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too many volts to an LED Answered

I have an LED that is supposed to take about 2.8 to 3.4 volts.  A single 3v coin cell works great.  However, if I use two or three of those batteries, it gets ULTRA bright.  My question is, what harm is this doing?  Risk of burning out the light, causing heat, other bad things???  What exactly would happen over prolonged use?

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5 Replies

lemonie (author)2010-04-26

You'll "fry" them pretty quickly.

L

Kiteman (author)2010-04-26

I accidentally put 4.5V across a cluster of LEDs wired in parallel last night (guess who forgot about the need for resistors?).

Several are now dead, I don't have spares that match, and the project needs to be finished by the end of the week - that means that I will have to spend lesson-planning time at school re-soldering whole clusters of LEDs instead.

:-(

kelseymh (author)2010-04-26

Ouch!  Thank you for making this a teachable moment, Kiteman :-)

kelseymh (author)2010-04-25

Look up "LED IV curve" in Google (that is, current (I) vs. voltage (V)), and take a look at some of the plots.  The current drawn by an LED is not linear in the voltage (it's not a resistor, after all).  As you raise the voltage, the current goes up like a power law, and eventually exponentially.

That current has to flow through the rest of your circuit, heating it up.  Your batteries also have to supply that current, draining them more quickly (or damaging/overheating them).  Raise the voltage too far, and the diode will break down.

All of those consequences are dependent upon just how much voltage you're using, and the specs on your particular LED.  Now that you have seen the basics, go look up the datasheet for the specific LED you're using, and check out it's specific I-V curve.

Willard2.0 (author)2010-04-25

Running too much voltage will burn the LED out.  It is only a matter of time.

I burnt out a couple of 3V LED's by accidentally running 9V through them, they went really bright, then went really dark, then released the mysterious blue smoke and started to stink.  This all occurred within ~5seconds.