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Discussion Starter #1


I need to know what voltage the resistor from my diagram needs to be in order for all 10 of my LED's to get an even 5 volts of power. How do I figure this out? (been awhile since Physics...)

Rep for those who help me out!!! Thanks [thumb]
 

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Any resistor will do. All it is doing is keeping the current from the battery from being too high and draining the battery. Choose a resistor with a fairly high value.
The resistor will drop whatever voltage the LEDs dont drop. Confused yet? lol


I would say a 5K or 10K ohm resistor would be good.
 

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i am running 3 LED's off a 680ohm resistor
 

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Do you have the specs for the LED's? Nominal voltage and current? Typically, a 5mm LED will take around 60ma and 3 volts. Yours are 5 volt? Also, if your serious about an "even 5 volts", then you need a voltage regulator (not hard to do at all. RS has them in fixed output voltage ranges). You also need to calculate the wattage. Power (watts) is Voltage time current. So if ALL of your LED use 50ma each, and you have 10 of them. Then .050 x 10 = .5 amps, x 5 volts = 2.5 watts. Typical resistors are .25 watts.
(Note: Blue LED generally take more power than yellow or green LED. Just FYI)
(Nuther Note: Just FYI: depending in what your doing. be aware that you also want to consider the "diffusion" angle of the LED. As above. Blue LED have poor diffusion).
 

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where are you putting these?
 

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Discussion Starter #7
I'm actually all set guys. I used a 5V voltage regulator. This way I always get 5V no matter what. The resistor just resists currents at a ratio, and since the battery is not always exactly 12V, I wont have brighter/dimmer lights based on my battery becuase the regulator allows only a consistent 5V through. It's perfect, and I reccomend it to anyone thinking of doing this...

They went in heater vents/door panels though
 
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