Calculating Resistor Values for LEDs in Series




Introduction: Calculating Resistor Values for LEDs in Series

About: It's not important who I am or what I know. What is important is what I can teach you.

R = ( VS - ( VL x n )) / I

The calculation of how a resistor reduces Voltage (pressure), is very important in electronics. The value of the correct Resistor for LEDs in Series is the Supply Voltage (pressure) minus the total pressure consumed by all off the LEDs (Voltage Drop Across a Single LED times by the total Number of LEDs), that answer is then divided by the LED Current (electron flow) required by the circuit.

R = ( VS - ( VL x n )) / I

Calculated Limiting ResistorOhms

Resistors do not come in every value of ohms, the answer you get from the formula may not be available in real life. You will need to select the next nearest higher value resistor based on the number calculated above (Real Resistor Values).

Nearest Higher Rated Limiting Resistor

Supply Voltage ( VS )
This is the Voltage of the power supply. Volts

Voltage Drop Across a Single LED - Load ( VL)
For most low power LEDs this is 1.7 Volts. Volts

Desired LED Current ( I )
For most low power LEDs this is 20mA. Amps
(Quantities and Units)

Number of LEDs( n )
How many leds connected?

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    7 years ago on Introduction


    i have had never made electronics, although i am very enthusiast about making something.

    i have some ideas in my mind all the time, but i have no equipment except a soldering gun, (that's it) my financial situation is bad because every thing is so expensive and i make the minimum wage in san francisco, i tried to get into the workshop "make" but results impossible because the money issue.

    What i want is to put in a hose a lot of led's multicolor very bright led's, it is something i want to put along the frame of my bicycle, may be about 100 or more led's.

    what do i need and where can i buy affordable resistors and the leds, and batteries and cases, and how do i start working on them.

    may be it is sort of silly to ask for but i want to start in electronics since long time, i did lost my interest many times due to depression.

    any good advice be welcome.


    i apologize for my grammar.


    Reply 2 years ago

    Even me brother same as your condition...

    C P
    C P

    4 years ago

    Awesome! Thank you for this review!