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I've come across an interesting irregularity while designing a arduino LED controller. I wanted to measure the current draw of my LED strip to determine power requirements. I was curious as to which color was drawing the most power, and I noticed that when measuring the colors individually the current did not add up to the current measured when combined.

Here is the data I recorded, all measurements are in Amps.

12V Supply 1A    4A

G       0.88    0.97

R       0.53    0.56

B       0.68    0.76

GR      1.2     1.35

GB      1.24    1.44

RB      1.03    1.16

RGB     1.48    1.75


G+R+B   2.09    2.29

The single characters R G B are the individual colors measured, the double characters are the combination of two colors measured together, and the RGB is the measurement of all three colors at the same time.

There is a substantial difference between the individual measurement for R+G+B and RGB. Is this some characteristic of RGB LED?

Also, I tested the current with two power supplies, one is rated for 1A, but is showing a draw of 1.48A. Is is more likely that the supply is underrated, or is it more likely that it is broken?

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    \$\begingroup\$ A schematic and if you marked where / how you made your measurements, it might help. \$\endgroup\$ – Tyler Feb 15 '18 at 23:40
  • \$\begingroup\$ Possibly the effects of voltage drop on the ground wire. And as for your power supply question - that power supply doesn't have current limiting and you are overloading it. \$\endgroup\$ – user253751 Feb 15 '18 at 23:51
  • \$\begingroup\$ the 1A power supply values are bogus. you should not have included them. \$\endgroup\$ – jsotola Feb 16 '18 at 1:31
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    \$\begingroup\$ the values are probably different because the LED controller in the LED module adjusts the brightness of each color depending on which colors are lit \$\endgroup\$ – jsotola Feb 16 '18 at 1:37
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You will need to also measure the voltage at the supply output. There is a good chance that at higher current demand that you were overloading the poser supply causing its output voltage to be dragged down to below the 12V that you think it is providing.

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LED strips have one problem : the voltage drop over the strip can be considerable. When having long strips or high current going thru the strips you will have more losses.

When using individual colors the common rail on the strip (mostly the +12V) has less trouble feeding the current but once you add another color or even use all colors the common rail on the strip is having a hard time.

Most strips come on 5 meter rolls but its not the best practice to use them in one piece especially the cheaper ones.

Try a shorter strip and if you must use a longer piece you might consider feeding it from both sides.

PS : check the voltage over the whole length of the strip (moving both leads up and down the strip) you will see that there are considerable losses.

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A more accurate measurement would take the end of reel voltage and compare with source voltage . Since there must be a series R in each colour string of 3 LEDs for a 12V string. There is at least 3 V drop to limit the current. If the voltage drops 0.3V on average or 0.6V at the end, then the current will drop 10% then a driving RGB full will cause even more loss they RGB will never add up to R+G+B.

Feeding power to both ends may help, but our eyes may not see much difference in brightness from one end to the other. However, if they were adjacent pixels on a TV, you can notice it but the further away it is , the hard it is to tell.

In any case, chalk it up to cheap stripled flex circuit tracks. (too thin + lightweight )

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