what kind of resistor to use?

Question

So I am planning on getting about 20 small colored led lights on a circuit with a 9 volt battery to power it. I know I need a resistor or else I will blow out the bulbs. The problem is I have not a cluse what kind and I know little about electric terminology. I know very basic parallel circuits and that is what im using. What type of resistor would I use or should I just ask the guy at radio shack.

theradioham · Answer

Would not recommend a 9V battery, they are generally far more expensive for their capacity, compared to a battery box and AA cells.

If running on 9V, you would make them into series strings, two of the higher voltage drop blues, and 3 of the lower voltage drop red, then you would calculated the resistor for each string.

If you attempt to use LEDs in parallel, unless they are perfectly balanced, one, or one string, will have a lower voltage and steal more of the current, burning bright or burning out, while others are dim.

? · Answer

hello

every color has a forward voltage....for example red 1.8 volts and blue 3.3 volts for 20 mA current....so you use a series resistor to limit current....voltage across resistor is  R = (9 - Vf ) / 0.020
for red R = 360...use 390 ohms standard...for blue R =285...use 270 ohms standard... both are 1 /4 watts resistor...good luck

Trending News

what kind of resistor to use?

2 Answers