How can you find the voltage and current rating of an LED? (without the convenient little slip telling you)

A while back I made a batch of sun jars that stopped working after a bit. I think it's the LEDs, but I'm not sure how to go about testing that, or finding out what to replace them with.

I used this path light - and although I could just replace the light, well thats just not as fun.

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jeff-o6 years ago
The LEDs probably didn't die, it was probably the batteries. Those solar path lights are shipped with freshly charged batteries, and if the solar panel isn't beefy enough to fully charge the battery, it slowly dies and eventually can't be charged anymore.

So, check the batteries first. Disconnect the solar panel (or just cover it up) and pop in a fresh alkaline battery. Does the LED light up?
seandogue6 years ago
For smaller <50mA LEDS, it's quite easy to determine the appropriate voltage and operating current using a 5V voltage supply, a 10K trimmer pot, and the led to be tested.. You connect one end of the trimmer to the +supply, the other end and the center tap to the LED's anode (+), and the other end of the LED, ie cathode (-) to the negative supply.

It's very important that the 10K pot be adjusted so that from the start, it will have 10K of resistance across it, so that very little current can flow..basically a quasi "open circuit"

You then start turning the gtrimpot until the LED glows the color that the LED is supposed to produce. When it starts to saturate, ie, starts to change to a slightly more red color, back the trimmer off a bit until you again find the "sweet spot. Personally, I prefer to run LEDs slightly below their rating, although there are many who swear by riding the edge. I believe in conservative engineering, because things last when you build them that way. I believe in maintaining things, rather than tossing them out. I am not part of the green revolution of rich punks who talk that talk and don't walk the walk.

Measure the voltage across the diode. Now break the connection pretty much anywhere, insert an ammeter in series and measure the operating current.

And that's the difference between professional and a white lab coat and a bought badge.
MarcinR7 seandogue11 months ago

Thanks for informative answer!

viswamtvs5 years ago
thank you
lemonie6 years ago
If the led burns out your using to much voltage or current lol.
Voltage depends a lot on the colour. Current is more of a guess.