most 5mm leds use 20mA current...use an led wizard if you don't want to bother with the math:http://led.linear1.org/led.wizusb is 5 voltsthe voltage drop is about 3 volts (per your question)and the number of leds is ...however many you want. Because 3 only fits into 5 one time, you can't have series strands. You must drive EACH led with a resistor on each (or risk burning them out prematurely).The wizard says to put each led in series with a 100ohm resistor based on these numbers.
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That's strangehttps://www.instructables.com/answers/How-can-I-setup-5mm-leds-whiteblue-30-or-32-m/You asked exaclty the same question, and I gave you exactly the same answer.....Steve