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I want to power a single led with a power supply from the wall. I use just a single blue led for a lunar light. Anyway, how it runs now is the led is a 3.8v and it is connected to a resistor, then to some lamp cord like copper wire, and then to a 4 "AAA" battery holder with on/off switch that i got from radioshack. It works and looks awesome but I dont want to keep using batteries to power the led since it will cost a lot to keep changing batteries when i want to run it on average 6 hours a night. It is just my little diy project i am trying. I just want to know how to wire the led to a power supply to the wall. I know nothing about electric as far as that. Like can use a cell phone charger or some other type of plug? I don't know. Just tell me what parts i need and how to do it. I have a soldering iron so i guess thats a plus.
 

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ok i'll take a look while waiting for any answers here. So far i found an old phone wall charger i dont need. It says on it "Input: 100-240 VAC 50/60hz 0.15A Output: 5VDC 0.35A" Would me cutting this and wiring it in like a battery holder be the only thing i need to do and would this be safe and work? I would change the resistor since i am going from 6v to what i think i understand as 5v.
 

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Are these real?
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You will need a multimeter to measure voltage. You can get them for $2 - $8 at Harbor Freight Tools, or for a bit more at Sears and such.

Then you need a DC wall transformer/power brick/etc that outputs 5 to 6 Volts. There are many computer/phone/USB related things that supply 5 Volts, so you might have something sitting around.

Some of the chargers that say 6V actually output more than that (perhaps 9V) which might or might not overload your LED. That's where the multimeter comes in to verify the voltage.

One thing you can do would be to visually compare the LED brightness when connected to batteries vs connected to the charger. If it is similar, you (and the LED) should be good.

Edit - Your 5V phone charger should work well. If the voltage is 5 or 6V you might not have to worry about the resistor, just leave it in place.
 

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cool, thanks. Should i still get the multimeter to make sure it is correct? How do i tell which of the 2 wires on the charger are positive and negative? Is this relatively safe to do? Like this wont start any fires or electrocute me, right? lol
 

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Algae Grower
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do you have an old cell phone charging cable? it's probably real close to the voltage you need. i made a diy moon light with a 1w led stolen from a flashlight and a motorola cell phone charger. works great.

 

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Children Boogie
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you can always go back to radioshack for a AC to DC 5v adapter too. it should be $4.

slice up the wire. One should be positive (black I believe), the other negative (white). Connect the resistor to the positive, then the LED then the negative wire.
 

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The answer is you can power the LED from any power supply you want, LED's are current mode devices not voltage devices. We first need to figure out how much current the led takes. to do that we need to figure out what the ohm rating of the resistor is. there should be a set of color bands on the resistor can you tell me what they are, order is important. once we have that then we can figure out that resistor you need for the new voltage adapter that you have.
 

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good point it's a diode leD, also you can use an AC wall plug it does not have to be a DC plug. AC will flash 60 times a second but you will not see it unless you move it around very quickly in the dark.
 

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Ok, I am going to use the phone charger i have that says 5v output. I have a 150 ohm resistor and after doing calculations I would need a 60 ohm resistor ideally. Well I'll try it out. Is it safe to plug in the phone charger with the wires cut and spliced? I'm guessing just don't touch the ends with the bare exposed wires, correct?
 

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LEDs can be run off of batteries partly because as the current rises the voltage from the battery drops, due to resistance of the battery. When you connect a LED to a power supply, like what is used to recharge a battery, you don't get that beneficial effect, and it is very easy to rapidly burn out the LED. You need to learn more about LEDs before tackling this, in my opinion.

Look at my thread about LED aquarium light building and I think there are some references to basic knowledge about LEDs. Just be prepared to buy replacement LEDs as you experiment with doing what you want to do.
 

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also you can use an AC wall plug it does not have to be a DC plug.
That's not a good idea. In most cases, you'll exceed the maximum reverse voltage rating of the LED, which is usually quite low (~5V).

If you are using an AC supply, a slick idea is to use 2 LED's connected in parallel back-to-back (the anode of one connected to the cathode of the other). Then wire the current limiting resister in series with the pair, and hook the whole thing up to your supply; i.e., one line from the AC supply goes to the resistor lead that's not connected to the LED's, and the other line from the AC supply hooks to the parallel LED's junction that's not connected to the resistor.

Ok, I am going to use the phone charger i have that says 5v output. I have a 150 ohm resistor and after doing calculations I would need a 60 ohm resistor ideally. Well I'll try it out. Is it safe to plug in the phone charger with the wires cut and spliced? I'm guessing just don't touch the ends with the bare exposed wires, correct?
LOL, relax. Those chargers are "Class 2" power supplies, and are inherently safe - the voltage is too low to shock you, and even if you directly short the two output leads together, the current is too low to cause a fire.

The suggestion to get a multimeter from Harbor Freight is a good one. Measure the voltage across the resistor, and use Ohm's Law to compute the current. You want it to be approximatelty the nominal rated current for the LED. If you don't knw what that is, about 20 milliamps (0.02 amps) is a good number.
 
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