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hi would this work if i used 5 12v Leds(parallel) and connected 3 9v pp3 batteries(parallel) for power, also would the LEDS need there own resistors each? look at image for detail

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bonsoir, déjà les piles seront en cours circuit vu qu'elles sont en parallele
(désolé je ne parle pas anglais)

LED's (light emitting diodes) are just like any other diode in that they have what is known as a forward voltage drop. Typically they are around the 2 - 3volt range.

You need a series resistor to do two things:

- drop the rest of the voltage (not dropped on the LED)
- reduce current

For example, if you had a 12v power supply / battery and connected the negative end to a 1kohm resistor, then the other end of the resistor to the LED cathode, then the LED anode to the positive end of the battery you would know have a complete circuit.

Lets say that your LED has a forward voltage drop of 2volts, this leaves 10volts for the resistor (10volts dropped across the resistor) now we can work out the current flow using ohms law.)

So If we do the voltage dropped over the resistor divided by the resistance then we get:

10v / 1000 ohms = 10mA

And in a series circuit, current flow is equal - so the current flowing through the LED is 10mA.

Lets say that you kept this original circuit and then added one more LED, connected across (or in parallel with) the orginal LED. You would still have 10volts across the resistor and therfor you still have 10mA total current. but now that there are two LED's, the current would split up and you would get 5mA flowing through each LED (so they would be about half as bright as the single LED.

There are no such thing as 12V LED's. It means that the LED tops out (fails) at 12v which is a very high power rating. Either your are getting your information from radioshack (has so called 12v LED's but aren't) or wrong information.

I do not know exactly the answer (as I'm not familiar with 12V LEDs) however I've had great results with the LED series/parallel array wizard here: LED circuit wizard

Just put in your source voltage, LED voltage requirement, LED current drain and number of LEDs, and it'll suggest a layout and tell you the resistor values.
Hope that can help!