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I recently bought a WS2812 LED strip (5 meters, 300 LEDs)

When the LEDs are driven at full brightness and each color lit, they draw 60mA each--or 18 amps for all 300!

This led to a problem, which led to a question.

A friend suggested that I not attempt to power the whole strip at once, because even if I could, 18 amps would probably burn it up. So, the other option is to splice in power leads every so often, which is recommended by the manufacturer.

I took a look at my power supply and realized that while it can supply between 0-24vdc, it can only supply 5 amps.

Is there no difference between 12v at 5 amps, and 5v at 5 amps other than power? I understand that Power = amps * volts, so 12v at 5 amps is 60 watts, and 5v at 5 amps is only 25 watts. My question is this: shouldn't the limiting factor be the wattage, not the current? If my power supply can supply 24v at 5 amps (it can), this is 120 watts. In order to supply 120 watts at 5 volts, I would be hitting 24 amps.

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  • \$\begingroup\$ I'm sorry to say but you are mistaken. \$\endgroup\$ – W5VO Oct 16 '16 at 9:51
  • \$\begingroup\$ Since these leds are programmable RGB leds you need a special (DIY) controller to use these leds. A simple power supply does not bring you far. \$\endgroup\$ – Decapod Oct 16 '16 at 10:39
  • \$\begingroup\$ Putting all LEDs in parallel is the worst approach. You should use a combination of series and parallel connection. For e.g. if the LEDs are 3V rated, split the 300 LEDs in 37x8 (total 296) groups. Connect 8 of them in Series along with 1 Ohm 1 Watt Resistance in series. Now 37 of such series connected LEDs+Resistors in parallel. This arrangement would draw roughly 2.3 Amps current at 24V which your supply is capable of delivering. Refer this calculator led.linear1.org/led.wiz to visualize the circuit which I am referring. \$\endgroup\$ – sribasu Oct 16 '16 at 11:36
  • \$\begingroup\$ @W5VO: Thank you for the useless answer. \$\endgroup\$ – tssguy123 Oct 16 '16 at 11:41
  • \$\begingroup\$ @Decapod: I know that. Since I mentioned they are WS2812 LEDs, I'm clearly using a microcontroller (in this case, a MSP430 that I wrote my own library for). \$\endgroup\$ – tssguy123 Oct 16 '16 at 11:42
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You are partially correct. All three: power, current, and voltage are limiting factors for your power supply. If your power supply is labeled 0-24VDC @ 5A max, then it means it can handle these max ratings:

  • Max Voltage: 24V
  • Max Current: 5A
  • Max Power: 120W

So you say your LED's draw 18A total. This is only half of the equation. You also need to know what voltage the strip needs to be supplied. If the voltage that the strip requires is less than 1/18 of 120 (6.67V), then congrats, your power supply can handle your LED strip. If the required strip voltage is > 6.67V, then your total power draw will be > 120W which is no good. However, you can't just willy nilly plug the LED strip into the power supply because remember, your power supply can only handle 5A. The easiest way to overcome this problem is through the use of a power transformer to turn 24V into your required voltage.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ YES! Thank you so much. Sorry, I should have been more specific in my initial post--I figured the WS2812s were common enough to where people would be familiar with them. They require 5 volts. What I find interesting is that the power supply can supply 24vdc at 5amps just fine (120w) but when you turn it down to 5v it can still only supply 5amps, which is much less power. I'm glad to know that it IS possible to turn higher voltage/lower current power into lower voltage/higher current power. I just did not have enough knowledge to realize a transformer is what is needed to do it. :) \$\endgroup\$ – tssguy123 Oct 16 '16 at 11:48
  • \$\begingroup\$ No problem. This might be kind of cheeky to ask, but please upvote if you found my answer helpful :D \$\endgroup\$ – ninehertz Oct 16 '16 at 11:51
  • \$\begingroup\$ way ahead of you :) I don't have enough rep, but I did upvote. \$\endgroup\$ – tssguy123 Oct 16 '16 at 11:55

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