Non home inspection related electronics question.

Originally Posted By: cfuoco
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I am installing 5 of these LEDS in series from a 12 volt power source. Can anyone tell me what size resistor I need?

http://www.theledlight.com/pdf/042004/YZ-R_3mm_red.pdf

Originally Posted By: bking
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You need a resistor in series with those 5 leds rated at 2 to 5 ohms and one half watt.

Originally Posted By: cfuoco
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Thank you Bruce

Originally Posted By: Greg Fretwell
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Doesn’t sound like enough ohms to me.

Leds drop about 2 v and you end up with 2 at the end, across 2 ohms is 1 amp. That’s 2 watts. I would start with 50-100 and see if they are bright enough. A LED needs about 15ma to be usable.

Originally Posted By: bsumpter
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Using OHM’s law, if you know the Voltage, divide it by the Amperage, and the result is the resistance needed to complete the circuit.

Ohms Law is a mathematical equation that shows the relationship between Voltage, Current and Resistance in an electrical circuit. It is stated as:

V = I x R

R = V / I

I = V / R

Where

V = Voltage

I = Current (I stands for INTENSITY)

R = Resistance

Hope this helps somewhat !

--
"In the fields of observation, chance favors only the mind that is prepared"

Louis Pasteur

Originally Posted By: bgriffin
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This will calculate for multiple LEDs in series.

Bud

Originally Posted By: phinsperger
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Using Bud’s link I came up with 10 ohms 1/4W

.

Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
here !

Originally Posted By: bking
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The specs ref. in the question said 2.3v per LED and 50ma current

using the resistor calc. from Bud, it says 10 ohms 1/4 watt

its not that critical for LED's, depends on the brightness you want.

You can use 5 to 20 ohms and be ok, I would use a 1/2 watt instead of a 1/4 though for good measure.