First of all, I don't have much electronic knowledge. I am having trouble connecting the LEDs in parallel.I have two types of LEDs which have different power.Here are some current measurements:

The red LED draws 1A when driven alone. red_alone

The blue LED draws 0.5A when driven alone.


When connecting two red LEDs in parallel: red_red

When connecting two red LEDs and 1 blue LED in parallel: blue_red_red

(1) Why did the 2 red LEDs not draw 2A?

(2) Why 2 red and 1 blue led did not draw 2.5A?

Note:My power supply is 30 volts and 50 amps.

  • \$\begingroup\$ Can you put a link to the datasheets of the red and blue LED modules into the question. \$\endgroup\$ – Steve G Jul 1 at 10:17
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    \$\begingroup\$ Never connect LEDs in parallel, as due to the I-V curve one LED can draw all the current, see electronics.stackexchange.com/a/174585/225159 \$\endgroup\$ – nyronium Jul 1 at 10:20
  • \$\begingroup\$ Have you got the current limiting set to 1.58A on your power supply? \$\endgroup\$ – HandyHowie Jul 1 at 10:59
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    \$\begingroup\$ Usually, no data sheet means no answer = guessing = disappointment or unpredictability. Why buy something from a non-reputable supplier who also doesn't provide enough information to design the circuit properly? \$\endgroup\$ – Andy aka Jul 1 at 11:56
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    \$\begingroup\$ @bopele if you don't have a datasheet, can you at least post a photo of the LED module so we have some idea what it is? Also, how are you measuring the current? What sort of meter? Does it read true RMS current? \$\endgroup\$ – Steve G Jul 2 at 7:45

Because LED (which is a diode) doesn't have a linear current-voltage characteristics and also the power supply's I-V characteristics is not ideal (it's not exactly an I-V vector with slop=0) so adding another LED (which tends to consume more current) makes a tiny slight change in the power supply's voltage and that slight change in voltage is enough to make an observable change in LEDs' currents.

Take a look at the first image. In forward bias slight change in voltage can make a significant change in the LED's current.

(The second image is I-V characteristics of a typical power supply and you can see the slight slope which proofs that a change in supply current makes a change in supply voltage)

LED I-V characteristics

an Example of an LED's I-V characteristics

  • \$\begingroup\$ Welcome to the site :-) When you include something in an answer (e.g. photo, image or text) which isn't your original work, you need to properly reference it, as explained in this site rule. Therefore, since those diagrams appear to be copied from elsewhere, you need to edit your answer and add a link back to the original web page from which each image was copied. Please can you do that? Thanks. :-) (I recommend that you also read the tour and help center to learn more about this site.) \$\endgroup\$ – SamGibson Jul 1 at 18:13

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