wiring in resistors

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03-12-2009, 07:13 PM

#11

97modifiedmustangGT

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yeah i actually didn't have the led when i made the original post so i didn't know it was 25 A either. the max volts is 3.6v and the normal, i guess is what you would call it, is 3.3V. i will do some testing tonight when i get home and see if i actually was right. if not, back to buy some 99 cent parts lol

edit: they are 1/4 watt resistors that i picked up

03-12-2009, 11:29 PM

#12

vanquish

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yeah let me know how it goes.

03-13-2009, 01:40 AM

#13

sk8erdudex

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http://ledcalc.com/

Enter in 12V, 3.3V and 25 Milliamps It tells you to get a 390 Ohm Resistor rated at 1/4 Watts

The rating is the wattage that the resistor can handle before it fails.

03-13-2009, 11:07 AM

#14

97modifiedmustangGT

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okay let me know if i am right, when you go to that calculator it asked for the voltage drop across the LED which would be 8.7 since 12-3.3=8.7. It looks like you put in 3.3 for the voltage drop which gave you the 390ohm. when i did it, it gave me 150ohm and1/8 watt.

Anyway i got home last night and soldered up a 330 resistor to the led and connected it to a batter and it worked so i must have done something right. But that calculator makes me think i need something different now. BTW i hate soldering!!!!!!

EDIT: grrrr i really need to look at things more closely. you were right man sorry

Last edited by 97modifiedmustangGT; 03-13-2009 at 11:12 AM.

03-13-2009, 11:54 AM

#15

vanquish

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sk8erdudex that site helps a lot thanks. It's nice to know the calculations behind it too and I think we finally kind of figured it out in two pages of posts. Glad you got it working 97modifiedmustangGT.

03-13-2009, 11:58 AM

#16

97modifiedmustangGT

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give mustangforums a couple pages and we can figure out anything

I just wonder why that site didn't pop up when i did a million searches on google.

03-13-2009, 12:00 PM

#17

sk8erdudex

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97modified, when you place the cursor over the question mark next to the 'voltage drop across LED' it describes that it's the voltage required to power the LED, which in your case is 3.3v

Keep in mind also that resistors have a ±10% margin of error. So if it's not the exact resistance, it's ok. They only make resistors in certain ohm amounts.