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Resistor Identification?


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#1 the dimmest bulb

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Posted 31 May 2006 - 02:23 AM

I just bought an led ring from acex008, but he didn't know what the forward voltage of the leds in it were. Knowing that the supply voltage is 5.0, and there's 10 leds on the ring, if I knew how many ohms the resistor was, I'd be able to tell really easily what the leds' forward voltage is, right? I found something online about color codes (http://www.aikenamps...orColorCode.htm) and used that with the resistor calculator (http://metku.net/ind...c/index_eng#top). The resistor calculator said I should be using a 10 ohm 10% resistor (that would be brown-black-black-silver, right?) The one I have is brown-black-brown-gold...which would be 100 ohm 5%, right? Would that be the same thing, or rather, produce the same results?

I'll include a pic, in case I worded this confusingly

IPB Image

Ok, to sum it all up. I'm wiring 10 leds with 3.2 forward voltage in parallel on an led ring. Is this resistor (brown black brown gold) going to work (safely tongue.gif)? Thanks smile.gif

Edited by the dimmest bulb, 31 May 2006 - 02:26 AM.


#2 logic02004

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Posted 31 May 2006 - 02:30 AM

i have that same exact jewel ring set-up with that same resistor and mine are 3.3v leds, and i have 10. so yours should work fine

#3 the dimmest bulb

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Posted 31 May 2006 - 02:38 AM

QUOTE(logic02004 @ May 30 2006, 09:37 PM) View Post

i have that same exact jewel ring set-up with that same resistor and mine are 3.3v leds, and i have 10. so yours should work fine


awesome, thanks a bunch smile.gif

#4 logic02004

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Posted 31 May 2006 - 02:49 AM

np have fun

#5 SICKdimension

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Posted 31 May 2006 - 04:41 AM

That looks like a 100 ohm 1/4 watt. If it is, then it might work for a few hours, but eventually the resistor will overheat. Also, 100 ohms is too high and your LEDs wouldn't be as bright. I'd say get the right resistor.

#6 sibrdav

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Posted 31 May 2006 - 07:06 AM

I couldn't see the type of led from the image, but most led's carry 20ma typ. 30ma absolute max.(shortened life) over 1.7v. Using that assumption, I calculated the value of the resistor to be 150 ohms when connected to 10 led's in parallel at 5v. A 100 ohm resistor might be a little too small because it will flow 30ma through the leds. 150 ohms will flow about 23ma and is a standard size available at radio shack.

#7 the dimmest bulb

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Posted 31 May 2006 - 02:36 PM

QUOTE(sibrdav @ May 31 2006, 02:13 AM) View Post

I couldn't see the type of led from the image, but most led's carry 20ma typ. 30ma absolute max.(shortened life) over 1.7v. Using that assumption, I calculated the value of the resistor to be 150 ohms when connected to 10 led's in parallel at 5v. A 100 ohm resistor might be a little too small because it will flow 30ma through the leds. 150 ohms will flow about 23ma and is a standard size available at radio shack.


That doesn't sound right, seeing as how everyone's saying 100ohms is too big. I'm not sure how you got that result, but using the metku resistor calculator (5v power supply, 3.2 forward voltage, 20 ma desired current, 10 leds in parralel) I got 10 ohm 1/2 watt. (Can anyone else confirm that that's right?)...a far cry from 150 ohms.

#8 SICKdimension

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Posted 31 May 2006 - 02:59 PM

Ya, you must have made a mistake in your calculations, sibrdav. Forget to carry the 1? wink.gif

Get the 10 ohm 1 watt resistor.

#9 the dimmest bulb

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Posted 01 June 2006 - 02:12 AM

QUOTE(SICKdimension @ May 31 2006, 10:06 AM) View Post

Ya, you must have made a mistake in your calculations, sibrdav. Forget to carry the 1? wink.gif

Get the 10 ohm 1 watt resistor.


10 ohm 1 watt? I thought it was 1/2 watt? huh.gif so very confused >_<

#10 SICKdimension

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Posted 01 June 2006 - 03:53 AM

3.2v, 20mA, 10 LED, right? Then yes, 1watt. Specifically, you need greater than 0.6watt, so you should always go to the next higher value, which is 1.

#11 the dimmest bulb

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Posted 01 June 2006 - 04:36 AM

QUOTE(SICKdimension @ May 31 2006, 11:00 PM) View Post

3.2v, 20mA, 10 LED, right? Then yes, 1watt. Specifically, you need greater than 0.6watt, so you should always go to the next higher value, which is 1.


I s'ppose that makes sense. I just assumed that because it said .36 for the calculated wattage and .6 for the safe pick, 1/2 watt is what I wanted (greater than .36...and I don't know of a .6 watt tongue.gif). At any rate, thanks for the info smile.gif.

And, if I'm not mistaken, Radio Shack will have some cheap-as-free 10 ohm 1 watt resistors.

Thanks again to everyone that's helped smile.gif




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