78Views10Replies

# Resistor Value for LED series? Answered

I am new to electronics, just started it as a hobby, and tried my hands to make a LED Series. As I am not aware of the exact calculations to figure out the resistor value, I am facing problems - resistor is getting burnt. I am just seeing a led series bought from the market and trying to make another one based on its circuit & design. The overall scheme & design of the circuit was:

- I made a series of total 44 white led lights.
- Added a bridge rectifier first (4 diodes joined in a systematic way),
- then came three led's with 1K Ohms resistors each
- then followed 38 plain led's,
- finally three leds again with 1K resistors each.

The last three resistors got burnt after 10 odd minutes. Obviously the resistor value is not right. What should be the general thumb rule to figure it out.

I wish to make few smaller series of 12, 24 & 36 LED's, how many resistors do I add in each?

Will be thankful for some guidance.

Tags:

## Discussions

As your a beginner I will expand a little - You need to use Ohms law (best look it up.

Voltage = Current x resistance Often printed as V=IR - If you know 2 values you can calculate the other one.

Your LED currents in series will add up so lets assume 10mA each - 12 x 10 Ma = 120 Ma total current.

If your supply is 10 volts. Each LED needs say 2 volts so you resistor will need to drop 10-2=8 volts and pass 120 Ma.

So from Ohms law : R=V/I

R=8/0.120 because a milli amp is 1/1000th of an amp.

= 66.6 Ohms In reality I would go for the next higher standard value - This will give slightly lower current but that is safer.