LED Wiring help for a moron?

Birdie

Master Member
RPF PREMIUM MEMBER
Okay, I'm trying to wire up a simple 5 led chain for a PKD custom. I put the circuit to gether and apply power. Nothing. Check all the polarities, can't find a fault.

So I unsoldered everything, tested all the bulbs and they are fine. It seems I just can't get more than two bulbs to light at a time, like so:

Two bulbs


Yay!

Single third bulb


Yay!

All three


Zippo. Boo!

I've tried substituting different bulbs, same result. As soon as I try adding a third bulb, nothing. What the hell am I doing wrong, this is driving me nutso :confused??
 

ReproMan

Well-Known Member
my guess not enough power from supply for 3 leds

Connecting LEDs in series
LEDs in series If you wish to have several LEDs on at the same time it may be possible to connect them in series. This prolongs battery life by lighting several LEDs with the same current as just one LED.

All the LEDs connected in series pass the same current so it is best if they are all the same type. The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor. To work out a value for the resistor you must add up all the LED voltages and use this for VL.

Example calculations:
A red, a yellow and a green LED in series need a supply voltage of at least 3 × 2V + 2V = 8V, so a 9V battery would be ideal.
VL = 2V + 2V + 2V = 6V (the three LED voltages added up).
If the supply voltage VS is 9V and the current I must be 15mA = 0.015A,
Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 / 0.015 = 200ohm,
so choose R = 220ohm (the nearest standard value which is greater).
 

Birdie

Master Member
RPF PREMIUM MEMBER
Good page, but just seems to be telling me I'm doing it right....very weird :confused


Man I feel your pain! Luckily I just needed 2 LEDs in parallel for the snub I got
from Goldberg Arms

I looked up some simple diagrams and found this:
Redirect Notice

Might help some! You better post some pics when you're done!!
 

Birdie

Master Member
RPF PREMIUM MEMBER
Yup, seems to be a power issue. Just hooked up a new 9v battery and it seems to be doing the job :)

Guess I'm doomed to suck a electronics :$


my guess not enough power from supply for 3 leds

Connecting LEDs in series
LEDs in series If you wish to have several LEDs on at the same time it may be possible to connect them in series. This prolongs battery life by lighting several LEDs with the same current as just one LED.

All the LEDs connected in series pass the same current so it is best if they are all the same type. The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor. To work out a value for the resistor you must add up all the LED voltages and use this for VL.

Example calculations:
A red, a yellow and a green LED in series need a supply voltage of at least 3 × 2V + 2V = 8V, so a 9V battery would be ideal.
VL = 2V + 2V + 2V = 6V (the three LED voltages added up).
If the supply voltage VS is 9V and the current I must be 15mA = 0.015A,
Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 / 0.015 = 200ohm,
so choose R = 220ohm (the nearest standard value which is greater).
 

ReproMan

Well-Known Member
im not too great with electronics either. i'd rather re-purpose l.e.d. circuits out of crappy toys to put in props lol, but im learning so i can try some of the sci-fi rifles
 
Check the specs on the forward voltage for your LED's.....(ie. voltage drop across LED's required to turn it on) Usually about 2 volts per LED.

- If wired in series, the current across LEDs is same as source but voltage is divided.
- If wired in parallel, the voltage across LEDs is same as source but current is divided.
 
Top