LED 'how to' wire, resistors.

ok iv been swamped with question on what is the correct resistor for a led (on different forums so i thought is shair the info)

so today iv drawn up a few circuits to show how to measure the voltage drop across the led and the difference the power supply makes

a car supply can vairy from 11v to 13.5v so you have to work out the maths on the maximum values other wise things go pop



here is the first drawing

this is set up with a 13.5v supply 3v drop on each led and correct rsistor for 15ma supply






ok if the voltage drops to 11v then the values change as bellow note the current drop so the leds will dim if standard type








ok here is the same circuit with 1.6 volt drop accross the led and a correct reistor







so now if the voltage drops to 11v here are the new values






as you can see from the above circuit the current does not fall to much thus brightness is less effected



so by buying good quality leds ie mega bright the vf is lower than the standard type so produced a better light source and less vairiation in power



now if you say use 12v to set your led the 2 circuits bellow show at 13.5v (car alternator chaging ) you are above the max current of the led so its life is shortend and will eventualy fail

or if you dont know the volage forward drop then tha same applies








and for the peeps who want a dimmer here is a basic circuit

I have not got a clue what any of it means (I expect it is the Chav guide to hot wiring a car) but it looks very comprehensive Mark

well john next time your over this way ill show you how to do leds ect

Thank you Mark that will be fab

Nice job Mark.
Thanks

Nice guide Mark. Added to the 'how to' guides section. Thanks for your efforts.