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Old 05-17-2012, 01:27 AM   #1
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LED rope light voltage question


Hi All,

I'm new here. First post to the site. I have search but can't find exact question I have in mind.

I want to use those "rope LED light" - those sold as a pack of 5 meter(or 16 feet). The type of LED's are called 5050; supposed to run on 12V DC. It just happened that I have a few old laptop power supplies with DC output at 18.5V; 3.5A (65Watt). Can I use these to power the rope light? Or do I have to add a resister? or voltage regulator to drop the voltage?

Is there such a thing as "tolerable" voltage for the LED?

Hope you can give me some pointers. Thanks in advance.

Shang

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Old 05-17-2012, 02:22 AM   #2
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LED rope light voltage question


If it's 12vdc then any 12vdc source will work as long as the amperage is the same or higher than what it uses. It will only draw what it needs.

If you plan to have a lot of these I would look at using a computer power supply. But check how much current it requires, if it's under 1a then an adapter will do, as lot of them are rated at 1a or so. Check to make sure though.

Sometimes you have to add a resistor, so check the light's instructions to see what it says. My guess is it would have it built in.

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Old 05-17-2012, 06:02 AM   #3
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LED rope light voltage question


All semiconductors (INCLUDING LEDS) are sensitive to voltage.
Too much voltage will damage them.
You should use a resistor.
Make sure you do the math,
and make sure the power rating of the resistor
is adequate for the task.
Do you know the currant draw of the led string ?
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Old 05-17-2012, 11:26 AM   #4
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LED rope light voltage question


Quote:
Originally Posted by dmxtothemax View Post
All semiconductors (INCLUDING LEDS) are sensitive to voltage.
Too much voltage will damage them.
You should use a resistor.
Make sure you do the math,
and make sure the power rating of the resistor
is adequate for the task.
Do you know the currant draw of the led string ?

3a for 5 meters. I'll probably use only 4 meters.
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Old 05-17-2012, 03:14 PM   #5
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LED rope light voltage question


Quote:
Originally Posted by shangh View Post
Hi All,

I'm new here. First post to the site. I have search but can't find exact question I have in mind.

I want to use those "rope LED light" - those sold as a pack of 5 meter(or 16 feet). The type of LED's are called 5050; supposed to run on 12V DC. It just happened that I have a few old laptop power supplies with DC output at 18.5V; 3.5A (65Watt). Can I use these to power the rope light? Or do I have to add a resister? or voltage regulator to drop the voltage?

Is there such a thing as "tolerable" voltage for the LED?

Hope you can give me some pointers. Thanks in advance.

Shang
Using this
http://www.wayjun.com/Datasheet/Led/...0SMD%20LED.pdf
there are several ways to wire an LED string that operates on 12v and 3A.
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Old 05-18-2012, 06:05 PM   #6
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LED rope light voltage question


If 5m is 3a,
Then 4m is 2.4a,
16.5V - 12V = 4.5V,
So 4.5v / 2.4a = 1.8 ohms.
Now for power rating,
4.5v x 2.4a = 10.8w.

Thats a lotta power to dissapate !
Two 3.9 ohm 10watt resistors in parrallel should do it !
But they will run mighty hot !
So take care how and where you mount them.

Using a six volt lamp of around 15w,
is another option, ionstead of the resistor.
But it will run warm too,
But at least you could put it to work somewhere!

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