These LEDs use to work inside my project. Then I left the project alone for about 2 years. When I came back to it the LEDs are not working, sort of. When you look at my attachment it shows two LEDs in series. The project has 5 pairs of these LEDs. Each pair use to work fine. Now each 1 of the 2 LEDs works fine by itself but together NO. What is going on?
Any current limiting resistor ?
What's the voltage drop for your LED ?
The voltage drop is 4 volts with out the limiting resister. And 3 volts with the limiting resister. There is only .2 volts left after the first LED. No wonder the second LED is not lighting. But it use to work fine. What do you think happened as it was sitting in the closet for 2 years?
you usually don't use leds without current limiting resistor. The Led will draw all the current it can from your power source and kill itself : )
Did not know that. I thought it just got too bright. I'm going to see if a more restrictive resistor will do the trick. Thanks for your help.
read about leds, voltage drop etc...
here is a google hit about that
Look up the VF for each color, then add them together and subtract that from your source voltage. Then you can use Ohm's law to calculate the resistor value, start with maybe 5mA and then adjust to suit. Expect different colors to have a different VF.
I think after two years you forgot how they actually worked. They may have a current limiting resistor built in.