PSU for LED strips

[PerfectlyNutz]

Hello, The upcoming question is for people who know a little bit about Power consumption calculation, Addressable LEDs and PSUs.

 

So this is what's going on:

I want to build an Ambilight for my living room TV. I've found that the WS2812B LEDs are best suited for my need. I also need this https://goo.gl/99wSJ8 controller for it so far everything is fine.

I need about 5 meters of a strip with each meter using 18w. The strip I've found functions at 5v. Here's the listing: https://goo.gl/Yf97jn. It says it uses 18w/meter and needs 5v. My question is what power supply do I need?

 

My calculations are:

18w/m for a 5m strip= 90w

Using a 5v connection mean 90w/5v= 18 amperes

Giving 20% headroom means 181.2=21.6 ampere

 

the closest power supply I've found on Aliexpress is 20 ampere or 30 amperes. Given the price difference is only 3 dollars I think the 30amps version is the best. The PSU I've found: https://goo.gl/acju3W

 

BUT It sounds SOO much (22 amperes) for just an LED strip. Is my calculation correct? Am I doing any mistake here? 

 

NOTE: I've found some old power supply I used for some older LEDs I've used once. It has 12v 3 amperes (see picture). If I'd want to use it I'd need to buy the WS2811 Strip (it uses 12v) but again let's say I need 4 meters. SO: 4m with 18w/m= 72w 72w/12v=6 ampere 61.2 (20% headroom)= 7.2 This is more then twice the amount of the power supply I have and if I understand correctly the WS2811 can only control every 3 diodes separately. Will it still look good?

 

 

 

I think I'm kind wrong with everything so please help me.

 

 

[Guest]

Your calculations are correct. And I agree that 20A sounds a lot, but considering how many light's are on that thing, it doesn't surprise me.

36 minutes ago, PerfectlyNutz said:

NOTE: I've found some old power supply I used for some older LEDs I've used once. It has 12v 3 amperes (see picture). If I'd want to use it I'd need to buy the WS2811 Strip (it uses 12v) but again let's say I need 4 meters. SO: 4m with 18w/m= 72w 72w/12v=6 ampere 61.2 (20% headroom)= 7.2 This is more then twice the amount of the power supply I have and if I understand correctly the WS2811 can only control every 3 diodes separately. Will it still look good?

I'd take the 12v one, PSU's for that are probably cheaper and easier to find.

I am not sure about this, but I believe the WS2812B can also control only 3 diodes at the same time.(Please someone confirm)

[Inelastic]

Each led takes 20mA to power at its brightest. There are 3 leds per led pixel for a total of 60mA. If you're buying the 60 pixel/meter type, then that's 18 amps for 5 meters. I'm not sure what you mean by "control every 3 diodes separately." For RGB strips, there's 3 diodes (red, green, and blue) per pixel.

[Stefan Payne]

1 hour ago, Inelastic said:

Each led takes 20mA to power at its brightest. There are 3 leds per led pixel for a total of 60mA.

If you'd connect it in parallel.

But with LEDs you want a couple in series as well. For 12V you could go between 3 or even 4 in series and thus all stay at 20mA.

BUT: Don't forget the current limiting resistor before the LED.

[Stefan Payne]

3 hours ago, PerfectlyNutz said:

If I'd want to use it I'd need to buy the WS2811 Strip (it uses 12v) but again

Get the 12V ones because you can save on the Power Supply because you need less than half the current of the 5V one.

And its the current that makes a PSU expensive, not the Voltage.

 

ie a 5V/24A PSU is way more expensive than a 12V/10A but both could do the same wattage continuously.

And you could also save on the cabeling as you need lower current as well...

[Inelastic]

4 hours ago, Stefan Payne said:

If you'd connect it in parallel.

But with LEDs you want a couple in series as well. For 12V you could go between 3 or even 4 in series and thus all stay at 20mA.

BUT: Don't forget the current limiting resistor before the LED.

If they're staying a constant 20mA, then that would mean they're fully lit all the time right? If the led is turned off, then it shouldn't have any current going through it.

[PerfectlyNutz]

17 hours ago, Stefan Payne said:

Get the 12V ones because you can save on the Power Supply because you need less than half the current of the 5V one.

And its the current that makes a PSU expensive, not the Voltage.

 

Okay. This means I need the WS2811 LEDs if I'm correct. These use 12v. I've checked and you're right. It's way cheaper. Not only the PSU but also the Strip itself. 
But if I'm correct there's only one 1 ic unit for 3 pixels and that means that I can change the lights only in pairs of 3? (meaning the transitions won't look that good?). And does it mean that I also need another PSU for the Arduino because it's 5v and the PSU is 12v? or maybe I can power it using the USB cable? 

Thanks for helping me!