Ok so I purchased a bunch of LED's to redo my interior and they came with resistors supposedly set up for a 12V system.

Now my problem is that They burned out as soon as they were powered by my car, yes it's 12V. I even tested them out, LED and resistor soldered together, on a 9V battery and they burn out on that also.

Basically I'm frustrated and need some help. I'm thinking they sent me the wrong resistors.

This is what the LED's are rated at, well so they say.

Foward Voltage : 3.2-3.6
Foward Current : 20 Ma

as far as I can tell you need to get the voltage to drop down to 3.2-3.6 Volts. To do this you need a resistor, which resistor though, I have no idea.

There is a place in Needham called "You Do It Electronics" they would probably be able to help you out.

Yea I know I need a resistor. Just need to figure out why the ones I have SUCK. lol and which ones I need since basically every light on this car is a halogen instead of an LED

Im no electrican but do resisitors only work in one direction when soldered onto a board or can they work both ways?

What I've read is they work both directions as long as it's on the postive side of the LED. Which I know it is.

resistors works both directions, LEDs only work one way. If they are reversed, the LEDS can and most likely will burn out. What are the color stripes on the resistor? That will help determine it's resistance value. Also, it technically should not matter which side of the LED the resistor is on. My guess is the resistors should be about 450-500 ohms each.

http://samengstrom.com/nxl/3660/4_band_res...de_page.en.html

also, how are you hooking them up? in series, right? also, if you have a volt/ohm meter (multimeter), you can verify the resistance yourself.

they're Green, Purple, Black, Black, Brown

So according to that link it's 570 ohms.

I don't have them fancy tools haha


Basically what I'm doing right now is replacing the bulbs in the Climate control, Hazard, Defroster. All of that stuff. Window switches IIRC are already LED's so I don't have to bother with resistors.

that should be fine. the higher the resistance, the lesser the chance of it blowing. More resistance = level current, less voltage

hmm but they're still blowing

I'm going to try the window switches tomorrow see what happens with that.

Just for shits and giggles, try the other side of the LED?

How do you work on cars and not have a multimeter?

Never needed one

a diode only allows voltage to travel in one direction if you hook it up backwads nothing should happen try using 2 resistors and see what happens more resistance = less voltage i am not home when i get there i will do the math to tell you what you need exactly but you are prob around 13-14 volts when the car is running the formula if you wanna try it youself is voltage = current x resistance also works resistance = voltage / current or current = voltage / resistance

so use 13 volts as your voltage and 570 as your resistance now find currrent is I=13/570 = 0.0228 = 22mA if it's max current is 20 mA you will need a slightly bigger resistor 13/.02= you need 650 which should is just inside the tolerance


you may have bad info on the resistor cause you should be there with what you got

now my brain itches

still working on my engineering degree gonna hopefully start school again my AS in EET isn't what i truely want going back for a BS in biomedical engineering and Electrical engineering yeah going for both ohms law is the basis of what it is all built on

I understand what diodes and shit do. I'm not running diodes with these.


Well the LED's I bought came with the resistors. So I didn't really pick out the resistors. Yes it's for the max. I think my problem is I was told the car's voltage was 12V and your saying 13V. So it appears I get to go buy some new resistors.

Buy a multimeter!!!!!!!!!! or wait until next wednesday and borrow mine

actually i thik i was wrong it is .02A and i am gonna say 3.3 volts so 13-3.3 = 9.7 volts we need to get rid of so 9.7/.02 = 485 should be all you need so 485 ohms is what you need forget my previous post that would get rid of all voltage which means a 570 ohm resistor should be more than enough resistance we need to know exactly how much voltage in your car where your hooking these up then take that number subtract 3.3 from it when you get that divide it by .02 and that will tell you how much resistance you need.

hope that helps you can get a multimeter cheep at radio shack and should have one they come in real handy just don't try and measure current with it unless you know how to do so if you need any more help gimmie a call you got my number

an LED is a diode it is a light emiting diode but yes the resting voltage of your battery is 12 volts with tolerances up to 15 vols in most cars car audio equipment runs best at 15 volts but thats beside the point most cars when running run between 13 and 15 volts due to the alternator charging it the alternator has to give more than 12 volts to charge it 13-15 depending on how powerful of an alternator you have

Alrighty well this project will probably be put on hold till I can get ahold of a multimeter. I'm going to give the window switches a try tomorrow hopefully they work.

i have a multimeter you can use but i don't think you wanna wait till next week to get it you can get one at autozone or walmart or radioshack prob like $15

this is a nice one from autozone for $30 http://www.autozone.com/selectedZip,02864/...g/selectZip.htm you should also be able to rent it from autozone

radioshack has this one at $20 http://www.radioshack.com/product/index.js...oductId=2103174

sears has a few i like these 2 for the price $7.49 http://www.sears.com/shc/s/p_10153_12605_0...word=multimeter

$19.99 the best i found for the price http://www.sears.com/shc/s/p_10153_12605_03482141000P?mv=rr


you can get a nice one at a nice price and not have to worry about this kind of problem again

Wowza looks like I'm going to sears tomorrow then. The ones I saw at radioshack were 20 and I have a 10 on me haha.

no problem pal

who da man



you da man





as a side note. Yay a tech thread

hahahaha we could have one hell of a tech section on here everyone knows alittle about something but it only comes out when some one needs help everytime someone needs it someone is always there to give a hand i love this place for that and all the bull shitting that goes on it's suck a fun place to chill

I was going to say, I have a meter you can use. Also, the 570 ohm resistor should be plenty right up to 14V. It's been a long itme sinc eI received my degree in Electronics, but I still have a degree in electronics!!!

lol thanks for the help. I'll post up my findings tomorrow.

ed knows his shiznit as well he is the fricken man!

WTF fucking rear window switches are surface mount LED's


I got the front window switches done thou after some cursing but they sexy


Picked up a multimeter just haven't played with it yet. That's my next to do.

I am sorry, i have been scarcely on the computer these days, and i have all the information you need for whatever LED project your doing. I am going to start an LED thread that explains all, and all will be answered in my post.


aim me if you need help right away, and sorry i havent been around fellas!!!

Figured out what i was doing wrong a few hours ago. I'm a noob lol. All is good now.

Im sorry that i didnt check this in time to help you out, I posted a guide for LEDs in this section, so be sure to check it out.

comments suggestions and questions are always welcome!

No problem man. If I used my head and soldered the resistors on correctly in the first place I wouldn't have had this problem haha.