Coin battery experiment works with multimeter, but not light bulb. Why?

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onlinefunner
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Coin battery experiment works with multimeter, but not light bulb. Why?

Post by onlinefunner »

Built a coin battery with about 10-20 pennies and nickels.
Hooked up a multimeter and was generating around 1.5V
Then hooked up to a tiny incandescent light bulb with a couple wires, but the light did not turn on. Why not?

So, obviously I tested each component:
  • Tried using different light bulbs and leds to make sure the bulb was not the problem.
    The same bulbs did however worked fine with a single AA battery of 1.5V, so the bulb was not the problem.
    Made sure multimeter was reading volts, mot millivolts.
    Tried adding a few extra coins for extra voltage.
    It was not a metal contact issue. I used the same two wires and connected to a battery, then coin battery, pushing very hard even, but still only worked with regular battery.
Experiment: https://www.sciencebuddies.org/science- ... from-coins
bfinio
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Re: Coin battery experiment works with multimeter, but not light bulb. Why?

Post by bfinio »

Hi,

To clarify - you also tried this with LEDs (like these: https://www.sparkfun.com/products/12062) and not just an incandescent bulb? Incandescent bulbs require much more current than LEDs. Even though the voltage of your coin battery is 1.5V, which is about the same as a AA, AA batteries can provide much more current. So, I would not expect this project to work at all with incandescent bulbs. I know from our internal testing that it does work with LEDs. Unlike incandescent bulbs, LEDs have polarity, and will not light up if you connect them backwards. So if you tried with an LED and it did not work, did you try flipping the LED around?

Thanks,

Ben
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Re: Coin battery experiment works with multimeter, but not light bulb. Why?

Post by rmarz »

onlinefunner - In addition to Ben's comments, the threshold forward voltage, even for a low current LED, is more in the range of 2.5 volts, so it would only light if two or more coin cells were connected in series to increase the voltage. The current produced by a small coin battery is likely in the low milliamp range, so it might only be visible in a dark area.

Rick Marz
onlinefunner
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Re: Coin battery experiment works with multimeter, but not light bulb. Why?

Post by onlinefunner »

Thanks! Logical answer.
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