Simple LED Circuit Project For Kids - Fire Hazards?

[Christa Hilda Hastie]

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!

 

[milan.rajik]

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.

 

[Audioguru]

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.

 

[kam1787]

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.

 

[Christa Hilda Hastie]

Thank you everybody! You have been most helpful! Happy Friday!

 

[Nik_2213]

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...

 

[Audioguru]

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.

 

[Nik_2213]

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

Thank you.

 

[Audioguru]

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

Thank you.

Then will you use little coin cell batteries instead of much more powerful AAA cells?

 

[Resistanceisfutile]

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.

 

[Nik_2213]

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.