> X ohms.

What are you planning on wiring the LEDs to? Most LEDs (not super bright ones) have a max of ~1.5 - 1.8 volts. Your car battery outputs ~14 volts while running. So you would then need to find out how much current your car is outputting (direct from the battery or some wire you're splicing into).

Voltage = Current x Resistance

1.5 volts = Battery Current x Resistance

1.5 volts / Battery Current = Resistance needed

Something like that, summer has gotten me really lazy aha. In any case, those 12v leds that you see already have a resistor connected to them inline (series) or have higher power leds that will evenly distribute the ~12v to all of the leds.

[KurumaOtaku]

Thanks all! That site is really good, but looks like it's a little way over my head.
I'll keep studying. But for now, looks like stock lights will have to do. :|