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# How would i used a joule theif and power 10 to 50 led on a circuit if i used a 5v power supply or a battery.? Answered

I wuld like to make a banner out of leds for my wife and i am wondering if it would b possible to do it using the joule theif method but instead of a battery use a 5v power supply. wat resistor wuld i need and is it even possible?

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## Discussions

What color LED decides how many in series and the resistor ?

A 12V supply or wall wart gives you more options.

The joule thief is really sucky for a banner.

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I want to b able to use at least 50 led's.....but i know ther is a way to increase the voltage across the circuit.....i dont necesarily want it to b simple

You increase voltage at the cost of current

Here is a sample inverter capable of running LEDs

Still what color are you planing to use ( do math for you easy to see ) ??
or do you plan to mix LEDs ( where I got to teach a one track mind eng stuff ) ?

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With a 15 volt wall wart supply you can put 4 to 6 leds in series and
cut the current needed by a factor of 1/4 to 1/6.

click on this....only \$6 US

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It's very simple: you put a 100 ohm (brown, black, brown, gold) 1/2 watt or 1/4 watt resistor from the +5V to the lead on the LED that does not have the flat spot next to it.  The other LED lead with the flat spot goes to the negative 5V.  The white or blue LED will have a little more than 3 volts across it, and the resistor will have a little less than 2 volts across it, which will be about 18 to 20 milliamps, just about the max current for the LED.  If it is a red or orange LED, the voltage across it will be less, and the current will be more, around 30 milliamps, which is about the maximum for red LEDs.  The resistor and LED use 1/10 watt of power and will get warm.  If you put a lot of these in a confined space, they will get a lot warmer, so make sure they have good air circulation.  In all cases above, the LED will be a standard 5 mm diameter LED.  Each resistor and LED combination goes across the 5V wires, so they are all in parallel, no Joule Thief is needed, nothing else is needed. For fifty white or blue LEDs the total current is .02 times 50 or 1 amp, at 5 volts that is 5 watts.  Make sure your power supply can handle more than 1 amp, I would say at least 1.5 amps to be safe.  Get 50 LEDs and fifty 100 ohm resistors and get to work!