What power supply and resistor should I use for my LED lights(50)?

Hello guys,

I am having some trouble with my LED lights. I am thinking to solder about 50 LED lights (3V, 20MA, 5mm each) and install them to my keyboard. I was thinking to use my keyboard's card but seems like it does not give enough power. I have tried with one LED light bulb, it worked fine but after I solder 2 together, it seemed like it lost its power about half. So If I go over 2, it wont work. I am looking for some resistors and power supplies to fix this problem but I am not sure what volt to choose for the power supply and what resister to choose. Can some one help me please?

Thank you,

bwrussell5 years ago
THIS is a great calculator for parallel-series LED arrays.

Yes you need resistors, no matter how you arrange your LEDs.
You can get away with a power supply of 3V if you put all 50 LEDs in parallel but this takes a lot of space, a lot of resistors, and requires a full amp of current. Use this simple equation to help pick a power source: VSource >= VLED x (# of LEDs in each series). if you want 3 LEDs in each series leg then you need at least 3*3=9 V. Plug 9V into the calculator above and you will see the options. (It's best to use more voltage than required just to be safe, e.g. 9.5V or 10v instead of 9V.)

Also when designing parallel-series arrays it's helpful to use a series length divisible evenly by the total. In this case 2, 5, 10 so that you can use the same resistor for each leg.

Don't forget to check the current requirement in the "Wizard says:" section below each solution.
tkoptur1 (author) 5 years ago
Do I have to use resistors or just a parallel wiring should be ok? Can I use a computer's power supply or would it be too much?
Re-design5 years ago
Sounds like you wired them in series. It would be better if you made a separate power supply, especially since you're going to be adding so many together. You can figure out what you need with an led calculator.