LEDs. Help!

[Guest]

Hey there.

This is my first time messing around with LEDs, but saw an article by Bareass choppers and they made it seem very straight forward. So, I switched things up off the jump and went ahead and bit off more than I can chew haha.

I need help calculating what resistor I need on the tail light power. All the calculators online are for single bulbs, I have built two arrays of four leds and need them to function with dim (running) and bright (brake) functions. Most of the info I needed was taken right from what was in the Bareass article. However, with fewer leds in my cluster than theirs does the resistor on the running light power need to be changed to make up for the difference or am i over thinking things?

Im thinking that it might still work but wont dim them to the same extent that it would have with 12 leds making the difference between my running and brake lights less noticeable. I just want to make sure its obvious enough for the space cadets out there, they scare me enough as is. A blonde air head stopped opposite me at an intersection waved back when I made a right yesterday…

Ill include a link to the original article and a crude little diagram of what I have so far pointing out which resistor it is I am unsure of. 12v system by the way.

Side question, how are all the nice diagrams i see on here created? Mine is embarrassing and Id like to do a better job next time haha.

Heres the original article

http://tech.bareasschoppers.com/diy-projects-mods/rear-lights-mod/

[Guest]

Forty some odd views and no replies? I know theres got to be some electro-tech mad scientists on here! Haha.

Went by Radioshack and the guy just walked me over and opened up a bunch of little bins. I stopped him as he walked away and explained what I needed help with. He told me he didnt know what resistors actually were, he just knows where they are.

Asked the same question on a LED site and they told me just to build to lights, one for each function…

Im at the mercy of the CULT!

[seaking]

Man I took electricians classes for two years in high school and I can't remember enough to understand that article. First, both circuits are sharting the same common feed line. So wouldn't both circuits light up at the same time? Second, IIRC each resistor's capacity should be half or 1/3 whatever of the main line. So if I have a 30A circuit, 15A can feed two circuits (15Ax2=30A). I guess I don't know wtf I'm talking about, and I don't really think it matters. I'd just buy a 220 like he did and call it good.

[Guest]

There are two power feeds. one for tail, with the power knocked down to dim them a bit, and a brake power that only feeds when the switch is triggered (not in the diagram) so when it IS triggered the leds receive more power and get brighter.

But thanks for the response, I think I will just go ahead and wire it up the same way. If it fries it Ill only be out a dollar or so. At least theyre cheap.

Ill post up picks whether it works or blows up!

[jimg]

http://led.linear1.org/led.wiz

You have a parallel array. I don't understand the one resistor. I may be a 1/4 W same as the others

[Guest]

http://led.linear1.org/led.wiz

You have a parallel array. I don't understand the one resistor. I may be a 1/4 W same as the others

Not sure how to use that to my advantage. I know the 270 ohm 1/4 watts are correct and in the right place, adding another to make it run dim confuses me though. I know the 220 will dim it, Im just not sure about the amount it will dim it since I have four less LEDs than the original article, and would like the brightness of the two functions obvious.

Thanks for the reply, Im just clueless and the stuff ive read trying to figure it out hasnt helped me. Its unclear to me how the resistors build upon each other/work together. New to all this and hard to wrap my head around. Ill post how things go as soon as the diodes show up in the mail.

Thanks again guys

[TheLawWon]

It's been awhile since I've done any work with electronics, but here is one possible solution to your problem. Use a potentiometer, basically a variable resistor-- read adjustable-- in place of the 220 ohm resistor in your wiring diagram.

Experiment with it to find the amount of resistance to achieve the desired level of brightness. Then measure the resistance with a multimeter, get an appropriate resistor, solder it in and you should be good.

You can probably find a "pot" as they are called at Radio Shack or any number of vendors on line.

By the way, the 270 ohm resistor is the current limiting resistor. That will limit the current the LED can draw so it cannot blow itself up.

Let us know how it works. Looks like a fun project.

[Hotlumpy]

The more resistance the resistor has the more of the energy it will use and the dimmer the light will You need to take into account the resistance of the led array, if you use a resistor equal in resistance to the array of ledsit will halve the voltage between them. If you use a resistor with 1\3 of the resistance of the led array the bulbs will get 2\3 of the voltage,yadda,yadda. If the diagram you were building from used 12 LEDs and you are using 4 of the same resistors(1\3 the amount), then I think I would start off with a resistor 1\3 of the value they suggested, or vary the value accordingly if I am misunderstanding how many LEDs you are using in comparison to the original plan. I would just use the same wattage units they suggest. You are basically just using the resistor to split down the voltage to the bulbs in the running lights mode , and the diodes are there to keep the run/stop circuits from back feeding each other and acting as one way gates. That help?

[Hotlumpy]

And honestly I think the other resistors are there because they are using the more commonly available 5 volt LEDs and needing to drop the voltage from 12 volts. You can buy 12 volt LEDs at radio shack. Honestly calculating a resistance value about equal to your array and putting a potentiometer that works in that range might be a good idea to get it just how you like it

[dirtbag]

Dude its not like everybody that reads this shit even posts,or knows.Wtf are you saying theres nothing online I just did this and found a online caculator, i plugged in the size and array of led's as I ran 2 different circuits one for running lights and one circuit for stop lights with 2 different resistor sizes I was able to find locally at a electronics store, radio shack didnt have shit that would work http://led.linear1.org/led.wiz I think this is what I used. You will need the specifics for your l.e.d.I ordered the l.e.d.'s from china for $1.99 with free shipping.

[jimg]

Looked some more on the web:

http://electronicsclub.info/leds.htm#calculate

http://www.sengpielaudio.com/calculator-paralresist.htm

[Grantman]

Going by what I remember I would ballpark it at about a 130-150 ohm resistor. Don't read so much it'll make your brain hurt. A lot of this shit is theory that you need to understand, not calculate. LED's and all the other bits and pieces are so cheap, I wouldn't sweat it too much. Put the crap together and test it in the shop on the bike for 30 minutes running light only and do temp checks on your entire system, if it don't heat up it won't burn up. Then repeat the same test for 30 minutes with the brake lights on. 30 Minutes is stressfull enough on the system to let you know if there is a problem. If shit gets hot, get a bigger resistor. A potentiometer is a great way to dial shit in if you are going to get reall picky. Go in steps. More resistance (bigger ohm value) means less current so lights will be dimmer and less heat will develop. Your wiring should be stout enough that the heat will never be an issue anyway. Less resistance (lower ohm value resistor) will allow more current to light shit up brighter. Just remember energy and heat are the same thing. You aren't building a nuclear weapon, it's a lighting circuit.

[Demin]

I didn't read every post,so if I duplicated..I'm sorry.BUT.....

Thank God for The Horse.Nov.'09 Has an article about 1 wire leds.Brewdude Made a taillight from an LED marker light.He said he used a 100 ohm resistor because he wanted a little brighter taillight.He said if you don't want the tail as bright try a 150,180......The higher the number,the dimmer it will be.