LED burnout

I've been having trouble with LEDs. I'm running 18 blue ultrabright in parallel. The specs for volts and amperage are as follows: 3.6v typ 4.5v max 20ma typ 30ma max Each LED has a 220 ohm resistor which was calculated for a 9v source with each LED at 4v, 25ma. This seems well within their range. But, in about a year and a half's time, I've had about 25% burnout. Most of the others are showing signs of intensity and spectrum degradation. Any thoughts as to the cause of this?

Super_Dave4 years ago
If it was me, I'd run 9 banks of 2 LEDs and a 90 ohm resistor for each bank.  (9v-7.2v)/.02 = 90 ohms
Goodhart6 years ago
Is your power source a batter, or is it a power supply? There is a possibility that you are getting rippleif from a PS, and that reverse voltage is lessening the life of your LEDs. Just a shot in the dark....
NachoMahma6 years ago
. Two guesses: a bad batch of LEDS or there's more current flowing than you think. Takes some measurements and make sure the volts and current are in spec. . Oh yeah! Your power source may be putting out a spike when you turn it on or off.
hexedene (author)  NachoMahma6 years ago
I have max readings of 9.58v. That keeps me in a safe zone. The current, though, don't they just draw whatever they need? Maybe it was just a bad batch. Have you any preferred sources you utilize?
. If the voltage is right, then, as you say, the current should be right. . When I need an LED, I rob it from something in the junk box. There have been several posts with recommendations for suppliers - search for LED over on the left side of the page. For the first search, I'd check all the boxes. If you get too many hits, start unchecking items.
gmoon6 years ago
If the specs are detailed, I'd look closely. Sometimes the max is for intermittent current and voltage, for instance 100 milliseconds (pulsed.)

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