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Months ago I bought 3 RGB led strip (1 meter, 60 leds) and now I want to use it on a project.

The specification said

DC5V

18W/m

I struggle with the power supply and the type of circuit I need for this, series vs parallel. If I choose series circuit :

3 * 5V = 15V

3*18W = 54W and then 54/15 = 3.6A

I found a laptop power supply with 15V and 4A, how can use it with my circuit ?

With parallel circuit :

5V

3.6A * 3 = 10.8A

What is the best solution to connect the 3 strips together ?

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If these LEDs have electronics integrated to control the brightness of the individual LEDs independently, connecting them in series is not an option for a number of reasons (data signals to control the brightness will need to be at the same voltage, for one). In such a situation, your calculation of 10.8A @ 5V is correct for 3 meters of strip.

It's worth noting that the power (18W/m) sounds like a maximum rating. In general, the power consumption at any point in time will depend on the brightness of the individual LEDs.

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  • \$\begingroup\$ Thank you for these clarification. Indeed my strip has data (din) to control color of each led (WS2812B). What happens if I plug a 5V >11A power supply ? The led take only the necessary current or they will overheat ? \$\endgroup\$ – Tsuuki Apr 5 '18 at 6:46
  • \$\begingroup\$ A 5V supply rated for 11A should be fine. Most power supplies try to provide a constant voltage and the load will draw what it draws. If the load tries to draw more current than the supply can provide, the supply might overheat or cut out or something like that. Some LEDs use constant current supplies (that change the voltage to force a certain current through the load) but for the WS2812 LEDs, there are integrated electronics in them that handle regulating the current. \$\endgroup\$ – AntaresAdroit Apr 6 '18 at 22:36

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