Paul TigerB6
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| posted on 2/4/08 at 03:25 PM |
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wiring in LED's
Does it make any difference where in the circuit the resistor is placed (before or after the LED)??
ie, +12V - LED - Resistor - earth
or +12V - resistor - LED - earth
Simple one but cant find a definate answer
Cheers
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Macbeast
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| posted on 2/4/08 at 03:27 PM |
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Definitw answer - no 
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Mr Whippy
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| posted on 2/4/08 at 03:28 PM |
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if there was a power surge  the resister would blow and save the diode
Fame is when your old car is plastered all over the internet
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Paul TigerB6
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| posted on 2/4/08 at 03:29 PM |
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Sorted!! Thanks
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BenB
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| posted on 2/4/08 at 03:36 PM |
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No difference.
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02GF74
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| posted on 2/4/08 at 03:43 PM |
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quote:
Originally posted by Mr Whippy
if there was a power surge the resister would blow and save the diode
I'm afraid I disagree. Have you looked at the die inside a LED and see how thin the tiny gold wire to it is? That will be the fuse should
there be a power surge. When is does go, often the plastic cover gets blown off too
Interesting question though - I cannot recall ever seeing it wired other than:
12V --- resistor --- LED --- 0 V
yet at this moment cannot think why the other option is not used; maybe it is and I have never really noticed/considered it.
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jlparsons
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| posted on 2/4/08 at 05:22 PM |
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I have to say I think the resistor would not save the LED, it will limit the current that will flow at 12V to a level that's safe for the LED
but if you suddenly had a voltage surge from an electrical fault it would allow a proportionally higher current, potentially enough to blow the LED.
You'd need to know the safe amps limit of the led and fuse it to that level, i'm not sure if there's any point though...?
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
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jlparsons
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| posted on 2/4/08 at 05:22 PM |
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I do of course reserve the right to be completely and utterly wrong.
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
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Paul TigerB6
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| posted on 2/4/08 at 05:26 PM |
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Well i have wired in the LEDs the other way around to the "norm" now as I had already done the circuit board with the resistors on
"the other way" and wasnt about to change it unless i had to. If an LED does blow then a new one is 19p and a few mins soldering so not
enough to worry about.
Martin who i am building the car for is an electrician so i think he'll be fine.
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martinq357
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| posted on 2/4/08 at 07:38 PM |
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Just found this:
http://www.kpsec.freeuk.com/components/led.htm
Hope it helps.
Martin.
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Mr Whippy
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| posted on 2/4/08 at 08:07 PM |
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quote:
Originally posted by martinq357
Just found this:
http://www.kpsec.freeuk.com/components/led.htm
Hope it helps.
Martin.
good find. Anyone know why blue LEDs are so dazzling even at a distance with a big halo around them? I suspect it is the short wavelength light
refracting inside the moisture on the surface of the eye.
Fame is when your old car is plastered all over the internet
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hillbillyracer
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| posted on 2/4/08 at 10:13 PM |
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Or you could just get 12v LEDs from the likes of Maplin. 30-40 pence & no resistor to worry about!
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Paul TigerB6
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| posted on 2/4/08 at 10:15 PM |
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Know what you mean Mr Whippy. My old car got LED's fitted (by me) when i fitted a carbon dash and the main beam warning was blinding!! I changed
the resistor so many times to turn the brightness down but still dazzled me.
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trikerneil
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| posted on 3/4/08 at 05:38 AM |
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I have found this LED ARRAY WIZARD useful in the past.
Neil
ACE Cafe - Just say No.
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Paul TigerB6
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| posted on 3/4/08 at 06:50 AM |
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quote:
Originally posted by trikerneil
I have found this LED ARRAY WIZARD useful in the past.
Neil
Now that is really useful. Draws out the wiring diagram too and puts the resistor after the LED which is how I have done it myself - grounding via the
MegaJolt.
cheers
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Macbeast
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| posted on 3/4/08 at 07:59 AM |
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LED array wizard is brilliant !!
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02GF74
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| posted on 3/4/08 at 09:48 AM |
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quote:
Originally posted by Mr Whippy
Hope it helps.
good find. Anyone know why blue LEDs are so dazzling even at a distance with a big halo around them? I suspect it is the short wavelength light
refracting inside the moisture on the surface of the eye.
there is loads out there on the web about wiring LEDs and computing current limiting resistor value - as yet all have the resistor between + V and
LED.
to answer the Mr W question, it has something to do with the eye sensitivty - is is not very good with blue - there are much less blue cones (about
100x?) than for the red/green plus the cornea absorbs light at higher frequency i.e. blue end of spectrum - dunno the exact details though.
you also shold see a "halo" with red LEDs - something do with the wavelength being in a narrow band.
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