Question about Christmas LED bulbs - HobbyTalk
Reply
 
LinkBack Thread Tools Search this Thread
post #1 of 17 (permalink) Old 12-30-2010, 11:59 AM Thread Starter
Member
 
nautilusnut's Avatar
 
Join Date: Jul 2008
Location: Tupelo, MS
Posts: 379
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.
nautilusnut is offline  
Sponsored Links
Advertisement
 
post #2 of 17 (permalink) Old 12-31-2010, 12:56 AM Thread Starter
Member
 
nautilusnut's Avatar
 
Join Date: Jul 2008
Location: Tupelo, MS
Posts: 379
Question about Christmas LED Bulbs

Hellloooo- anyone out there?

Nary a nibble.
nautilusnut is offline  
post #3 of 17 (permalink) Old 12-31-2010, 11:43 AM
Top Dog
 
Steve244's Avatar
 
Join Date: Jul 2001
Location: Marietta GA. Well Kennesaw, actually. (Cubicle Hell actually)
Posts: 6,776
Send a message via AIM to Steve244
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.
Steve244 is offline  
post #4 of 17 (permalink) Old 12-31-2010, 12:45 PM
Member
 
Join Date: Apr 2005
Location: Tucson, AZ
Posts: 299
Send a message via Yahoo to geminibuildups
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
geminibuildups is offline  
post #5 of 17 (permalink) Old 12-31-2010, 01:56 PM Thread Starter
Member
 
nautilusnut's Avatar
 
Join Date: Jul 2008
Location: Tupelo, MS
Posts: 379
Question about Christmas LED Bulbs

Thankyou very much!
nautilusnut is offline  
post #6 of 17 (permalink) Old 12-31-2010, 03:17 PM
Elder Statesman
 
Dyonisis's Avatar
 
Join Date: Nov 2009
Location: United States of Unamerica - why leave it when you can trash it?
Posts: 1,482
Here, read this: http://led.linear1.org/led.wiz


~ Sick of being the God of still needing to get paid
Dyonisis is offline  
post #7 of 17 (permalink) Old 02-15-2011, 10:45 AM
Elder Statesman
 
DL Matthys's Avatar
 
Join Date: May 2004
Posts: 500
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
DL Matthys is offline  
post #8 of 17 (permalink) Old 02-28-2011, 05:33 PM
Elder Statesman
 
Join Date: Aug 2002
Posts: 1,863
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?
jbond is offline  
post #9 of 17 (permalink) Old 02-28-2011, 06:14 PM
Member
 
USS Atlantis's Avatar
 
Join Date: Feb 2008
Location: Nowhere
Posts: 395
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
USS Atlantis is offline  
post #10 of 17 (permalink) Old 02-28-2011, 07:20 PM
Elder Statesman
 
Join Date: Aug 2002
Posts: 1,863
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.
jbond is offline  
post #11 of 17 (permalink) Old 02-28-2011, 08:12 PM
Member
 
USS Atlantis's Avatar
 
Join Date: Feb 2008
Location: Nowhere
Posts: 395
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
USS Atlantis is offline  
post #12 of 17 (permalink) Old 02-28-2011, 11:33 PM
Elder Statesman
 
Join Date: Aug 2002
Posts: 1,863
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...
jbond is offline  
post #13 of 17 (permalink) Old 03-01-2011, 05:37 AM
Member
 
USS Atlantis's Avatar
 
Join Date: Feb 2008
Location: Nowhere
Posts: 395
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
USS Atlantis is offline  
post #14 of 17 (permalink) Old 03-01-2011, 02:22 PM
Elder Statesman
 
Join Date: Aug 2002
Posts: 1,863
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!
jbond is offline  
post #15 of 17 (permalink) Old 03-01-2011, 05:58 PM
Member
 
USS Atlantis's Avatar
 
Join Date: Feb 2008
Location: Nowhere
Posts: 395
My standard is to put it between the Cathode and the Negative Pole of the power source
USS Atlantis is offline  
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the HobbyTalk forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome