Instructables

Help!!!

ok my project involves 4 LED's in parallel connected to 3 AAA batteries in series. Individual LED's keep stuttering and then finally going out after a few minutes. Is this a problem with the power source? Or are my LED's just bad?

Artemis6 years ago
well, it sound like you're running too much voltage through the LEDs. A simple solution is to put an oppropriate resistor between the first LED and positive end of your power supply, although it is recomended that you put one in front of evry LED. Remember, if your LEDs are in parallel, then every one of them is pulling 4.5 volts. A simple way of figuring out the correct resistor is by looking at a website that will do it for you, or using the following equation:

R = (V1-V2) / I
or
Resistance(ohms) = (voltage of power suply - voltage drop of a single LED) / target ma
*note: this is for parallel only. In a series you would add the voltage drop of all LEDs for the value of V2

I hope this helps and if I am at all wrong, anybody can feel free to correct me. My understanding of these things is basic at best. Good luck . . . maybe I'll enter something :)
Artemis Artemis6 years ago
sorry 'bout t3h spelling.
Lftndbt6 years ago
Quote:~ "LED's in parallel connected to 3 AAA batteries"
3 x1.5vAAA = 4.5v

"I think they have about 3.2volts rating"

Do they burn out... as in don't work anymore?
Check it they don't get really hot and burn out....
If so.. dido... resistors...
westfw6 years ago
If you have no current limiting resistors, you're probably burning them out, especially if they're not UV, white or blue... (those have a voltage drop close enough to the 4.5V supply you have that current MIGHT stay low enough not to fry them...)
pmac93 (author)  westfw6 years ago
The LED's are blue, I think they have about 3.2 volts rating. I have a blue LED flashlight that has 8 LED's in parallel connected to 3 AAA's so I thought it would work.
westfw pmac936 years ago
Yes, the sort of arrangement you have is very common in cheap LED flashlights; I'm not sure how they get away with it (one possibility: buying huge numbers of LEDs at a time means that the LEDs in any one flashlight are closely matched in electrical parameters, while if you grab several LEDs from different batches with slightly different Vf parameters, one will grab more than its share of the total current (and more than it can take) till it burns out. Then the next....)
schorhr6 years ago
Ad resistors ;)
schorhr6 years ago
pmac93 (author)  schorhr6 years ago
nope no resistors, and they're 4 blue LED's in parallel.