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Since I haven't dealt with voltages/current/etc since highschool, I'm not super confident in my abilities to not blow up a bunch of LEDs - I read a few guides, but would appreciate if someone could confirm I'm on the right track!

I'm using two 9v batteries adding up to 18v to power the system, and running 10 LEDs in 5 groups (2 2.2v, and 3 3.2v). The total voltage adds up to 14v, so my logic follows that if I use Ohm's Law on the two groups running 2.2v at 20mA, I need a 100 Ohm resistor on both to eat up the remaining 4v (2/0.02 = 100).

My questionable diagram

Would I be correct in my logic, or is there something I'm missing? Any guidance would be very appreciated!

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    \$\begingroup\$ You put 18 VDC on two LED and a 100 Ohm Resistor.... That don't looks good \$\endgroup\$
    – Mike
    May 27, 2021 at 10:07
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    \$\begingroup\$ And you put 18VDC on two LED without a resistor.....really bad \$\endgroup\$
    – Mike
    May 27, 2021 at 10:08
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    \$\begingroup\$ "That don't looks good" and "really bad" doesn't help me get any closer to an answer... \$\endgroup\$
    – idkartist
    May 27, 2021 at 10:20
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    \$\begingroup\$ i didn't know the exact current that your LEDs needed because you did't gave us the parameter but, check this link and i think it works for you : drive.google.com/file/d/1A4EdAMraDbu5bhKNqz6VVpqliOIbs32v/… \$\endgroup\$
    – Curious guy
    May 27, 2021 at 10:59
  • \$\begingroup\$ Ahhh! That makes far more sense - I think I got a grasp on it now, thank you so much! I really appreciate the effort you went through to illustrate it for me :) \$\endgroup\$
    – idkartist
    May 27, 2021 at 11:11

1 Answer 1

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No, that is not correct.

That will apply 18V to the all the strings.

9.6V strings of LEDs get 18V, and they get damaged.

It will also apply 18V to the 4.4V string with 100 ohm resistors, so 13.6 V is over the resistor and 136 mA flows in the resistors and LEDs. The LEDs will damage if they don't handle 136mA. The resistors will damage if they can't handle the 1.85 watts power dissipation.

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  • \$\begingroup\$ Dang, I must've misinterpreted the guides I was reading... I appreciate the confirmation nevertheless, you've saved me quite the headache! If I think I understand your reply, would something like this be closer to working? i.imgur.com/NobFNrD.png \$\endgroup\$
    – idkartist
    May 27, 2021 at 10:40

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