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I Can't Get My LEDs To Light Up ? Answered

I ordered these LED: http://www.amazon.com/gp/product/B0081IC18W/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1
And I cannot get any of them to light up, can someone explain a basic LED circuit to me and what batteries i need to use to light up 4 LEDs.


All of these answers are awesome. The only thing I would add is that you asked for an explanation of a basic LED circuit. The most basic LED circuit Includes one LED, a battery, and a resistor if your battery is more than 3 volts. The positive side known as the a node side usually has a longer leg. It connects directly to you battery positive. The negative or cathode will either connect directly to the negative of the battery, or to a resistor if necessary. Then the resistor connects to the battery negative. This seems to be a pretty good explaination of multiple LED circuits http://wiki.nuigroup.com/How_to_Wire_LEDs

If you place 4 led's in a ROW-- that is called a SERIES circuit. Each led needs about 3 volts to light up. So if you place 4 led's in a row, that would be about 12 volts minimum to get them to light up. ALL of the leds have a proper polarity to them. EACH led must be connected with the plus and minus wire connected properly in a +-, +-, +-, +- type of configuration. IF ONE OF THEM IS BACKWARDS, then none of them will light up. Also, you must have a resistor connected with them to limit the current to about 20 milliamperes. A 200 ohm resistor might do it. Put a milliamp meter in series with them to be sure you are limiting the current to about 10 to 20 milliamperes. It helps if you know the specifications of the LED's. Some led's are the old style that have only 0.7 volts across each one. The newer LED's have about a 3 or 3.3 volts required per each LED. You also have to be sure to connect the LED's to the battery + or - terminal properly or they might burn out instantly. The example given by "iceng" shows a good method of using 2 leds per series string that way, you can just use 9 volts, and to light up 4 LED's, just have another 2 in a row like his schematic shows. If you put all 4 in a single row (series connection) it would not light up because 9volts is not enough voltage to overcome the 12 volts total of 4 led's in a row.


4 years ago

Here you go.


So you purchased an assortment of LED with no specs!?

Typically 5mm LEDs need about 3V to work. Make sure you have the anode and cathode connected to the power source correctly and they should light. If you use a 3V battery pack you should be able to test them without using a resistor.

As for connecting 4 of them you need to know what the forward voltage of the LEDs is and the forward current. Then decide what power source you want to use. Plug that info into an online LED calc and it will give you the schematic you need and resistor values needed to make those LEDs work with your power source. Here is a hint. You will want the power source to be larger than 3V.