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A light bar can brighten your house through the use of ambient lighting. You can lighten up hallways, add a fading glow effect behind your entertainment center, create new patterns in light graffiti or simply add a light source to your house. There are endless possibilities for lighting with a light bar, it's all up to you!

The parts are fairly cheap and the project is fairly easy. You will need to strip wires, solder leds, and be able to use a power drill. With LEDs cheap and long-lasting this project will add a warm glow to your house.

Once you have purchased the parts you need (You likely have most of them already) actually putting the bar together should take about 3 hours (if you are inexperienced).

This instructable is designed to teach with pictures as well as words. Most of the pictures have notes added to them with tips and information.

*** I am not liable for any injury, property damage, or any other losses that happen within this project. You will be working with electricity and should be careful. Though the voltage and amperages I used in this project are not harmful (or even be felt), using a more powerful electricity source, and the use of hot objects (Soldering Iron & Hot Glue Gun) can cause damage. ***
 
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Step 1: Parts & Tools

The pieces needed for a LED bar are reasonably cheap. Don't be alarmed at the amount of parts needed - nothing is expensive, all of them are pretty common and easy to use. You probably already have 3/4ths of this stuff right now.

Most of these parts were purchased at The Home Depot and Lowes.

Metal Wire Cover (Light Bar) $5.00 for (1) 5' bar. Used to keep people from tripping over wires in the home or office, I modified it to become my light bar. You could also use wood, PVC pipe, or another material. (Though I suggest something compact and tidy).

Rubber Insulated Clamps (3) $1.25 for 2 - These are used to mount the light bar to a surface.

Electrical Tape (1) $4.00 for 66' - Used to hold pieces together and insulate wires from bar.

Wet Rag - Any cloth or sponge will do, just soak it in water, its used to clean leftover solder off your soldering iron.

LEDs (18 for one light bar) $10 for 100- Pick whatever colors you want. I also suggest fading LEDS. You can use any voltage you want, though most colors fall in two categories, 1.9-2.1v(red, orange,yellow), and 3.0-3.4v (green,blue,white). Brightness is up to you, 10000mcd-18000mcd (Millicandelas) are plenty for night lighting, something like 25,000mcd may be too bright for night time, but good for accent lighting (glowing under furnitur, though 35,000mcd or higher can even be daytime lighting. Real life stores are far too expensive, so on EBay you can get them from Hong Kong for 1/20th the price. I suggest the sellers HKJE LED or LED-HK

Hot Glue Gun $5 - Get a lot of glue sticks, as they will hold things in place and insulate.

Power Supply (1) $1- Any source of power will do, though LEDs run on DC. Your voltage can be whatever you want, but you must choose your own resistors. (Supply Voltage should be higher than the LEDs Forward Voltage, around 300mA for one light bar (Milliamps are the max amount of LEDs you can have). I got three supplies for $3 at my local GoodWill charity.

Resistors (At Least 10) $3 for 100 on EBay, I suggest ResistorsPlus- These keep the LED from taking in too much electricity. It can change a 9 volt or 12 volt power supply into a 3.3 volt for an LED. For my 9 volt supply, I needed 150 Ohm resistors (9 Volts for 2 LEDs in Series). Calculate yours @ ledcalc.com A common rating is wattage, this simply means heat dissipation, you can always have the W number higher than recommended, but never lower. A higher wattage rating costs a tiny bit more, and is larger, for the most part 1/2 watt is fine, unless you begin using ultra-high power LEDs (like Luxeon Stars which can need 3-10W resistors). 

20 Gauge Speaker Wire (Around 8-10 feet) - Used to connect the LEDs to the power supply.

Soldering Iron $10 (1) - Cheap, everyone should have one around. A 15 Watt iron from Radioshack works fine.

Solder (1) $3 at Radioshack- Solder with flux. I recommend silver solder at 0.022" thickness and a rosin core, it's easier to flow and more durable. Used to connect LEDs to the Speaker Wire.

Needle-nose Pliers - Used to bend LED legs.

Insulated Quick Disconnects (Optional) $2 for 12- This is used to easily plug the power supply into the light bar. You could just solder the power supply wires straight to the speaker wire, but then you always have the cord attached. (***Update, I now recommend using 2.5mm DC barrel plug connectors, they are much more durable, easier to plug in, and make a stronger connection. Buying them online is semi-random, try eBay as always**

Power Drill (1) - If you don't have one, ask a friend.

13/64" Drill Bit (2) - $1.50 for one. Used to drill the holes in the light bar. 13/64th" is the perfect size for a 5mm LED, it keeps them from going through the hole and holds them in place.

Wire Clippers - Used to cut the legs of LEDs. You can use some small scissors as well.

Awl - Something sharp with a fine point. I'm sure you can find something.

Scissors - Used to cut speaker wire and electrical tape.

Wire Stripper or Knife - Used to strip plastic insulation from the speaker wire.

If you are new to LEDs or soldering, I suggest viewing this guide @ llamma.com

Step 2: Light Bar Material

Picture of Light Bar Material
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What I used for my light bar is a metal wire cover. It is designed to stuff wires into to keep people from tripping over them and yanking everything out. I chose metal because I wanted something durable and all in one piece.

You don't have to use metal like I am, or even a wire cover. If you can find a piece of wood and drill holes through that, awesome! Plastic wire channels work even better, and are much easier to drill through. I chose this because it's cheap, I was unexperienced when I made this guide, and I wanted the bars rigid, today I suggest plastic channels, don't get the thin ones though.

For mine, it has a metal clip that is just smashed on top of the bar. Just push on it with some pliers to pop it out.

Step 3: Mark and Measure

Picture of Mark and Measure
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Mark the LEDS

Light Bar = 5 feet = 60".
Take off 2" on each side for the Insulated Clamps and connectors = 56".
9 Modules of 2 LEDs each = 18 LEDs.
56/8= 7" of spacing. (We divide by 8 rather than 9 because 2" is the where the first module goes).

For a light bar 5 feet long, each module should be spaced 7 inches apart. Get a measuring tape or yard-stick and with a pencil mark these slots for a 5' light bar.

2"
9"
16"
23"
30"
37"
44"
51"
58"

Now the LEDs should be spaced 1 inch apart. So at each of the previous marks, measure 1/2" on each side and make a plus with a pencil (Try to put it near the middle of the width of the bar). This is where each LED will go.

Measure the Length of the Speaker Wire.
This is fairly simple. Just stick your wire along the bar and measure out 8 or so extra inches. These 8 inches make up for any slack within the bar, and provide extra wire to connect to power supply. When you are finished, you'll just cut off the extra anyways.

Pull the two speaker wires apart from each other, we want them to be separate (see picture).

Step 4: Measure Twice, Drill Once

Picture of Measure Twice, Drill Once
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There are a couple ways you can go about putting the holes into the bar. You could just use the drill bit and inaccurately drill through the bar. However this takes far more work and is more tedious than it should be. This is where the awl comes in.

Remember the marks we made on the inside of the bar? Well, take your awl (or another sharp pointy tool) and put it on the line you drew for a LED. Try to line it up with the middle of the bar and smash the awl with a hammer. Initially you should make a dent and punch a very tiny hole, later you will punch a small hole back through.

Flip the bar over, and put the awl on the new dent pointing towards you, and smash it downward to leave a bigger dent (this is thanks to metal fatigue). Hit it until there is small hole (less than the width of an LED), and use your 13/64" drill bit to clean it up.

Repeat 18 times for 18 holes, and then we will prepare the wire.

Step 5: Power

Picture of Power
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Power Supply
Your power supply can be from pretty much anything. An old PSU from a computer, a leftover hard drive power brick; I prefer small and compact power supplies such as those in cordless phones. Laptop power supplies are an amazing power source, they are super cheap and available, usually can supply 3-5 amps (which means a max of about 230 LEDs), and are regulated [which are normally super expensive] at 12v DC. No matter what the plug on the end is, you can bet there are two wires in there: Positive and Negative.

I obtained three 9 volt power supplies at my local goodwill for $3. eBay also has a plentiful selection of power supplies, though it will take some searching. The supply needs 350mA or more to power 18 LEDs. mA determines the maximum amount of LEDs. 99% of 5mm LEDs use 20mA each, so just multiply the number of LEDs by 0.020A (18 LEDs * 0.020A = 360mA, which is technically overloading it, but it still works). 

The speaker wire will carry the electricity from the power supply wires to the LED wires. Decide right now which of your two speaker wires will be your positive, and which will be your negative.

As a general rule, the red, yellow, white, or lined wire is the positive, while the solid (usually black) is negative. After the next step, you will have two LEDs and a resistor soldered together. Just try touching them both to the speaker wire, whichever lights up for you is your correct solution.


Quick Disconnects
This step is optional. It makes it easy to plug and unplug the light bar from the power supply. If you don't want to use Quick Disconnects and want the power supply always attached, just twist the wires of the speaker wire and the power supply together and solder them. Wrap them with electrical tape to keep anything from shorting out.

Quick Disconnects have a wire going into them, and usually you just crush it with pliers (Called crimping) and the wire stays in place. An optional purchase to skip this awl & solder method is a pair of crimping pliers. Regular pliers were incapable of doing the job for me, so I pierced and soldered them into place. Knowing from experience now, I strongly recommend just buying crimping pliers than this next awl + solder method. If you don't feel like spending money, then go for this method, which actually is a stronger connection than crimping alone.

Because its not possible to stick solder into the Quick Disconnect (its covered in plastic) and melt it and the wire together, you should coat the end of your wire with solder. Stick the wire into the quick disconnect. Now hit the Awl on top of the Quick Disconnect, this will pierce the casing and squish the metal and wire together. Follow it up with sticking the tip of your soldering iron into the hole to melt the solder. You should have a very solid connection between the wire and Quick Disconnect. Finally, wrap any exposed areas up with electrical tape.

Step 6: Snip, Sheath, & Solder

LEDs like the ones we are using in this project have two legs. A positive long leg (and a skinny head), and a negative short leg (with a bulky head). The resistor attaches to the front positive leg (see picture) and the resistor is soldered to the positive speaker wire. The purpose of the resistor is to keep the LED from getting overloaded (they will without one, and become very hot and burn out permanently).

Use the pictures as a guide.

Soldering LEDs Together
Bend the legs of each LED to 90 degree angles. Clip the front positive leg so it is short , this is where the resistor will be attached. These are wired in a Series, meaning the LEDs legs meet back to back (postive-negative-positive). See the diagram for a visual illustration.

Set the LEDs into the drilled holes, as this keeps them aligned and pointing in the same direction. Make the legs meet, and touch the soldering iron at the meeting point. Touch your solder to the legs, and it should melt onto the legs binding them together. Now bend the front positive leg into a U shape, repeat for the resistor. This hooks them together and makes it easier to manage. Solder them together.

Soldering LEDs to Wires
After the resistor has been attached to the front positive LED, remove sheathing from the positive speaker wire, and solder the leftover resistor leg to it. Then remove sheathing from the negative speaker wire, and solder the negative LED leg to it. You can now test if your LEDs light up by plugging in your power supply.

Securing/Insulating with Hot Glue
Place the LEDs and the newly attached wires into the bar, and the LEDs go into the holes. Make sure that no LED legs or exposed wire is touching the bar. The LEDs and wire will naturally want to move around, so press the LEDs down with pliers so they are flush with the holes, pour on a lot of hot glue, and wait for it to dry.

Repeat this step 8 more times, and then its time to finish everything up.

Step 7: Finishing Up

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Hopefully all your LEDs light up, your power supply has a solid connection to the speaker wires, and the hot glue is holding everything in place. Now its time to finish this light bar.

If everything is set on your light bar, snip off any extra cord handing out the back end. Wrap the end with electrical tape just to keep it together.

If you find yourself making a lot of these, a step I don't cover is called daisy chaining. Basically you put quick disconnects on both ends, so it can be powered on via either side. Then you make a short (3 inch or so) connector cable that plugs the light bars into each other end to end, this chain can go on indefinitely. If the quick disconnects on both sides of the light bar are female plugs, then your connector cable would have male plugs on both ends of it.

Put the slide back into the bar, closing up the light bar. Reinsert the friction clip to lock the slide in place. And the light bar should be completed. Now you can choose where you want to put the bar itself.

This is where the Rubber Insulated Clamps come in. I like to use screws, however nails are equally good. One clamp goes in the middle, and two on the ends. This is why we saved 2" on each end of the light bar, making it easy to attach to a surface. Pictures show how it can be done.

Optional Sanding
This is a step you can use to change the appearance of your LEDs. If you feel that your LEDs are too bright or shining too strong of focused beams, you can sand the tops of the LEDs to more evenly diffuse the light. Go purchase some very fine (600-1200grit) sandpaper and just rub the top of each LED. you should have a smooth blurred LED, and this will scatter the light more effectively.

Step 8: Mounting the Light Bar

Picture of Mounting the Light Bar
Now that you've finished your light bar, there are numerous places to put it.

I've put some behind my couch so beams of green and blue lights shine out of the back. We also screw them into the ceiling to shine down the walls for our primary lighting in our house. For LAN parties (with the red and blue rooms of the house, each with red and blue LEDs) we place them in the corners to shine along the walls for each team's room color, and green LED light bars signify the neutral room with all the food and drinks. Use your imagination to place these bars, especially with the use of refractive (glass) or reflective surfaces.

This guide was focused on a 5 foot bar, but any size will work. If you have any improvements upon my methods, or great ideas on how to use a light bar, feel free to leave a comment.

Happy lighting - QuackMasterDan.
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track9wv1 year ago
Is there a way to use many different colors and have some type of switch to turn each color on and off separately to create different combinations?
QuackMasterDan (author)  track9wv1 year ago
I should also add on, that this guide is rather old. Recently there are now LED ribbons that do the exact same job (R-G-B-R-G-B) as my painstakingly made light-bars. A TON easier and cheaper, eBay is your best source. It's going to be a number and a RGB ribbon, I think the 5050s SMD/SMTs were the best model I found. Hope that helps!
QuackMasterDan (author)  track9wv1 year ago
Indeed, it requires a micro-controller using pulse-width-modulation. It doesn't have to be as hard as it sounds.

I previously was working on an Instructable for this exact project, but I got tired and never finished writing it for publication. There is enough in there to figure it out with some work, and it's a good start.

It is located here: http://www.instructables.com/id/ESTRWXVFYTCLJ5J/
kking183 years ago
Okay so I have a quick question. How would you add a female and male audio jacks to this circuit so I can play music along with making the lights flash? Currently I have 100 LEDs and a 12V wall plug that has 1amp work of power since thats what I need to run the lights. Pleasepleaseplease help me.
kking18 kking183 years ago
Correction 50 LEDs
Definitely much harder. I have been working on it myself and to do it through a micro controller you need programming experience. And through analog you need schematic experience.
QuackMasterDan (author)  kking183 years ago
It's actually much, much harder than you would think it is. You'll need to have a programmed microcontroller (Arduino is the most common for this), which can either a) react to a microphone and turn on/off power related to volume or frequency, or b) program the microcontroller to listen in on the raw audio-feed from your computer with a serial connection. It's a pain and it's expensive since you need equipment for programming and operating the chips. Wish I had better news =[
I am not much into electronics but while going through the comments of your instructable u said that one can't connect more than 2 leds in series , then how do christmas chain leds work with a consistent glow though they are connected in series.. ? i hope u get me ..
They are actually run in parallel.
MackeFeet3 years ago
Hey..vthanks for the Ible just wanted to ask a few quick questions.. This Ible inspired be to go out and do my first led project but mine is going to be made out of half of a PVC pipe.. Okay so if I run in parrellel of I do instead of 3 bulbs per resistor it's fine to do just 1 per resistor right? And also does parrellel really drain batteries as much as everyone makes them out to be or is it slightly more than series or what? Any help is appreciated.. Thanks for the insfructable once again I'll be posting my project when I get it done and I'll probably mention you in it for inspiring me but anyone please get back to me... Thanks!
QuackMasterDan (author)  MackeFeet3 years ago
Parallel uses more juice, because more stress is placed on the resistor, which is emitted in the form of heat. There are three primary resistor wirings: single [One resistor, one LED]; series[one resistor, multiple LEDs in a chain]; and parallel [one resistor, unlimited with common positive and common negative]. Yes, parallel does drain batteries more. Wiring single-per-LED is the most efficient actually. The maximum you can realistically hit with parallel, is about 7-10 LEDs per resistor before the size of the resistor becomes ridiculous. There is a danger in parallel though, if one or more of the LEDs fails, then the power output to the other LEDs increases.

Also, funny you mention this guide, I am writing the sequel to this at this very moment. The guide should be completed in about a week, and I must say, it is turning out pretty dang awesome.

If you have any other questions, feel free to ask.
I never heard about that. Is that only if you have like 2-3 less per resistor? Or is that with one led per resistor too? Or what.. I kinda confused now.. ( I'm 13) lol also message me the Lin to the sequel when you get done too if you think bout it.. I'd love to see it.. ;) thanks!
QuackMasterDan (author)  MackeFeet3 years ago
The entire build and install was completed today. Aside from gathering parts which took about two weeks of course (shipping from China is slow). Took about 200 pictures. I need to clean up the house and make everything pretty for photos in the guide though, but here is an idea of the result.
Shiny.jpg
That's pretty sweet man.. Are those neon tubes or is it just tightly packed LEDs?
Also can you answer the question.. Because if that's a danger I'm gonna be bowing up my LEDs.. Lol..
"that" is the danger you mentioned about.. Sorry bout any confusion..
tckinlay5 years ago
hey this is a really cool. i am 14, do you think this project is suitable for me to make and do you think you could even put your idea into a water feature??
I'm 12. And im making this. Everything is ok, just i dont like the soldering :D
I'm 13.. And making this :) we should all team up us teens and make something AMAZING! Lol.. I'm making my own twist on this bar.. Be posting a Ible soon on it if you want help..
QuackMasterDan (author)  MackeFeet3 years ago
Hehe, I'm all excited now, it brings me great joy to see others building and learning and developing their skills. Be sure to link me to whatever you make. I've got sequel to this instructable, a few years of evolution in the making, that will be released within two weeks.
QuackMasterDan (author)  tckinlay5 years ago
Do not let your age hold you back, by the expectations of others or yourself, if you are interested in a project pursue it to the best of your ability. If it doesn't turn out well, you will always learn something from failure. There have been electronics pioneers far more skilled than me before they were even 14 (I'm 21 by the way).

As far as combining the light bars with water, unless there is something moving within the water, it will just look like a light is passing through your body of liquid, no different than a light-bulb or fluorescent tube. Electronics don't work well with water, and making a submersible light bar water-tight would be a lesson in failure.

There are however applications that involve LEDs and water. One of my favorites is rapidly pulsing LEDs that shine indirectly (meaning you don't see the LEDs themselves) into falling water droplets. The LEDs of red, green, and blue change color very rapidly, on par of 20-30 different colors a second. Depending on a water droplet, if it falls into the path of a LED as it is a certain color, it looks as though you are seeing falling jewels. Bigclives.com RGB microcontroller kit has  pre-programmed patterns, including one for water droplets. That's a rather advanced project for a complete beginner (more advanced on the water droplets than the lighting), but if you are interested I use his controller for lighting my apartment. Here is a link to my instructable which is currently unpublished. http://www.instructables.com/id/ESTRWXVFYTCLJ5J/

You would need to be a bit more specific by "water feature", there are a million different ways to interpret a water LED project, whatever you decide to create, make an instructable and send me a link when you are done.

Lastly, this instructable I consider to be a great beginners project, it's one of the first things I ever made electronically, explains the basics of LEDs, resistors, amperage, and voltage, and doesn't need to be precisely done. I say, go for it!
This is a cool instructable, thank you for posting it.

I have a similar question about water. I was thinking about making this to put outside behind a small glass block wall so at night the LEDs will light up the wall, but I'm afraid it will not last long once it rains. Any advice? I was thinking maybe using hot glue around the LEDs and any openings to try and make it water tight.

Also, I'm very new to electrical work, with a 9V power supply and the LEDs only needing 3ish would I be able to double the size of this and make a 10 foot bar?

Thanks.
QuackMasterDan (author)  btoast4 years ago
When comparing the power ratings of your LEDs and your power supply, use watts, not volts or amps. Watts = volts * amps.

If your 9v power supply pumps out 340mA, it would be able to supply 9v * 0.34A = 3.06 Watts.

Even though the LEDs run at 3.0v, it's easier when doing a chain of them to have the supply have a higher voltage. If you want a ten foot bar, calculate how many LEDs it would be, then add up the Watts. I imagine that would be something like 40-50 LEDs for ten feet. 5mm and 10mm LEDs run at 20mA. so 0.02A * 3.0v * 40LEDs = 2.4 Watts. Pick whatever number you want, whether it be 50 or 100 LEDs, just calculate by the watts.

Don't try waterproofing the light-bar, you will be let down and become frustrated, especially at the electrical connector (though you could just stick the wire directly in and hot glue it). By this I mean, do not try to waterproof your light bar to the point you can submerge it in water. If you're just adding extra hot glue to keep out moisture, it's better than nothing I suppose.

I've seen an installation where someone used LEDs to light up their glass block wall. First off, he didn't use dinky dim 14kmcd 5mm LEDs, but 10mm 70kmcd LEDs (kilo millicandela, a measure of brightness), and around 40 of them (three per block). The lights were placed on top of the glass wall facing downward. He had to make little risers to keep the LEDs from bumping into the glass so they could face straight down.

Though his installation was inside of a wall for a bathroom, it sounds like yours is standing outside in your back yard. To protect it from the rain, get a small piece of flexible waterproof plastic (heck, I bet scissors and a cheapy rainjacket would do), and just throw it over the light bar so the rain doesn't land on it. It shouldn't need to be very wide, just enough to cover the light-bar and touch whatever surface it is sitting on. I made a quick picture to show you what I mean. If you have any more questions, feel free to ask.
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Thanks for the quick and detailed response. Yes, the block wall is outside, and I see your diagram of having it on top of the blocks, but the blocks I am using are rounded at the top and rounded on the corners; additionally, they are held together using mortar. If I were to place the LEDs on the top, only the top row would be lit as the light would not penetrate the mortar to light the blocks below.

So, what I was thinking was placing it behind the wall and allowing it to shine up along the back of the wall, similar to what you did with the lights behind the couch. With the blocks being clear and diffused it should light the blocks up as a fade from the bottom to the top, the bottom blocks being the brightest. The issue with this is that the lights sine directly up, and thus could not be covered. Maybe if I fill the track with silicone after all the wiring is done to ensure no water can touch the wires that might elevate much risk. I don't know. I am thinking of making one just for the hell of it and seeing how long it lasts.

Thanks again for the response
sparx014 years ago
*of
sparx014 years ago
How would you go about making a rippling effect?
You know, random dimming if selected LEDs? Thx.
would i be able to use your light bar for the light sorce for this instructable.
http://www.instructables.com/id/Music-LED-Light-Box/.
and would any modifications be nessasary?
QuackMasterDan (author)  joshleathers4 years ago
You could make the light bar music reactive yes, they are a very similar design. The only difference is that you would need multiple TIP31 transistors, one per four LEDs. You can't run 18 LEDs in series, they wille be either extremely dim or not light up at all. Both projects have very similar wiring, just replace the + and - terminals of the battery with the + and - wires of the power supply. Though he is using 12v, I believe you coud use anywhere from 6-12v for the project, just make sure your supply can handle the 18 LEDs. Though I normally say to always use a resistor, I believe you do fine without them by using the transistor method.
Is it really necessary for a transistor on each of the strings of LED's? Is it possible to just do something like this (see attached pic). I assume it would be ok, providing the total power rating of the LED's doesn't exceed the power rating of the transistor.. But I could be missing something?

Thanks :)
Denno
b1b2b3 b1b2b34 years ago
Sorry, doesn't look like the pic uploaded correctly the first time. here it is now, hopefully this one works..
LEDMusicLightBar.png
QuackMasterDan (author)  b1b2b34 years ago
That circuit looks like it would work just fine. Note that I did not say to connect a transistor to each LED series, but rather a resistor (wavy line) to each LED series, just like in your image. And yes, you need to make sure the transistor can handle the power rating of all the LEDs it will be connected to. That shouldn't be much of an issue, as LEDs are low-power. You will likely need a small heatsink for the transistor.

Thank you for your input.
did u mean dat 2500 mAH is capacity of each battery?
if so then totally it will be 5000 mah but just as the capacity is lessened,it shud still remain 2500 mAH,right?
QuackMasterDan (author)  mayur.phadte4 years ago
I was correct in my statement, and yes, your statement is also correct. Adding two AA, 1.5v, 2,500mAh batteries in parallel will keep the voltage at 1.5v but add their capacities to 5,000mAh. Capacity effectively is mAh. mAh stands for milliamp hours, as a way of describing drain over time. Capacity can also refer to current, which is simply amps, A.

I threw together a quick picture in photoshop to illustrate how it works.
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But I was taught in kindergarten that Series=voltage divider in ratio of resistances
Parallel =current divider in ratio of resistances
wat about that?
I am not pointing out anything wrong but trying to learn something.
not arguing but trying to turn this into an informative debate.
Sorry If I hurt you in any way
:P
QuackMasterDan (author)  mayur.phadte4 years ago
Your are correct, but note that those statements apply to the wiring of resistors together. Demand from the LEDs (in terms of volts and amps) remains the same, no matter how much power you provide them, they will take as much as they can use. The LEDs conduct through one another in series, so yes, with each LED in the chain a bit of power is lost through light being emitted. This becomes a problem when you go beyond three LEDs, where the fourth can be noticeably lower than the first. Within just two LEDs, the loss of current from LED to LED is low enough to not be noticeable.

As far as series being a voltage divider, and parallel being a current divider, yes, that is accurate in both terms of supplying power from a power source (generally that refers to batteries), and the wiring of resistors. It works both ways, not simply reducing as in division. If you add power sources (batteries) in series, the voltage *multiplies* (or you could say, divides by a ratio below 1:1) If you add power sources in parallel, the capacity for amperage *adds* while voltage remains the same. This is very useful when trying to get extended battery life from your power sources. Here is an example.

Let's say you have a Luxeon LED Star that runs at 3.0v and 700mA. You have two AA batteries, each which puts out 1.5v and has a capacity of 2,500mAh (milliamp hours). If you were to add the two batteries in series, you would double the voltage at the cost of halving the capacity. So you would get 3.0v but now only 1,250mAh. If you have four AA batteries, you can have the the benefits of both, at the cost of greater physical size. If you have any more questions, feel free to ask.
I dnt really agree with 18*20=360ma thing
With 12 V DC u connect 4 LEDs in series,right?
so they share the same 20mA
So technically every 4 LEDs share 20mA.
SO u could run about 18*4=76 LEDs on that thing.
Correct me if I am wrong
QuackMasterDan (author)  mayur.phadte4 years ago
Power drain does not work like that. For one, the LEDs are in series of two, not four, which makes a large difference on the amount of stress put on the resistor. Second, the resistor chosen with the ledcalc calculator has been calculated to allow two LEDs in series to receive 20mA each, so in reality, the resistors are allowing 40mA through, in which each LED consumes 1/2 of the power.

The hard limit for how many LEDs are allowed is calculated in watts. To calculate watts, it's simply amps times volts. So if your power supply pumps out 350mA at 12v, you have 0.35A * 12v = a 4.2W power supply.

Let's count the drain for one LED, a green 5mm running at 3.2v and 20mA. So 0.02A * 3.2v = 0.064W. Now, let's divide the drain of an LED into the capacity of the power supply, which is 4.2W / 0.064W = 65 LEDs. 65 is the ideal limit, in reality, due to heat and resistance and other inefficiencies, power supplies need a bit of buffer room, so let's just cut off a few LEDs, and say the realistic limit is 60 LEDs.

I hope that makes sense, if you have any more questions, feel free to ask.
brigs1644 years ago

i was wondering if a 12v 1amp dc plug would work if im hooking up 5 bars together
QuackMasterDan (author)  brigs1644 years ago
To measure maximum power possible by your power supply, you need to measure everything in Watts. A Watt, is simply volts * amps.

So if you have 18 LEDs on your light bar, with each LED running at 20mA (milliamps) and 3.2 volts.
18 LEDs * 20mA = 360 mA.

Then let's turn that into Watts
3.2v * 0.36A = 4.32 W.

For five light bars
4.32 W * 5 Light Bars = 21.6 W
Realistically, we want some buffer power since real electrical drain isn't perfect, let's just add 5 Watts to be safe. Thus, 26.6 Watts is our power drain.


Now for what your power supply can put out,
12v * 1 Amp = 12 Watts.

Sadly, that power supply cannot provide enough juice to five light bars. It will realistically be able to light three at full brightness, and at three, it will become extremely hot (like, burn your finger hot, which is bad). So the safe amount for that power supply is two light bars.


If you want a cheap power supply that can handle a ton of light bars, go find a laptop power supply, They are usually in the range of 50-75 Watts, and can be found for a couple dollars at a Goodwill, or bought on eBay for $13 including s/h.

Good luck.
vj034 years ago
Great idea and tutorial!
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