LEDs in parallel circuit-Keep blowing - LED Wiring

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LEDs in parallel circuit-Keep blowing

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MM3Canuck

Posted: Monday, March 16, 2009 8:31:46 AM

Rank: Newbie
Groups: Member

Joined: 3/16/2009
Posts: 1
Points: 3

Hi!

Im new to this whole wiring LED's thing. But have some basic knowledge!!!

I have 12 LEDs in parallel, here are the numbers:

Power source: 12Volt Motorcycle battery (will be installed on a bike as well!)

LED specs:
Emitted Colour : Yellow
Size (mm) : 3mm
Forward Voltage (V) : 1.8 ~ 2.2
Reverse Current (uA) : <= 30
Luminous Intensity Typ Iv (mcd) : 4000(Typical) ~ 5000(Max)

I used this site to calculate the resistor needed for my 12 LED parallel circuit. http://ledcalc.com/#calc

Values I plugged in:
Supply Voltage: 13.8
Voltage Drop Across LED: 2.2
Desired LED Current: 30 milliamps
How many leds connected: 12

The answer was: 33Ohm - 5Watt resistor.

Everytime I connect the resistor and turn on the power, all LEDs blow instantly. Is the resistor too big? Am I not using the right numbers in the formula??

Any ideas are appreciated.

Dennis

ghpk

Posted: Tuesday, March 31, 2009 3:26:03 PM

Rank: Newbie
Groups: Member

Joined: 3/31/2009
Posts: 1
Points: 3
Location: India

hi,
you should use a resistor for evry 3 L.E.D. in series, I've a similar setup in my car and they are runing fine since a year now.
iam using 3 L.E.D.'s in series and then a 1k resistor (1/4watt) and have 48LED series in 3 each, and using 16 resistors.

for yellow i would just use 3 L.E.D. in series with a 300 ohm resistor and it should be fine.

mscoffman

Posted: Friday, March 05, 2010 6:46:24 PM

Rank: Newbie
Groups: Member

Joined: 2/28/2010
Posts: 5
Points: 15

Hi!

It is absolutely wrong for parallel leds. The calculator probably meant to have all the
leds in series!...That would work out about right...You can use the gentleman's
post above or look at the "I am trying to build my own Led Taillights" post where I
go through the design analysis for the 13Volt case in detail.

When you do a design you should have a way to estimate the approximately correct
values of components so what you did doesn't happen...Oh well, fortunately leds are
inexpensive and leds are rather forgiving devices too.

:mscoffman

jimmy007

Posted: Tuesday, March 09, 2010 3:45:46 AM

Rank: Newbie
Groups: Member

Joined: 3/9/2010
Posts: 1
Points: -94
Location: india

it is so I used this site to calculate the resistor needed for my 12 LED parallel circuit. http://ledcalc.com/#calc

Values I plugged in:
Supply Voltage: 13.8
Voltage Drop Across LED: 2.2
Desired LED Current: 30 milliamps
How many leds connected: 12

The answer was: 33Ohm - 5Watt resistor.

Everytime I connect the resistor and turn on the power, all LEDs blow instantly. Is the resistor too big? Am I not using the right numbers in the formula??

Any ideas are appreciated.

Sterling parts

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