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How can I make something work on "Wall power", and where to buy cheap LEDs?

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thejuggla1

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First off this guy at work wanted me to make a LED light bulb, but I looked online they sell for like $5 for like a bulb that has 20 5mm LEDs, so there's no point, however he might want it a lot bigger so I might be able to do something for him still.


I have made a strobe light that plugs into the outlet at school, but I am not exactly sure what lets me plug that project into the wall and why the rest I made were designed to be battery operated. How do I make LEDs work off the 110V power coming from a house? Power coming from the house is AC and LEDs use DC correct? I couldn't just group like 60 LEDs in series and throw in a resistor then? The only thing I've tried so far is an old computer power supply, but I question how safe it is because it is old and not sure if tampering with it can cause problems.(What I did was cut the 5V wire and a ground and plug 2 LEDs + Resistor into it and it worked fine) I seen some LED drivers while browsing the web, they look like something I should use for something like this?


What is all the Specs on LEDs mean? I know what they are but not sure what they mean an example off ebay:

SPECIFICATIONS:

* Source Material: AlGaInP !
* Emitting Colour: 5mm 60° 5-Chips 0.5 Watt High Power Red LED
* LENS Type:Water clear
* Luminous Intensity-MCD: Min: 70,000mcd Max: 80,000 mcd
* Reverse Voltage:5.0 V
* DC Forward Voltage: Typical: 2.0 V Max: 2.4V
* DC Forward Current:100mA
* Viewing Angle:60 degree
* Lead Soldering Temp:260°C for 5 seconds
* Intensely Bright

Now I know 5mm is the size, 60° is the viewing angle, and I think the mcd is the brightness rating. Now this (Min: 70,000mcd Max: 80,000 mcd) really means nothing to me to tell me how bright it is. What is a good MCD to look for?

If say I bought a 15° Min: 70,000mcd Max: 80,000 mcd compared to 60° Min: 70,000mcd Max: 80,000 mcd the 15° is brighter because it is more concentrated correct? But would grouping a bunch of 60° give me better area coverage? What would be a good mix between Brightness and Viewing angle for lighting?

What does the Reverse Voltage mean? Ex.
"* Reverse Voltage:5.0 V"

Is there any places that sell cheap but good LEDs that you guys know of?
 
Reverse voltage means the maxmimum the Light Emitting Diode will take before breaking down and allowing current the other way.

As Wall Power supplies are AC, that means the LEDs will blow almost immediately as AC goes "backward".

You'll need a rectifier. And probably a transformer, unless you feel like wiring tons of LEDS in series.
 
Well I am guessing a rectifier converts AC to DC, and vise versa? Is there a schematic of how I would build one? As well as a transformer? Just wondering could I group a few LEDs in series followed by a high ohm resistor once it is switched to DC or does it not work like that at that high of voltage? Any disadvantages of grouping large ammounts of LEDs in series?

Also how do you check to get your resistors right with the LEDs? I remember being told taking a Multi Meter and putting it before and after the LED and using some formula to tell if the LED needs more/less resistance?

Also have a little lego collection(Built a few operational traffic lights, light posts ect.) that I would like to run off an house hold outlet so I will definitely be interested in building it for myself.
 
I don't think you know enough about electricity and electronics to avoid electrocuting yourself and maybe other people. You don't even know the basic formulas of Ohm's Law.
Buy a light instead.

An LED with a viewing angle of only 15 degrees is a cheap old dim one in a focussed case. It is almost useless unless you are making a spotlight.

CHEAP (Chinese) things work very poorly for a short time before they fail.
 
Don't have much knowledge I admit, took 2 electronics classes in high school. Don't remember a lot of the book work, all I can really remember is how to read a diagram, a couple formulas and the Resistor Coding. I did all the troubleshooting/projects flawlessly however, pretty sure I remember being at least top 3(Think I also got 100% one term) I just forget a lot of the book work stuff. Just started my first day of my electrician schooling today so hopefully I will learn/remember some useful stuff to help me.

I am just getting sick of small time DC projects they are getting boring. I have lots of lego with LEDs to make it look like street lights/traffic lights ect.(4 way traffic light that works similar to a real one, this was a home project I did by myself btw, not something I took home from school) and want to set it up to plug into the wall with the Rectifier and lower the Voltage with a transformer as the other guy said.

I mean even with my car stereo, I started out small to get a feel for it. Now I am rocking 1000W of subs, 500W of components, rear battery with isolator, upgraded grounds and alternator positive, fused, proper gains using a Multi Meter. All installed myself with just reading stuff on the internet/using any knowledge I had. I mean I'm not someone who has no idea what hes doing and wants to make a bunch of stuff with little to no research on it.
 
You don't know enough about electronics to design a simple circuit. Maybe you can find and copy a circuit on the internet that works properly (many don't) and does what you want.
 
check out my video on how to wire a LED. With the way you want to power the LED's you will have to make a DC power supply, the basic parts of a power supply is a step-down transformer and a bridge rectifier. The step-down transformer will step the voltage down from 110 volts AC to your desired AC voltage, then the bridge rectifier changes the AC to DC. If you watch the video you will know that an LED will have 0.7 volt drop, that means that one LED takes up .7 volts, so you want to make sure that you have enough voltage to power the amount amount you choose. for example say you have a step-down transformer that steps the voltage down to 12v, NOTE: the bridge rectifier will drop the voltage by 1.4 volts, so we have 10.6 volts going into our circuit. if you divide 10.6 by 0.7 then that will give you the maximum amount of LEDs you can use in the circuit.

 
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Boy oh boy that video is WRONG! The author should be hanged or shot.
1) No LED has a forward voltage of only 0.7V. A rectifier diode has a forward voltage of 0.7V but does not make light.
A fairly old red LED is 1.8V to 2.2V.
An old green or yellow LED is about 2.2V.
A blue, bright green or white LED is about 3.5V.
 
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Seriously I am just here to learn I don't understand what this hostility is about. I guess you could say I just copy a diagram off the internet and hope it works, but I actually learn how the parts work in the progress. Like the traffic light I made, sure I didn't know what the cmos 4017(Think that's the model number I used) and was just basically following the diagram, after putting it together however I understand how it sequences each pin letting the proper lights light up to make it look like it is sequencing a real traffic light with the help of transistors.

I guess you could say I don't know enough about electronics to design a simple circuit because I don't know what every part does, the few ones I do know what they do of course I could.

Thanks for the video but I know all that stuff already.

The rectifier looks pretty straight forward to make, just 4 diodes.(And for the record I understand HOW it is doing that too, not just looking at a diagram and copying it.) I also read I should put in a capacitor to 'smooth' it out and because the capacitor can hold a dangerous charge I also read to use a 'bleed resistor' to discharge it. I am not sure about the resistor, if I connect it parallel with the capacitor it should drain it when it is off, but will it be draining the capacitor when the circuit is running? Is a 1ohm resistor enough for this or should it be higher?

The diodes have certain ratings on them correct? Obviously I cant use something that draws hundreds of watts off 4 small diodes, I have to buy diodes that can handle the wattage I am drawing correct? Since I have a bunch of little lights ect. I want to connect together, is it possible to use my Multimeter to determine how many watts everything is drawing. I can use the formula for single LEDs, but I am not sure how much my traffic light draws.

So the current must be AC to set the voltage down or up correct? So I must put the transformer before the bridge rectifier?


Although I don't need to, how to you convert DC back to AC? Sorry my logic is kinda bad; but the bridge rectifier ISN'T backwards compatible right?
 
As well I am still confused about the reverse voltage on LEDs. If the Reverse Voltage is 5V it just means I can put up to 5Vs before it burns out?(obviously a 2.2V LED is going to burn out quickly running at 5V anyways)


And for that video, isn't the formula you are using wrong? I thought you used R = (VS - VL) / I , not just guessed with a random Resistor?
 
Its pretty easy to get bulk LED's at certain electronic stores. The store i work at sells individual ones for $1, 10 @ 9$ and i think 100 @ 30$. You also have the option of getting LED prepackaged in a housing with 5 LED that run on 12V (W/O the resistors required) that are relatively compact.

Now depending on the design you choose, you can either build a cheap regulator for 5-12 volts with a 78XX or just buy a Dc power adapter for 5-15$ depending on how much current you want.
and remember White LED's use 3.3-3.5V to bias the junction.
 
There's only like 1 electronics store that I know of around me. They weren't really helpful in supplying me with the specs of the LED, I mean they had specs for some of them but not all, so I didn't bother buying any from except for just mini projects.
 
That's unfortunate. There's about 5 in my area in you include franchises, tho some time some driving to get to. You can also try certain hardware store (like Canadian Tire) for car headlight LEDS
 
You do not need a "bleed" resistor if the voltage is 60V or less because then will not electocute you.
A 1 ohm resistor is very close to a dead short. Simply use Ohm's Law to see the extremely high current in it.
The max allowed reverse (backwards) voltage across an LED is 5V but then it does not light. An LED lights with a forward voltage.
The forward voltage is not carved in stone. Some yellow LEDs are 2.0V andf others are 2.4V even if they have the same part number and are made by the same manufacturer. The series current-limiting resistor smooths the different currents.

The video is completely wrong and should be burned.
 
You do not need a "bleed" resistor if the voltage is 60V or less because then will not electocute you.
A 1 ohm resistor is very close to a dead short. Simply use Ohm's Law to see the extremely high current in it.
The max allowed reverse (backwards) voltage across an LED is 5V but then it does not light. An LED lights with a forward voltage.
The forward voltage is not carved in stone. Some yellow LEDs are 2.0V andf others are 2.4V even if they have the same part number and are made by the same manufacturer. The series current-limiting resistor smooths the different currents.

The video is completely wrong and should be burned.

I agree fully and completely
 
Not only that, the forward voltage is different for every level of current, for example, the same led could be 2v @ 100ma and 2.5v at 350ma.

There is absolutely no reason you should be rectifying and regulating the mains voltage. Go to eBay, search for "19v AC adapter" and splurge 6 or 7$ on a 3 amp model. Then you will be dealing with 19V DC. A lot safer, A lot less hassle.

For the record, you can run LEDs straight from the mains (but don't please). They are diodes and will act as their own rectifiers. Take for example, 10 HB white LEDs that you want to run at 3V 300ma. That's 30V, obviously you need something to limit current and drop the other 90V (for the U.S. 120v). 90 / 0.3 = 300. So we need 300 Ohms of impedance. For 60hz mains, that would be approximately an 8.8uF capacitor. So an 8.8uF capacitor in series with the LEDs produces the desired result. What you would not want to do, is use a 300 Ohm resistor, because it would have to dissipate 30 watts.
 
Now depending on the design you choose, you can either build a cheap regulator for 5-12 volts with a 78XX or just buy a Dc power adapter for 5-15$ depending on how much current you want.
and remember White LED's use 3.3-3.5V to bias the junction.

How does the 78xxs work exactly? I am reading a bit about them, they always put out the same voltage no matter what gets put into them? (7805 puts out 5V, 7806 puts out 6V ect.)

Think I might just got with an adapter instead, seems a lot easier then messing around with diodes and step down transformers.(Plus making your own step down looks a bit complicated and unsafe) I can probably get one that meets my needs at my electronics store? When buying how should I calculate how much I need? I am not sure how much those traffic lights draw(555 3017 and 12 LEDs) is there anyway to check its power consumption? Do I just use my Multi Meter to check the amps, then times the amps by the voltage and that should give me the wattage?

So say my lego collect is running40 White LEDs, they are about 3.5V @ 20mA(I think that's what they said they were, lets just go with that for now) so I calculate the wattage(Which is (3.5 x .02) x 40 = 2.8 Watts correct?) I would want to buy an adapter that does about 3 Watts(Leave a little room for inaccuracy of LEDs) and puts out the voltage I want correct?

Alright say I run 12Vs to my 'lego lights', the Traffic light I made runs at 9V, I can use a 7809 to lower the voltage just for the traffic lights to 9Vs. But little confused about the 3 Pins, how are they wired up? I also read the 79xx do the negative, but for here I just need the 78xx models right? These are like the transistors NPN or PNP right? They kinda confuses me, I know what you use it for, but not sure why you would need one that has two negatives or one that needs two positives?

Edit: How does the capacitor to lower the voltage? I thought they just took in the voltage they were given? It is different if you series them with the LEDs I guess? How are you calculating the size of capacitor need?
 
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