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About a week ago, I have been soldering exactly 29 LEDs to a PCB in an effort to replace my old, custom taillight bulb that came with my motorbike since I bought it. I have successfully managed to solder the LEDs onto the board and I already did the wiring. Since I bought my LEDs on an electronic market, and they did not come in a package, I have no idea exactly how much voltage they need nor how much AMPS they require. Since then I have been trying to hook them up to multiple voltages including 3v, 6v 12v(which will be the voltage used by my bike.) I have also been researching about my issue and believe that my problem has to do with some form of resistor I will be needing.

I look forward for a good solution!

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  • \$\begingroup\$ The LEDs are just regular ones if you ask me, but aren't as log as usual ones, they are flatter. \$\endgroup\$ – David Feb 11 '13 at 5:53
  • \$\begingroup\$ The color is red, I couldn't post a photo, as I am only a guest \$\endgroup\$ – David Feb 11 '13 at 5:53
  • \$\begingroup\$ Please post the photo on any public photo site, and add the link to your question. Also, a diagram or even hand-drawn sketch of how you have the LEDs wired up, please. \$\endgroup\$ – Anindo Ghosh Feb 11 '13 at 5:54
  • \$\begingroup\$ i.stack.imgur.com/aKZQ8.jpg \$\endgroup\$ – David Feb 11 '13 at 6:08
  • \$\begingroup\$ i.stack.imgur.com/tvS9S.jpg \$\endgroup\$ – David Feb 11 '13 at 6:10
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To wire ~30 LEDs at 12V (bike voltage) use the following wiring diagram:

enter image description here

You will need resistors to limit the current. Using the resistor value of 100 ohm will limit the current to ~15mA (chosen arbitrarily as you don't know how much current your LEDs will need) per LED (@ 5 LEDs in series).

The brightness of LED is dependent on the current flowing through it therefore you would have to experiment with the amount of current as you don't have the DATA on the LEDs. To increase the amount of current through a LED you would have to decrease the series resistor.

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  • \$\begingroup\$ Thank you for the detailed answer, since I have already soldered everything into place, would it be possible to only use a single 100ohm resistor attached to the wire coming out of the wire bundle? \$\endgroup\$ – David Feb 11 '13 at 6:20
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    \$\begingroup\$ @David - no. You would need a different value, higher power resistor, and it's a really bad idea, as you can get uneven current-sharing between the resistors. \$\endgroup\$ – Connor Wolf Feb 11 '13 at 6:24
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    \$\begingroup\$ @David, that normally isn't a good idea because of manufacturing differences between devices. Just as a side-note if you do have 30 standard LEDs you might be disappointed with the light output, it might not be bright enough to be legal / safe. \$\endgroup\$ – PeterJ Feb 11 '13 at 6:25
  • \$\begingroup\$ @David Post your connection diagram. \$\endgroup\$ – Chetan Bhargava Feb 11 '13 at 6:26
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    \$\begingroup\$ @David For your future projects, get parts for which you can get a datasheet. In other words, don't get P.O.U.P. (parts of unknown pedigree). If it doesn't have a datasheet, then don't get it. LEDs are not all created equal. They have different different max current, different voltage drop, different light output. You would know what these parameters are from the datasheet. Then you can get best results. \$\endgroup\$ – Nick Alexeev Feb 11 '13 at 6:30

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