Simple LED Circuit Project For Kids - Fire Hazards?

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Christa Hilda Hastie

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Hey guys! I am doing a simple project with kids to teach them about electric circuits and want to know if anybody has insight on any fire dangers with my project. Basically we are connecting 1 simple cheap LED to 2 AAA batteries with basic electrical tape....if they left the light on would it cause a fire (assuming it was laying on paper or fabric or something potentially flammable)? Any info would be helpful!
 

Current through LED can be max 20 mA (more than that your LED will be dead). V across LED will be 2.1V (red/green led). Max power will be P = VI = 2.1*20 mA = 420 mW. So, it won't burn anything but if battery + and - shorts then spark may ignite gasoline or LPG or other inflammable items.
 
You DO NOT connect a 1.8V red LED directly to a 3V battery because it will burn out soon. You connect the red LED in series with a 62 ohm resistor to limit its current to 20mA.
Maybe you arte using a "3V" white LED with cheapo weak Super Heavy Duty battery cells. But a white LED might be 2.8V or 3.5V and new name brand alkaline battery cells are powerful.
 

I hope you have dozens of LEDs on hand - the kids will never tire of seeing the bright flash of the LED, even if it only lasts a fraction of a second.

Then they can use the burned out LEDs to make jewelry, space creatures, and ..................... [You need the resistor, as others pointed out. You could 'hide' in the battery pack to make it less prone to damage and enforce the current limiting].

Why use electrical tape? Use insulated alligator clips! You want it work - not be a source of frustration and sticky fingers.

To your query, I don't see any fire hazard - unless as milan.rajik pointed out the battery is shorted - even then it would be a very small risk.

Also tell them to NEVER EVER to 'test' the LEDs with a wall outlet.
 
Uh, folks, don't forget 'throwies' connect an LED across a 3 Volt coin-cell, relying on such cells' considerable internal resistance at the working current to prevent prompt burn-out.

And, yes, degradation and/or early failure of that some-what overloaded LED is accepted given the combination is seen as expendable...

==
Fell into this topic via my own query about *when* it was noticed that LED + 3V coin-cell = Fun.trick.

I know 'throwies' (LED+coin-cell+magnet) surfaced in 2006; that's well documented. Sadly, no-one seems to remember when the 'LED+coin-cell' trick originated...
 

AAA battery cells are much larger than coin-cell battery cells so they have a much lower internal resistance so they can burn out an LED much quicker than a coin-cell.
 

"...relying on such cells' considerable internal resistance at the working current to prevent prompt burn-out."

Thank you.
 

Other than sparking their imagination, I'd assume there would be no fire risk (if you turned off the LED soon if it burnt out), but you'd probably want to use a resistor just to avoid blowing up the LEDs.
 

AG, when we down-sized after my retirement, I donated a dozen big crates of electronics books, magazines and equipment to our local tech college. As far as I know, they're still there, gathering cob-webs, waiting for their first student in too-many hundreds who'll show a flicker of curiosity beyond 'ooh, shiny !'

In this thread's context, it would be the student who looks at the "2xAA + R + LED" circuit and says, 'But my cousin Darren does it with just a coin cell and LED; how so ?'

It may be a 'flash in the pan', it may lead to domes on Mars.
 

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