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My goal: I'd like to somehow make a nerf dart light up for easy retrieval at night (and to look cool, lets be honest). Putting a cell battery, a switch and an LED in them is a lot of weight and a lot of batteries to buy and switch out. Is it possible to use something like a capacitor to store a very short term charge, and power an LED for something like 1 minute? I'm not looking for long term power... give the dart a charge, and the LED runs for about a minute. Just long enough to go hunt them down.

And yes I know there are lots of other options - glow in the dark darts, UV lights, etc. Looking specifically to make them glow with an LED if possible.

InfernusDoleo
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  • You can get really tiny batteries, if thy are too big for you, then I am afraid there is not much more available, what is your weight constraint then? 0.1g? – PlasmaHH Feb 16 '17 at 15:46
  • Get tiny batteries, and create a simple LED circuit with a resistor and a switch to turn it off when you need. Battery size will be crucial to your project. – 12Lappie Feb 16 '17 at 15:53
  • @12Lappie: with an appropriate high impedance coin cell you can even leave out the resistor. – PlasmaHH Feb 16 '17 at 15:59

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Adapting How long would a 150 Farad Capacitor light up an LED (answer: about an hour), we would get that a 2.5F capacitor would light an LED for a minute. They exist, but are still pretty bulky.

I'd just stick with an appropriately tiny coin cell. If you want to overdo it you could have a Li-ion which will last for hours, but they're a bit fragile to put in darts.

Community
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pjc50
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  • Incendiary nerfs! :D – Wesley Lee Feb 16 '17 at 16:11
  • If I could find it, I'd link the history of WW2 proximity anti-aircraft shells, which managed to fit a valve-based radar set and its battery into something that could be fired out of a cannon. It was a "wet" cell with some of the electrolyte in a glass vessel, so firing it also turned it on and the battery didn't run down in storage. – pjc50 Feb 16 '17 at 16:50
  • So basically the capacitor would need to be so large it becomes not worth the effort? Was hoping to be able to have something tiny that could get a charge before it leaves the barrel then just run briefly. Looks like tiny button cells is my only option. The switch part will really screw up the project though. Cant exactly just switch them on before firing (the nerf gun has a magazine with 18 darts in it). Thanks for the advice, looks like this is a no-go unless I can come up with something pretty innovative. – InfernusDoleo Feb 16 '17 at 17:49
  • Microswitch or contacts held closed by the position in the magazine? Could probably achieve something acceleration-triggered but it's hard to miniturise. – pjc50 Feb 16 '17 at 20:09
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The only possibility would be a MN27 but at 7 grams, not likely. aka 8LR732, A27, A27BP, G27A, L828

At 0.31" in diameter it's close to the right size. I do not know the diameter of a nerf dart.

MN27 is only 1.1" length

Misunderstood
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