Got to solder in a large quantity of LED's and they come with a pack of resistors, so I can feed them off a 12v supply. My question is can I just use the 1 resistor on the main feed wire or do I have to use 1 resistor per LED? Will it effect brighness?

 

Cheers

 

Vijay

OllieZX is king of the LED's.

 

The one's in my dash have individual resistors fitted. HTH.

Got to solder in a large quantity of LED's and they come with a pack of resistors, so I can feed them off a 12v supply. My question is can I just use the 1 resistor on the main feed wire or do I have to use 1 resistor per LED? Will it effect brighness?

 

Cheers

 

Vijay

You must use one resistor per led or you will burn them out.

If you wire them in a chain you can use just one (depends on how many you wire together) but if you wire them parallel you will need one on each.

damn, was hoping to solder them into a stripped pcb, gonna be a bit messy with 50 resistors :(

Thinking about it, you could probably use one if you wired them in parallel, but it would have to be a much higher wattage rating. At least I think that would work ....

deffo gonna be in parallel

Well if the standard resistor is 1/8 Watt and you are going to run 8-10 LEDs off it, then you should replace it with a 1 Watt version.

http://led.linear1.org/led.wiz

 

http://www.theledlight.com/ledcircuits.html

you also need a different resister

 

say you have one 2v led and a 12v car

led likes about 20ma

so you are looking at 10v being dropped across the resistor passing 20ma

r=v/i

r=10 / 0.02 =500ohm

p=iv = 0.02x 10=0.2watts

 

if you have 10 led in parralel:

current required through resistor = 10x0.02=0.2amps

voltage drop is the same

so r=v/i=10/0.2=50ohm

p=iv=0.2x10 =2watts

 

 

i've done the above very quickly, don't blame me if you don't check it and your leds blow up

If you wire in series each led is like a resistor so the more you put on the more the resistant. If you wire in parallel the voltage is the same on all leds, eg 12v carries across all leds.

 

Hope this helps.

Or of course if you wire 7 in series (assuming 14v supply) then no resistors are required at all ;)

Or of course if you wire 7 in series (assuming 14v supply) then no resistors are required at all ;)

Yep

I know something about leds when I made guitars for the stars :D

Right, it's gonna be 15 rows of 5 LEDS wireed in series. The LED details are:

 

Reverse voltage 5.0v

DC forward voltage Typical 1.9v Max2.3v

DC froward current 20ma

 

According to the link AndyP put up I need 56OHM resistor for 12v or 150OHM for 14v, so which do I use?

Right, it's gonna be 15 rows of 5 LEDS wireed in series. The LED details are:

 

Reverse voltage 5.0v

DC forward voltage Typical 1.9v Max2.3v

DC froward current 20ma

 

According to the link AndyP put up I need 56OHM resistor for 12v or 150OHM for 14v, so which do I use?

 

 

think you may have got it wrong, i rekon 120 ohm for 12v and 220 ohm for 14 v would be tempted to go for the 14v option or a value inbetween the two,

try

 

http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng#series

Reckon you got that wrong in some way, I think it's 100 ohm for each row of 5 LEDs.

Reckon you got that wrong in some way, I think it's 100 ohm for each row of 5 LEDs.

 

200 Ohm for each row of 5 wired in series :) When the car is running the battery voltage is 14v, so 4 Volt drop required @ 20mA

 

4/0.02=200

 

:)

Oh and power at that value will be 0.08 watts so to play it safe go for anything 0.1W or higher :)

Watt????

used this to work it out :( http://led.linear1.org/led.wiz

 

So 200 OHM is the one to use for 5 LEDS connected in Series?????

used this to work it out :( http://led.linear1.org/led.wiz

 

So 200 OHM is the one to use for 5 LEDS connected in Series?????

 

Yes :)

used this to work it out :( http://led.linear1.org/led.wiz

 

So 200 OHM is the one to use for 5 LEDS connected in Series?????

 

 

yes, except iirc they don't make a 200ohm resistor so you need a 180 ohm (slightly brighter) or a 220 ohm (slightly dimmer)

Thanks guys, really appreciated :)

Vijay .. u will only need 3 leds in series .. this will give 4v to each LED .. no resistors needed