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How to Determine Current (amperage) Draw for LED Strips Answered

I have some warm white solid color LED strips. The packaging doesn't say anything about their current draw (neither amperage or "watts"). The strips themselves are marked as 12VDC. I want to use a wall wart to power a strip of lights but I think I need to know how many amps they will draw in order to select the right wall wart.

Is there any way that I can find out the current draw either online or by using a multimeter?

For example, I have a wall wart that converts 110-120VAC to 12VDC that is marked for 5 amps. I don't want to overload the circuit and create problems but without knowing how many amps per foot the LED strip draws, I'm reluctant to make an installation.

I'm uncertain that I'm even asking the right questions. I'm just learning a little about electricity and electronics (Thank you, randofo) by taking classes here. I've learned in my 7-1/2 decades of life that a little knowledge can be a dangerous thing; so I'm asking help from the cognoscenti at Instructables.com

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PKM

7 months ago

You can Google for the product name you have and "amps per meter", or "watts per meter" and divide that by 12? Even if it didn't come with any documentation someone online might know. If you're lucky you'll find a site like this that does the calculations for you http://www.ledlightsworld.com/page.html?id=38

You could cut a short section, say 1m, and connect that to your wall wart with a multimeter set to amps in series with it. There's no way a 1m section will draw 5 amps so you'll be fine, your wall wart will happily power any demand up to 5A. (Some people worry that "my LEDs only need 1A but my supply puts out 5, will it blow up?" to which the answser is "no" - apologies if you already know this isn't how amps work)

Or you could guesstimate, as iceng says: each individual LED will use something like 10 to 20 milliamps, so if it's 3 LED in series and 60 LEDs per meter that would be (60/3)*20mA = 400 milliamps or 0.4A per meter, so you could probably power 10m of strip with your 5A supply.

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icengPKM

Answer 7 months ago

Not everyone could read between my lines so easy PKM..

As you point out the net will give you answers.

If only one slow down and reflect on what is read-ily avail-able.

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iceng

7 months ago

First, you need to verify if your LED Strip is 3_leds_in_series

OR 2_leds_in_series => see the picture..

Look at the number of LEDs between Resistors.. I'm assuming yours is Three..

Sub-note ( If you have a microscope or magnifying glass you could read the Resistance Code )

Then I could give you an exact current at 12 volts..

Now, count the LEDs divide by 3 should be an even number

and multiply 0.01 amperes for a minimum_current and double that for a maximum_current..

BTW if it is too bright you can run the Strip at a lower voltage like 10VDC or 9VDC at some voltage it wont light at all..

Copy of pics 012.jpg