I have a led wiring question. I’m using 12v leds 5mm 10,000 mcd and 220 ohm resistors and they seem to work fine but when I connect more leds they start to dim. So my question is, should I use a different resistor when I’m connecting more then 5 leds? Witch resistors you guys recommend? And if I can connect more then 20 leds witch resistors to use? If some one has wiring diagram please email me @ starinskiy@yahoo.com. Thanks!!!!!!!!!!!!!

 

Impossible, I call . That's one POWER HUNGRY led. You need to apply some simple arithmetic here, my man.

You need to find what the working voltage if of the LED (Vf). So let's say that we are using a single LED. Our working voltage is 13.4V, let's call our Vf 1.8. So...

13.4 - 1.8 = 12.6 V left in the line

Now, we need to consider how many milliamps (mA) are needed to actually light the LED...most run full capacity @ 20mA (Yours might be different). Now, simply divide the desired current into our voltage supply and we get the ohms-resistance needed.

12.6 / 0.020 = 680-ohms.

680ohms / 220ohms/resistor = +3 resistors to run the LED SAFELY.


Now, let's also consider if we ran 7 LEDs in series. 13.4 - (7*1.8) = -1 V. So now, we don't need a resistor.

CONCLUSION: Find out what your Vf is before you start sourcing out power supply insufficencies.

 

Yeah, just what Metal said. Also, you can wire them safely like 3-4 LED's in "series" on one resistor, before you can actually see a difference in brightness.(Or, maybe even more, depending on the resistor and LED of course). I did this with the shifter lamp under the A/C unit. Just make sure you achieve a positive and negative lead when you tap into the resistor and 12V lead. I used 3mm 5000 LED's for this setup and it's enough brightness at night.

 

and what resistors you used for 3-4 leds? thanks

 

Again, I don't know the specs for your LEDs. Find the specs and use the above equations

 

thanks!!!!!!!!!!!!!!