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Scooter Blue Leds

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payguns

New Member
Hi everyone, newbie here looking for a little advice on a project my lads undertaking on his scoot.
like most lads of his age wanting to mod his bike we decided to fit a set of cold cathode neon tubes.. well that was a waste of time and money as they just blew out! as did a single which was recommended on ebay yeah right.
Now i have found a set of xmas lights that run off 4.5 volts with a , i think , 57 ohm resistor in blue with green, burgundy?, gold, gold banding soldered at switch to + pole.
question is , is it possible to run the 20 blue leds attached to the battery in series but im not sure what resistor i would need.
scoot gives out approx 12-14 volts.
hope someone can help as lad hasnt stopped pestering me lol:(
many thanks

Paul
 

crutschow

Well-Known Member
Most Helpful Member
A blue LED has a typical voltage drop of about 3V. Thus if they run off of 4.5V, the must be in parallel with a resistor in series with each bulb. (For 20mA nominal current and a 57Ω series resistor, this would indicate the voltage drop of each LED is 3.36V.)

You can only put three of them in series (with a suitable current limit resistor) for a 12-14V supply. You could put seven sets in parallel: Six sets of three in series plus one set of two in series to get 20 LEDs total.

For 20mA typical operating current you would need a ≈170 ohm resistor (3 each) in series with each string of three. You would need a ≈340 ohm resistor in series with the one string of two.
 
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