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  #1  
Old 12-30-2010, 10:59 AM
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Question about Christmas LED bulbs

I'm a total novice at LED's in models. After Christmas I bought some LED replacement lamps for Christmas light strings. I got 10 clear bulbs for 63 cents. (Both warm and cool whites) The larger ones are 5mm and the smaller are 2mm. The only specs I see on the packaging is 3.3 volts 0.066 watts.

Question? what resistors to use? I see piles on ebay- I'd like to use a 9 volt battery with snaps for size reasons. A battery pack with a couple of AA's is also good. Any one ever have any experience with these LED's? The price is right- I'm just in the dark as to how to use them.
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Old 12-30-2010, 11:56 PM
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Question about Christmas LED Bulbs

Hellloooo- anyone out there?

Nary a nibble.
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  #3  
Old 12-31-2010, 10:43 AM
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Using ohms law (really this handy calculator), we can see that .066 watts at 3.3 volts requires 20mA.

To achieve 20mA with 3.3 volts across the LED with a 9V source you would need a resistor.

The size resistor is most easily calculated with this handy calculator that suggests 330ohms. This is wiring one resistor per LED.

330ohms is what I typically use.
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Old 12-31-2010, 11:45 AM
geminibuildups geminibuildups is offline
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If you use a small battery pack with 2 AAA (3v) it will take up less room and you will not need a resistor.

Geminibuildups

GEMINI MODEL BUILD-UP STUDIOS
www.geminibuildupstudios.com
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Old 12-31-2010, 12:56 PM
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Question about Christmas LED Bulbs

Thankyou very much!
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  #6  
Old 12-31-2010, 02:17 PM
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Here, read this: http://led.linear1.org/led.wiz


~ Sick of being the God of still needing to get paid
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Old 02-15-2011, 09:45 AM
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It is a good deal to "mine" for regular white LEDs off of Xmas light strings.
I disassemble the string to get to the LED in original configureation and away from the resistores that works the string with house current.

A post holiday sale can get up to 80-100 LEDs for pennys on the dollar.

I would encourage to use lower voltages near the value of the LEDs from a battery source other than 9 Volts. Most colored LEDs work at 2.5v 25ma, most white LEDs work at 3.5 volts 30ma. Lower resisters will throw off less heat in your new LED string.

DLM
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Old 02-28-2011, 04:33 PM
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I got an 18-bulb Philips LED set that comes with a battery pack--takes 4 AAs. The battery pack is too bulky for where I want to put it--I cut it off and tested a 9 volt battery on it, which runs the LEDs nice and bright. I hooked that up for 5 minutes, seemed to run a little warm and one LED had a slight flicker to it. I doubt I would have the lights on this model lit for more than 5 minutes at a time but any reason I should NOT go with the 9 volt battery?
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Old 02-28-2011, 05:14 PM
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Quote:
Originally Posted by jbond View Post
I got an 18-bulb Philips LED set that comes with a battery pack--takes 4 AAs. The battery pack is too bulky for where I want to put it--I cut it off and tested a 9 volt battery on it, which runs the LEDs nice and bright. I hooked that up for 5 minutes, seemed to run a little warm and one LED had a slight flicker to it. I doubt I would have the lights on this model lit for more than 5 minutes at a time but any reason I should NOT go with the 9 volt battery?
Go ahead, but put resistors in there - if the LED's are running warm, and you got that flicker - you're chancing a blow-out = Dead LEDs

LED's are fickle beasts in one respect - they can run at higher than recommended voltage for a time, but you'll get no warning when they're going to die - could be 10 seconds, could be 20 hours; no way to tell beforehand and they could run fine for 5-10 minutes one day, then blow in 2 seconds the next

Better to run them under and a little dim than over and have a blow-out after the model is sealed up
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Old 02-28-2011, 06:20 PM
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That's good advice but what kind of resistors and where do they go? I basically have (I assume) a positive and negative wire coming away from the bundle of LEDs now that I've cut the battery box off.
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Old 02-28-2011, 07:12 PM
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Are you separating them out, or using the string as a whole - or taking part of the string

Also I need to know how the LEDs in the string connect to each other

Looking at the bottom of the lens, you MAY see a flat spot in the circular base just above where the wires enter the LED itself

The flat spot marks the Cathode (negative post) - the other side is the Anode (positive post)

Do the LED's in the string connect

Cathode - Cathode - Cathode
or
Cathode - Anode - Cathode

Necessary to determine what value resistor to use
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Old 02-28-2011, 10:33 PM
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I want to keep the string intact--there are actually three wires connecting to every LED except for the last two--those have two wires each. And I can't see anything to indicate which is cathode and which is annode...
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Old 03-01-2011, 04:37 AM
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Ok, well keeping the string intact does help a bit - we'll have to assume that there's internal voltage dropping to cover the 6v

What we need to do is drop the 9v to 6v - we'll also consider that the LEDs are 20ma current draw; this results in the largest resistor value for standard LEDs

So, I'd put a 150ohm resistor in that circuit to drop the 9v source to the 6v that the string was using
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Old 03-01-2011, 01:22 PM
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Great--so does it matter where the resistor is placed in the chain? Obviously I'm going to have the battery and an on/off switch connecting the two wires coming out of the LED bundle. This is very helpful--thanks!
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Old 03-01-2011, 04:58 PM
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My standard is to put it between the Cathode and the Negative Pole of the power source
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