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I just bought a cheap LED strip from China. The used LEDs are from the SMD5630 type. Each meter has 60 LEDs, so 300 LEDs for 5m. The voltage is 12V.

From what I found, the current for 1m should be around 1A (12W / meter). I connected 5m on a power supply that is rated 120W (10A x 12V).

I wanted to make sure that everything is okay. So, grabbed a multimeter and measured the voltage wich is around 11V. Then I measured the current as following: 1 wire from the power supply to the multimeter, from the multimeter a wire to the LED strip, and the other wire from the LED strip to the power supply. This gave me only 1A.

This would mean a power consumption of only about 11W. This sounds very strange to me, as the LEDs are quite bright.

I guess there is something wrong. Any suggestions?

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  • \$\begingroup\$ Why do you think the current for 1m should be 1A? \$\endgroup\$
    – Majenko
    Dec 18 '16 at 15:19
  • \$\begingroup\$ @Majenko I found those values for a typical SMD5630 LED of 1M. 12V multiplied by 1A, gives around 12W/meter. 5 meter would be around 60W, 10meter 120W. \$\endgroup\$
    – Write Down
    Dec 18 '16 at 15:22
  • \$\begingroup\$ But obviously that rating is wrong for your strip. You should examine the strip closely and work out the actual LED arrangement, and find the resistance of any series resistors. Then you can make assumptions about the typical forward drop of an LED based on the colour, and calculate the expected (rough) current. \$\endgroup\$
    – Majenko
    Dec 18 '16 at 15:26
  • \$\begingroup\$ Just because someone else has a car the same colour as mine it doesn't mean they get the same MPG. You need to examine your strip and ignore other people's different strips. \$\endgroup\$
    – Majenko
    Dec 18 '16 at 15:27
  • \$\begingroup\$ @Majenko That is indeed right, and I will check them in more detail. But anyway, 1A for 5M is not that much, right? \$\endgroup\$
    – Write Down
    Dec 18 '16 at 15:43
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While the leds may be 5630 sized, the die size on the led is important too. Some are not full sized and are essentially putting a weaker led in a bigger package to pad their profit. Not all 5630 run at 50 mA either, which is what 60 / 3 in series per 1 meter at 1 Amp comes out to. Standard 5630 are 150 mA diodes, etc etc.

quickest way to test this is to measure the voltage across the resistor for one 3 led section. I = V/R. This tells you the current through the resistor and since current is the same in a series circuit, tells you the current of one 3 led section. Multiply up for what you should get.

At 1 Amp for 5m/300 leds means 1 Amp / 100 segments = 10 mA per segment. Incredibly low. You may have gotten duped.

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Based on area and power rating (5.6*3.0)*0.5W/(5.0*5.0*0.24W) the SMD5630 LED is one and a half more the brightness of a SMD5050 in theory. In practise it depends on chip efficacy.

However unless you have a decent heatsink on Kapton film the chip cannot be driven at 150mA without a significant junction temp rise at 200'C/W or 100'C rise with 0.5W !! Thus 50mA to 70mA is ok.

the 0.5W rating taken from Samsung's LM561B - 5630 Middle Power LED for High CRI BUT thhis requires a heat sink to reduce from 20'C/W to 50'C/W thus I expect this design to only use 50mA per 3S string.

Consider you measured 1A/m @12V or 12W/m or 12W/20P3S/m means 1A/20P = 50mA per string.

If you run from 14.2V supply such as car alternator on a 12V car system, then you can expect 1.5A/m since (14.2-9V)/(12-3*2.83V)=~5.2/3.51=1.5x enter image description here

So it is with normal design expectations adn you may be able to drive from 14.2V with 50% brighter.

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