led wiring

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garrytd4

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Now I'm not the sharpest knife in the draw when it comes to electrics, not even the basics. So here goes:
I want to daisy chain some 5mm green leds and run it from 12v. However I'm not sure of where, how many, and what value resistors i need and if I need a fuse.
Read on and see if I'm correct.

12v supply (positive wire) - ??fuse?? - resistor(s) - led-led-led-led-led-led-led-led - back to earth/negative (I also need a switch inthere somewhere)

That's 8 leds I want on a chain. So does that i need 8 resistors? If so, do i put one before each led or all 8 before the leds?

This may soynd like q dumb question to some of u folk but like I say, not the sharpest tool.

I hope this can be understood by someone.
 
Last edited:
LEDs want a couple of volts across each depending on the colour. White one's will take about 3 1/2 volts before they blow so you can probably wire four in series then two lots of four in parallel and you won't need the resistor if your alternator output is OK. Assuming high power LEDs of about 1watt then to play safe a 2 ohm resistor in series with these will protect the lot without losing too much brightness.
 
I was thinking of doing something similar to mine to replace the bulbs that illuminate the dash clocks ( the holders have fallen apart) can you let me know how you get on?
 
garrytd4 said:
Now I'm not the sharpest knife in the draw when it comes to electrics, not even the basics. So here goes:
I want to daisy chain some 5mm green leds and run it from 12v. However I'm not sure of where, how many, and what value resistors i need and if I need a fuse.
Read on and see if I'm correct.

12v supply (positive wire) - ??fuse?? - resistor(s) - led-led-led-led-led-led-led-led - back to earth/negative (I also need a switch inthere somewhere)

That's 8 leds I want on a chain. So does that i need 8 resistors? If so, do i put one before each led or all 8 before the leds?

This may soynd like q dumb question to some of u folk but like I say, not the sharpest tool.

I hope this can be understood by someone.
Click to expand...
Done similar myself working on 1.5V each so 8 is OK for 12V with no resistors and leaves a margin for alternator. Got mine here 100 x 5mm Flat Top white LED Wide Angle light 20000MCD items in bestshop2008hk store on eBay! dirt cheap if you can wait a few days.
Dont forget LEDs are polarity sensitive :eek:
 
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ive tried 8 in a row and all 8 blew, didnt use any resistors, so ive ordered more LEDs and resistors and will try again, so my guess is 12v was too much hense needing the resistor to RESIST too much voltage going to LEDs am i right?
 
garrytd4 said:
ive tried 8 in a row and all 8 blew, didnt use any resistors, so ive ordered more LEDs and resistors and will try again, so my guess is 12v was too much hense needing the resistor to RESIST too much voltage going to LEDs am i right?
Click to expand...

no
 
Green leds should cope with 2v across each so 8 in series should be OK. Did you wire them up then right way round?
 
quick diagram showing how i did it. where am i going wrong?

feel free to slate me if its wrong.

led.jpg
 
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