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What type of battery or resistor should i use to light up 5mm LED ?

What type of battery or resistor should i use to light up 5mm LED ?

Old 02-14-2012, 06:51 AM
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Default What type of battery or resistor should i use to light up 5mm LED ?

Hi guys , may i know what type of battery should i use to power up LED for my truck ? I'm using those 5mm super bright type of LED . Or what value resistor should i use to lower the current ? Sorry i had to ask that cos i suck in my analogue electronics in school . I tried using CR2016 but it seem to lose its power pretty fast . I'm planning to power a total of 8 super bright LED front and back .

I just had a small explosion ( sounds like a small firecracker going off , if you want to know the sound ) from one of the LED when i tried to use my 3s 35c 850mah lipo battery to power it . And the LED was blown to bits but luckily i was unscathed .

I know there are lighting kit for cars available but i want to DIY my own lighting system .
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Old 02-14-2012, 11:58 AM
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The Ultrabright 5mm LEDs are typically 3v rated. If you really think it is not as bright as claimed, then you will have to find out which rating they are. If you are unsure, you may use a variable voltage AC-DC adaptor and adjust the voltage till just about the correct brightness that you believe the LEDs should emit and note down the voltage you are at.

For a 3V Ultra bright LED, it should be rated between 30 - 100ma. I calculate all of mine as 50ma. To resist a 12v 3S lipo to nicely power a 3V 50ma LED, you will need a 1W 180ohms resistor per LED.

Get your calculations right, have fun and be safe! Brave of you to had attempted to power a 5mm LED with a 3S lipo! I had a mini flash bang when I used 5V.
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Old 02-15-2012, 07:42 AM
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Thanks bro , great help you gave . Its more of ignorant me to attempt that haha . But then again if i never did that , i would never have known that LED CAN ACTUALLY EXPLODE lol . Definitely a new lesson for me to take note of .

Its not that its not bright , just silly me trying something stupid lol .
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Old 02-15-2012, 08:37 AM
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You might want to use a 250ohm resistor for a 12v source instead if you're looking at 50mA.
Cos 12V/0.050A = 240 ohms

If you're connecting to 3s lipo which 12.6V when fully charged then a 250 ohm resistor is safer if the current is 50 mA.

From what I've read on LEDs, some are rated at 20 mA max current.

Btw, R = V/I ... (to clarify, V here is not supply Voltage but potential difference across the resistor... must also clarify that I'm assuming that the resistance of the LED is very small, and hence the potential difference across the LED to be practically zero - this way, you have a worst case scenario calculation - it will probably not lead to max brightness, but it is highly unlikely that your LED will explode)

You can basically ignore the resistance of the LED when you're determining what resistor to use, you should also take note that LEDs do not have constant resistance ... their resistance drops when the voltage increases.

So, the purpose of the resistor is to limit the current so that the LED doesn't blow up.

Last edited by Cirrc; 02-15-2012 at 11:05 PM. Reason: Some typos and adding clarity.
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Old 02-15-2012, 11:25 AM
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The formula for LED's resistor calculation is a little different.

R = (Vcc-Vf)/If

Vcc = Supply Voltage
Vf = Voltage drop
If = Desired current

At 12.6v fully charged, you will be looking at 200 - 220ohms for 3v 50ma UltraBright LEDs. 20ma rated LEDs are not considered in the UltraBright catagory, they are typical LED ratings, 30ma is beginning to be the new standards now.

I recommend 180ohms mainly because the LED will spend most of it's time hovering closer to 12v on a 3S setup R/C situation, the LED will strain during the 12.6 period but it will sustain brilliant brightness through out the entire 3S lipo's discharge period when used with a 180ohms resistor. 180ohms is the sweet spot that I had derived from fiddling around with LEDs for R/C applications.
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Old 02-15-2012, 11:47 AM
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Do note that different colors of LED may have different voltage rating.
Heres a table for 5mm LEDs that I use and had been proven true for most of my experiments.
  • Infrared (930nm) = 1.5v
  • Red (635nm) = 2v
  • Amber (615nm) = 2.1v
  • Green (570nm) = 2.2v
  • Blue (480nm) = 3.3v
  • UltraViolet (400nm) = 3.4v
  • White 5000-10000k = >3.3v
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Old 02-16-2012, 05:10 AM
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Noted , this is what i like abt DIY , you get to learn lots of new stuff while trying to built it . And the satisfaction you get after everything is done and working .
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