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We are making paper circuits at school. The students will be making a circuit using double-sided copper tape, an LED (in various colors, R/Y 2.0-2.2 volts, B/G/W 3.0-3.2 volts) and a power source.

Which battery should we use? Maybe a CR2032 or CR2025?

Velvel
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Allison
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  • How long do you want the circuits to stay continuously illuminated? Lithium chemistries are all roughly 3.6 V, so it's just a question of capacity, which ultimately only will manifest in cell size and circuit run time. – JYelton Aug 18 '23 at 16:25
  • They will illuminate when the students complete the circuit by folding over a section of their paper craft (with copper tape on it ) and touching the battery. – Allison Aug 18 '23 at 16:45
  • In other words, the LED only stays on while the student maintains the connection. Fair enough. Imagine the student does this for a few minutes every day. Hypothetically, the difference would be that the larger battery would enable this to work for N days, while the smaller battery would enable it for 72% of N days. – JYelton Aug 18 '23 at 17:12
  • You might want to test the LEDs before the class to check for any faulty ones, to avoid disappointment. I think that the leads should fit across the two flat faces of a CR2032 cell for a quick check. – Andrew Morton Aug 18 '23 at 17:12
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    The CR2032 IS NOT a "3.6V" rechargeable Lithium battery. It is about 3V when new and when it has a very low load current. – Audioguru Aug 18 '23 at 19:58
  • @Audioguru I was thinking of ER (thionyl chloride) chemistries (that I work with often) instead of CR (manganese dioxide). Both are primary (non-rechargeable) but the former is 3.6 V while the latter is 3 V. Thanks for the clarification/reminder. – JYelton Aug 19 '23 at 15:30
  • I recommend that you don't give 3v button cells to students. if any of the students has an infant sibling there is a serious risk of fatal burns, – Jasen Слава Україні Aug 20 '23 at 02:10

1 Answers1

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Small lithium coin cells have a relatively high internal resistance and thus may serve as the current limitation to protect LEDs from over-current (more on this here). The only difference between 2032 and 2025 cells is size and capacity. (The first two digits, 20, refers to the diameter. The last two digits, 32 and 25, refer to the cylinder length or thickness in this case. The -25 is 2.5 mm thick, while the -32 is 3.2 mm thick.)

If your project has any dimensional requirements (e.g. battery must fit into some enclosure) then your choice will largely be dictated by that. Otherwise, the 2032 will have greater capacity and run the LED for a longer period of time. The datasheets I linked above list the following capacities:

  • 2032: 235 mAh
  • 2025: 170 mAh

If the run time isn't important, go with whatever cell you can get more affordably (I'm assuming you are a teacher and your budget is limited.)

JYelton
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  • Thank you! And yes, I'm a librarian that likes to throw in some makerspace projects that relate to our read alouds. I appreciate the help. – Allison Aug 18 '23 at 17:12