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Hey guys a little info needed and will be much appreciated. Knowing bugger all about this rite now, i bought 10, 5mm diffused white leds, 5v. Ive got my thin wiring and was about to set them up but what sort of power source should i be using for these?? Also would these be ok to put in the likes of a pit garage to give sufficent lighting IE life wise and to keep good power? Thanks
 

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No such thing as a 5V LED. You need to run a resistor in series with the LED otherwise you will kill them. Im assuming that you want to run on 12V. About 15mA (0.015 A) current is about OK. The white LEDs drop 3V.

So 12V - 3V = 9V

Resistor value you need is R = V / I

R = 9V / 0.015 = 600 ohms. Use either 560 or 620 which are the values closest to 600.

You could run 2 or maybe even 3 in series but then the resistor value would change.

If you run 2 in series
12 - 3 -3 = 6V

R = 6 / 0.015 = 400 ohms use 420 ohms

If you run 3 in series

12 -3 -3 -3 = 3V

R = 3 / 0.015 = 200 use 220 ohms

And before you ask can I run 4 in series and then I dont need a resistor, no you cant do it safely!!!! LEDs are diode so connect the long leg to the positive voltage and the short leg to ground. If in series you go long to +ve then short to the long leg of the next LED etc. Daisy change everything together. Hope that helps.

rick1776
 

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Hi,
Are the LEDS you have pre-wired with the resistors or are they just bare LEDs? Pre-wired ones will have a black wire and a red(or other colour except black) soldered to the legs of the LED, These joins will be covered in heat shrink one of the joins will have a 5mm(ish) long blob in it, that's the resistor. If they are bare LEDS they will have no wired just 2 shiny stiff legs one longer than the other, these will have to have the resistors fitted as above. Note not all pre wired LEDS have resistors so look carefully for the blob.
 

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Rich Dumas
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The LEDs that I use operate at 3.5volts and 30 milliamps (0.03 amps). Here is an online calculator for sizing the dropping resistor: http://ledcalc.com/
If four of these are wired in series they can be run directly from a 12 volt power supply without using a dropping resistor.
 

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Discussion Starter · #5 ·
Hwy guys, first of thanks for the excellent info! Secondly i must have got the led V wrong, they are just plain unwired leds, with one leg longer than the other. Havent done anything like this before other than some simple school electrics so im a little out of depth as easy as it will be to do and understand. Am i ok in doing the likes of this for the pit garages? Or should i be looking at getting some different ones or doing it differently?? Basically id like to end up with a well lit pitlane.
 

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Circuit Owner
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The LEDs should be OK for pit lane garages.

I would assume the LED voltage drop is 3v and it needs 15-20 milliamps of current. So use Rick 1776's calculations.

I would try the circuit out first before committing to the installation.

The LEDs could be too dim or too bright or they could throw too narrow a beam or too wide. It would be a shame to find out after you fix them in place!

LEDs are dirt cheap on ebay and many are supplied with the correct resistors for 12v. The Superbright ones are BRIGHT - I used a pair on my Taurus NASCAR (the one I use as my Avatar) and they are 3 or 4 time as bright as standard Scalextric LED headlights and they throw an awesome beam of light that looks really authentic in the dark - they actually light up the track and armco whereas the Scalextric standard lights simply mark the position of the car.

Superbrights are probably overkill for pitlane garages but are probably perfect for track lighting if you have plans to install streetlights.

Be a bit careful with placement as bright LEDs can shine through plastic. When I installed the LEDs in my NASCAR I painted the inside of the body around the LEDs matt black so there is no light leakage through the body. You may need to do the same for your buildings.
 

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Rich Dumas
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LEDs are available with different viewing angles, 15 to 45 degrees are commonly available. For track lighting 45 degrees might be best. The intensity of the light is often measured in mcd, my HO track is lit with 44 45 degree 6000mcd LEDs. The longer of the two legs is connected to positive. Different colors operate at different voltages, red LEDs usually run at 2 volts, white LEDs run at 3 to 3.5 volts. It is better to know what the specs are for the LEDs that you want to use. If the voltage is just a volt too high the LEDs will burn out at once. If the voltage is a half volt too high their life will be greatly reduced. Be sure to measure the output of whatever power supply that you plan to use. I bought a "12 volt" power supply that actually put out 13.8 volts, if I had not taken that into account my LEDs would have gotten cooked.

 
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