What are the specs for Christmas light LED's?
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Jay.Blanchard
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- Joined: Mon Feb 17, 2014 10:44 pm
What are the specs for Christmas light LED's?
Let's say I want to break up a Christmas tree light set to use the LED's. How do I calculate the specs so that I know which resistor to use?
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greasyspoon
- Posts: 203
- Joined: Fri Feb 01, 2008 11:57 am
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I have never used LED I want and I did some research. Here are some things from post I have found. I can't answer questions but maybe this will help. I can't give credit either I have no idea where I found the info.
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YELLOW, AMBER, RED, most GREEN LEDs tend to operate best at between 1.8 and 2.4 volts.
WHITE, some GREEN, most BLUE LEDs are happiest at between 3.4 and 3.6 volts.
So, take your 6 volts supply voltage, subtract the operating voltage of your LED, allow 0.020 amps for the LED and apply Ohm's law.
6 - 3.4 = 2.6 volts to be 'dropped'.
E=IR or R=E/I or R = 2.6 / .020
or = 130 ohms or a bit more.
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If that PS can't be switched between it's two output voltages, dump it and use either a battery pack or get a new wall-wart.
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I will be using a 9v battery to power them
Ok
R=(9-3.5)/.02 = 275 or 290 ohm - I think that's the next standard - don't have my list in front of me
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Oh, BTW, I'd use a AA pack rather than a 9v battery to power that thing
9v Batteries have a much shorter lifespan compared to a AA or even a AAA pack
Typical 9v rechargable has less than 200 MA - that's 10 hour lifespan for 1 LED
Typical AA rechargable has 2000MA or more - that's 100 hour lifespan for 1 LED
I always use AA rechargables for lighting when I don't use a Wall-wart - you can get packs that hold 2,3,4, or 6 batteries
I'd use the 3 pack for that application and that would work out to be
R=(4.5-3.5)/.02 = 50 or 62 ohm for your standard resistor
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>Bulb type 3.5v/0.07W
>It then says that the transformer supplied is 24v/10.8V output (dont know if that makes any difference )
Well, lets break it down
W=V*A
A=W/V
So .07/3.5 = .02 or 20ma - which is normal for a LED
So to calc the resistance needed for the power supply -> LED
R=(V1-V2)/A
R=(24-3.5)/.02 = 1025 or a 1.2k resistor
R=(10.8-3.5)/.02 = 365 or a 370 ohm resistor
So depending on what your PS is switched to - I hope there's a switch to control the output - you'll need either a 1.2k or a 370 ohm resistor - always go UP in ohm from the calculated to the next available standard
I've gone and hung a meter on the Forever Bright and Phillips LEDs from Christmas light strings and figured the voltage from the resistance necessary to drive the LEDs at 20 mA ( 0.020 Amps ).
Results:
BLUE LEDs (both) - 3.6 Volts at 20 mA
WHITE LEDs (both) - 3.6 Volts at 20 mA
GREEN LEDs (Forever) - 3.6 Volts at 20 mA
RED LEDs (Forever) - 2.8 Volts at 20 mA
ORANGE LEDs (Forever) - 2.8 Volts at 20 mA
YELLOW LEDs (Forever) - 2.8 Volts at 20 mA
___________________________________________________
YELLOW, AMBER, RED, most GREEN LEDs tend to operate best at between 1.8 and 2.4 volts.
WHITE, some GREEN, most BLUE LEDs are happiest at between 3.4 and 3.6 volts.
So, take your 6 volts supply voltage, subtract the operating voltage of your LED, allow 0.020 amps for the LED and apply Ohm's law.
6 - 3.4 = 2.6 volts to be 'dropped'.
E=IR or R=E/I or R = 2.6 / .020
or = 130 ohms or a bit more.
_________________________________________________
If that PS can't be switched between it's two output voltages, dump it and use either a battery pack or get a new wall-wart.
----
I will be using a 9v battery to power them
Ok
R=(9-3.5)/.02 = 275 or 290 ohm - I think that's the next standard - don't have my list in front of me
--
Oh, BTW, I'd use a AA pack rather than a 9v battery to power that thing
9v Batteries have a much shorter lifespan compared to a AA or even a AAA pack
Typical 9v rechargable has less than 200 MA - that's 10 hour lifespan for 1 LED
Typical AA rechargable has 2000MA or more - that's 100 hour lifespan for 1 LED
I always use AA rechargables for lighting when I don't use a Wall-wart - you can get packs that hold 2,3,4, or 6 batteries
I'd use the 3 pack for that application and that would work out to be
R=(4.5-3.5)/.02 = 50 or 62 ohm for your standard resistor
______________________________________________________
>Bulb type 3.5v/0.07W
>It then says that the transformer supplied is 24v/10.8V output (dont know if that makes any difference )
Well, lets break it down
W=V*A
A=W/V
So .07/3.5 = .02 or 20ma - which is normal for a LED
So to calc the resistance needed for the power supply -> LED
R=(V1-V2)/A
R=(24-3.5)/.02 = 1025 or a 1.2k resistor
R=(10.8-3.5)/.02 = 365 or a 370 ohm resistor
So depending on what your PS is switched to - I hope there's a switch to control the output - you'll need either a 1.2k or a 370 ohm resistor - always go UP in ohm from the calculated to the next available standard
I've gone and hung a meter on the Forever Bright and Phillips LEDs from Christmas light strings and figured the voltage from the resistance necessary to drive the LEDs at 20 mA ( 0.020 Amps ).
Results:
BLUE LEDs (both) - 3.6 Volts at 20 mA
WHITE LEDs (both) - 3.6 Volts at 20 mA
GREEN LEDs (Forever) - 3.6 Volts at 20 mA
RED LEDs (Forever) - 2.8 Volts at 20 mA
ORANGE LEDs (Forever) - 2.8 Volts at 20 mA
YELLOW LEDs (Forever) - 2.8 Volts at 20 mA