hey guys...

I was hoping someone could help me out in wiring a LED Lightbar. heres what i need to know:

What toes the longer Led wire represent? Positive or Negative?
How do i wire the Leds together? Negative to negative to neg...
What size/type of resistor do i use if i am going to use my 12v Car Battery to power this?
Should i use more then one resistor, if so how is it wired?

I Basically could use a diagram, a badly drawn picture and any other helpful information.

Here are the specifications of the Leds i am using:

100 Blue Leds:

Luminous Intensity -MCD: 2000 Typical / 3000 Max
Reverse Voltage: 5.0v
DC Forward Voltage: 3.3v Typical
DC Forward Current: 20~30 mA
Viewing Angle +/- 10*
Lead Soldering Temp: 260*C for 5 Sec


10 Blue Led's:

Luminous Intensity -MCD: 800 Typical / 1500 Max
Reverse Voltage: 5.0v
DC Forward Voltage: 3.3v Typical
DC Forward Current: 20~30 mA
Viewing Angle +/- 10*
Lead Soldering Temp: 260*C for 5 Sec




Any Information to help me along would be awesome. if you need anymore info. just ask, second any equations you used to solve my delimma could you post that as well?

P.S. i did read the tech article but since i am wiring about 20 of these all up on one bread board i was thinking the information may be different.

 

We will start with the basics of LEDs (because its pretty much all I know).

LED stands for "light emitting diode" (duh). But what is a diode? A diode (I hope im spelling it right) is a resistor that only can flow current in one direction, if you use the conventional electron flow theroy (electrons flow from positive to negtive to generate amperage/accomplish wattage). That means that these diodes will not function if the current flows the wrong direction. All the diodes will have to be connected in series (neg. to pos., neg. to pos. ect.) to have the diodes work.

I have not looked at the article you mention, but I do believe that as long as you calculate the total amperage you will need to flow to light all the lights in series, fuse the circut properly, and you should be fine. Im not sure exactly what you are looking for (flashing, bouncing, or just plain on) but to do most special effects, you need a controller box for it.

Hope this helps,

 

actually electricity flows negative to positive, and to wire the leds wire postive to negative, and to figure out how much resistance you need take the voltage differance and divide it by the amps of the leds. leds are usually 3 volts. and to figure out how big of a resistor ya need wattage wise take voltage times amprage to get the wattage of the resistor, so 9 times the amps of the led. hope this helps so in your case

take 8.7/.30=29ohms (always want to go with the larger number) you can usually tell on the resistor by the color codes on it, if you would like more info on the color codes just ask me for them.

for wattage take 8.7*.30=2.61 (you can usually tell the wattage on a resistor by how wide it is.

and to figure out how to wire them without a resistor just take 12/3.3 but you probably already knew that

I hope this post helps.

 

ok 2 questions... i thought our car batterys give out about 13.47 volts on average?

second is i didnt know i could wire like 4-5 leds without a resistor, are you sure that would work?

 

well i forgot about car voltage chaning when its on sorry, but its like 14.something. and about the leds together you can as long as all the voltage is correct and ya got the right amount together. all a resistor does it lower to voltage acrossed a point hence using a resistor with one led but more togehter it evens out the charge.

 

Conventional electron theroy holds that the electrons flow from positive to negative. This is the theroy that all automotive applications are based off of. Scientists are still unsure of the true direction of flow, which is why there are theroies as to the flow of electrons. There is no right or wrong when it comes to talking about flow, but for most general purposes, we hold the loose idea that current goes from positive to negative.

Like I said, it only matters because diodes can only flow one direction, meaning if you put them in the circut backwards, they will not function correctly. Which way backwards is does not depend on which theroy one uses. The correct end MUST be pointed towards positive, the other towards negaive to have the diode function properly.

As far as the equasions go, yeah you will need to figure out the total wattage that will be used and then determine how much amperage that will take, as in a 12V system, you can only increace the voltage so much.

 

well in my tech class we learned it neg to pos

 

I haven't the slightest clue which way electricity travels (ever hear the lightning argument? that could go on for weeks), but I do know this... I bought two pre-assembled LED bulbs, size 194 for my sidemarkers, and was surprised to see that they did work, but not the same way as a conventional bulb. With the parking lights off, they would blink normally, but opposite the way they were intended (alternating from the front fascia blinker instead of at the same time). When you turn the parking lights on, though, the LEDs didn't turn on, but would blink with the turn signal (not sure if they alternated or not). Do the sidemarkers have two different voltages coming in them depending on the parking lights? I never could figure this out.

 

Ok guys heres what im gonna do... from the information Mirthman said four LED's can be wired without a resistor, but i need like 20+ alltogether. i bought the breadboard yesterday and ill construct this tonight. i just need you guys to check my math for the proper amount of resistors to use. (This is the equation from the Tech Article Rs= (+v - [Vled])/1Led )

13.45 - 5
-------------
20*(.02)

8.45
-------
.4

21.125 ohms

so im going to need some resistors that total 21.1 ohms?

 

yup thats right, voltage differance divided by amprage. but now ya gotta find the right wattage other wise the resistor will burn and those things stink when they do.

anymore questions, just ask

 

How do i find the wattage???

 

voltage times amprage

 

How do i find amperage lol?

PS i bought about 10 1/2 watt 15Ohm resistors, will those be ok?

here is a diagram of something similar of what i want to do, which one is how i wire the Resistors in?

 

The longer lead is the anode, the shorter one the cathode. Without boring you with theory it goes like this. A diode or LED(makes no difference) permits current flow in only one direction. When the diode conducts it provides approx .6 volts drop, meaning there is a difference of .6 volts between the anode and cathode. For an LED to illuminate the cathode has to be closer to ground or lower than the anode. So, the shorter lead you place at ground and the longer lead goes to whatever positive voltage source you have. However, to limit current flow so as not to destroy the diode junction you have to use a resistor to stay around that 20-30ma range. For a 5 volt source 150 ohms is typical for most applications, auto voltage varies up to 15 or so, in that case anywhere from 330-470 ohms should be OK. Put the resistor between the 12 volt feed and the anode. Your drawing as shown, the long lead of each diode goes to the + line, shorter one to the - line. Place a 330-470 ohm resistor in the plus wire-14 LED's @20ma or .02 amps x 14= approx 300ma. 300 ma or .3 amps using 13 volts= approx 4 watts. so, use a 5 watt resistor. I say this because a 5 watt resistor is a common off the shelf unit. Thats why I use the approx resistor values. You can calculate exactly, but most applications can be easily within 10% or so. Remember the resistor will dissapate heat, so mount it properly. Another way to do it to eliminate the need for a resistor is to wire all the LED's in series, however you need to have the right amount of diodes to provide the required voltage drop. 20 LED's in series will drop 12 volts so 20 diodes all in series can be wired in without the use of a resistor. Remember this need not be exact, most components tolerate a 10-20% deviation without a problem..You can use an individual resistor for each diode but it complicates wiring. A common resistor in series with the positive lead makes more sense. Hpoe this was of some help.

 

actually danno i think that much resistence is too much, the two 15ohm resistors i wired up Acc. to my old physics teacher should work fine, i did it like this...

 

If the diodes are all in series 15 ohms is probably OK. Your drawing shows a common positive and negative bus meaning the diodes are all in parallel, perhaps my mistake. However if they are in parallel 15 ohms is too low. Using I=E/R, in a parallel circuit each diode in the circuit would have to dissipate .8 amps or 800 ma. Way too much. I based my opinion on the right side of your drawing, it does not show a connection indicating a series wired circuit. Rule of thumb for most generic LED's using 5 volt source your current limiting resistor should be approx. 150 ohms, using 12 volt source anywhere from 270-390 ohms. These values are approximate but should work well in most applications. Depending on your circuit don't forget to calculate the power dissipation of the resistor.

 

<-----------------------Knows nothing about circuts, fill me in man.

I tested the lightbar today on a 9volt and the resitors got pretty hot, so i am worried if i put the 12volts through it may burn out the resistors..

 

12volts----LED---LED---LED---ground This is in series


..............I--LED--I
12 volts --I--LED--I---ground --- this is in paralell
..............I--LED--I

In series each LED drops a little of the voltage, so they all share the same 12 volts

In paralell they all get a full 12 volts and this draws a lot more current

 

A little better picture to make it easier to understand

 

Ok got it, i knew that much, my question is will the two 15ohm resistors be alright, is them getting very hot with a 9 volt a problem?

 

Hey man, let me help you out. I am an electrical engineer with a TON of experience w/this stuff.

You should have a resistor for EACH LED. This is the proper way to hook up LEDs. Certain LEDs will 'hog' current from the other ones in the setup you have, thus making varying brightnesses and also making it very difficult to calculate the amperage each one draws (note the 20-30ma RANGE).

Wire it up like this:

--BATTERY -------
| |
| R
|--/\/\/----LED---| (10 Resistors)
|--/\/\/----LED---|
|--/\/\/----LED---|
|--/\/\/----LED---|
|--/\/\/----LED---|
|--/\/\/----LED---|
|--/\/\/----LED---|
|--/\/\/----LED---|
|--/\/\/----LED---|
|--/\/\/----LED---|

For the set-up you have you should have I would calculate your resistor values the following way:

R = (Battery Voltage - Typical Forward Voltage) / (DC Forward Current)
Battery Voltage in a car is ~ 13V
Typical Forward Voltage = 3.3V
DC Forward Current = 20-30mA , use 30mA for maximum brightness
So the resistance you need is:
R = (13-3.3)/(0.03) = 323. Use 330ohms - they're much more common.

As far as power, I don't even have to calculate it, you'll be fine with 1/4 watt resistors, but if you wanted to calculate it, then do this:
resistor power (P) = Voltage ACROSS the resistor / the resistance.
The Voltage across the resistor is: BAttery voltage - LED forward Voltage = 13-3.3=9.7
So your power dissipated on EACH resistor is:
P = 9.7 / 330 = 0.029 Watts Use a 1/4 Watt and your good...

Ok, if you still want to do it the way you had before then you should do this:
For the 10 LED light bar:
Total current = 300mA => R = V/I = 9.7/0.3 = 32 ohms.
Power = IV = 0.3 * 9.7 = 2.91 Watts

So in your original setup, you must use a 3W resistor or higher of about 32 ohms in series with the rest of the LEDs:

|------------------------------------------------------------
BATTERY (The L's are LED's) L L L L L L L L L L
|-------------/\/\/\-----------------------------------------
R = ~32 ohms and 3 Watts

But again, I do NOT recommend this; you may have problems like some may get brighter than others or some may even burn out because they 'hog' so much current. You need the resistors for EACH LED to regulate the current going to EACH LED.

BTW - The longer lead on the LED is the positive.
- You can put resistors on the positive OR negative side of the LED
- The way you can tell the resistor wattage and value is by reading the colored stripes on them. The best way to find this out is to do an internet search - I'm sure you'll find a site that explains it.
- This is not an exact science so if you scrounge some resistors that are off by 5ohms or so you'll be fine. Use them.


I hope you aren't confused - let me know if you have any questions.

 

ok you answered my question. im sorry but i wont use a resistore for each LED, i will take my chances on one being dimmer then the other. but i will get some resistors with a higher watage. so i will need 2 15-16ohm resistors at a wattage of like 3-4 each? cool man thanks.

 

HS, technically MD is correct about limiting resistors being recommended for each device but since you were working with your teacher I did not want ot bore you with engineering criteria. As long as you don't mix different types from different vendors you should not have any problem. I have a friend who makes illuminated signs using LED's. He wires them up all in a series circuit and runs them off 110 volts directly. They run for years in most cases. Just try to use all of the same brand and type. One thing I did want to mention, you might want to use a 3 terminal 5volt regulator IC. Check with your teacher, he should be familiar with them. Since a vehicles electrical system does vary sometimes several volts it may be something to consider. They are easy to hook up and cheap. See what he thinks.

 

HS = Me??

Um thats the thing guys, i wanted to take an electrical class for stuff liek this but theres a buncha pre-reqs i would need and i dont want to go out of my way to take a class not affiliated with my Major. In essence you guys are my teachers and im sorta picking this up as i can understand it.

 

WHAT ??? Scientists aren't sure yet ? What kind of crack are you smoking my friend ? If you don't know, let other people teach you. Electrons flow towards the positive side of a circuit. This is the basic principle that old tubes are based on! Take this from an electronics engineer

 

I know I'm kinda' late here... But here was my thread over on ClubGP with a related diagram...

http://www.clubgp.com/newforum/tm.as...ode=&s=#694143

 

the highest wattage resistor i can find is a 1 wat resistor unless i use those ugly bar looking resistors. is there anyway to achieve about 3 watts of resistence in addition to the two 15ohm 1/2 w resistors im using?

 

After reading that link that backinblack posted i see things a bit easier but i have a question...

his equation was:

LED Drive Current(mA) * Supply Voltage = Resistor wattage.

my question is what if ther eis multiple LEDs is the equation constant or does it change to:

n(Led Drive Current(mA) * Supply Voltage = Resistor wattage

where n = the number of Leds.

 

6 100 ohm resistors in parallel will give you roughly 16 ohms at 3 watts power. Unfortunately when you get over a watt you are dealing generally with wirewound power types.

 

Ok guys, thansk for all the help. i made 2 light bars so far. one was a little over a foot with 14leds, worked perfect with two 15ohm resitors....next i made a 2-3ft bar with 27leds. theres one thing you guys didnt inform me about.

Apparently Ohms law isnt Linear because as i increased the number of Leds i used the resistance requirement increased. According to Ohms law i should only need 10ohms resistance for 27 Leds. Well since Ohms law isnt linear and it sort of curves with increased amps, i needed about 60ohms of resistance without frying a 10 ohm resistor. can anyone help explain ohms law to this extent?

 

Do you have any pics of them HamSpiced? After reading through this post for some STRANGE reason, for I have no idea AT ALL what you guys are talking about, I'm rather curious to what it looks like. Thanks

 

Well basically this post was trying to explain how to get the proper resistance for the LED's to work...I got a long piece of 1/16th thick posterboard and lined leds across it about 1.5 inches apart. then i basically tacked it to the back of my amp box. I took some pictures tonight, i have no idea when ill be able to have them up on the boards. so ill just say ill have them up as soon as possible.

 

That sounds like it might look cool, can't wait to see them!

 

Ok you asked for em, here are they are in the box.

 

Heres with the box open @ day.

 

im gonna put them on my cardomain site soon so you can check there for more soon.

www.cardomain.com/id/hamspiced