Powering led strips

[Lax__]

Hi, I am planning on swapping out the LEDs in my RGB fans for 144/m ones, and also using the old ones out of the fans in the case. At full power this would draw around 16 amps, but won't be running at full power. My PSU is the thermaltake smart 700w and can provide 17a on the 5v rail. I am also planning on using an external power supply to power some of the LEDs. So, my question is how much can I safely draw from my PSU, and is there a better way to power all of these LEDs? Thanks in advance.

[Hackentosher]

Well it's thermaltake so idk how accurate that 17 amp rating is, but ATX PSU design is pretty good nowadays even at the lowend. It's probably fine, and your LEDs will probably pull less than your quoted 16 amps. If it is too much for the supply, it will trip over current protection and shutoff.

 

16 amps sounds like a lot to me. I had a strip of about 130 LEDs and it pulled like 4 amps on full white. Unless you're using 4M of LEDs in your case, I doubt you will hit 16 amps.

[Lax__]

6 hours ago, Hackentosher said:

Well it's thermaltake so idk how accurate that 17 amp rating is, but ATX PSU design is pretty good nowadays even at the lowend. It's probably fine, and your LEDs will probably pull less than your quoted 16 amps. If it is too much for the supply, it will trip over current protection and shutoff.

 

16 amps sounds like a lot to me. I had a strip of about 130 LEDs and it pulled like 4 amps on full white. Unless you're using 4M of LEDs in your case, I doubt you will hit 16 amps.

Thanks for replying. It is going to be 1.5 metres of neopixels at 30/m and 1.5 metres of ws2812b at 144/m, making a total of around 261 LEDs. Assuming the max each led will draw is 60ma, the max should be 15.6 amps. They won't be on pure white so shouldn't draw that much, but better to overestimate than underestimate. I was planning on powering it with a molex, and from what I have read, molex connectors can provide  a maximum of 11a on the 5v and 12v pins, so this wouldn't be enough. And won't other components be running off the 5v rail, so it wouldn't have 17a just for the LEDs?

[Hackentosher]

16 hours ago, Lax__ said:

Thanks for replying. It is going to be 1.5 metres of neopixels at 30/m and 1.5 metres of ws2812b at 144/m, making a total of around 261 LEDs. Assuming the max each led will draw is 60ma, the max should be 15.6 amps. They won't be on pure white so shouldn't draw that much, but better to overestimate than underestimate. I was planning on powering it with a molex, and from what I have read, molex connectors can provide  a maximum of 11a on the 5v and 12v pins, so this wouldn't be enough. And won't other components be running off the 5v rail, so it wouldn't have 17a just for the LEDs?

Again, I really doubt this array will pull more than 10 amps. If you already have the LEDs, set them up on a different supply and measure the current draw.

[mariushm]

Your computer power supply can output some current on 5v and some current on 3.3v  but all together COMBINED on the two voltages there's a maximum watts value.

For example, the psu may output 20A on 5v (20x5=100w) and 20A on 3.3v (20x3.3 = 66w)  but COMBINED there may be a 120w limit. 

Yeah, looking at Thermaltake Smart RGB 700w label, you can see it :

 

 

If you power your computer using this same power supply, expect your system to consume 3-5A on 3.3v and 3-5A on 5v , powering various stuff on the motherboard (chipset, onboard network, audio etc) and SSDs, electronics on mechanical drives etc

So if you reserve 5A on 3.3v and 5v for your computer, that leaves you with 120w - 5v x 5A - 3.3v x 5A = 120 - 25 - 16 = 79 watts... Let's just round it to 80 watts.

This means that you'll have 80w / 5v = 16A of current on 5v available, in theory.

However, because the power supply can give a maximum of 17A on 5v and you reserved a 5A budget for the computer, you're left with maximum of 12A on 5v for led use ... or 60 watts.

 

At maximum brightness, each led will consume up to 60mA ... you have around 15-20mA per color in the leds... typically red will have less current because human eyes are more sensitive to it and the chemicals used in the led to produce red can produce enough color and light with less current. 

Anyway... you could average out to around 40mA per LED, assuming you won't set all the leds to FULL WHITE 100% brightness.

 

Another thing... the led strips will have to be "glued" to the case or some metal surface so that heat from the strip can radiate and dissipate in the case, otherwise the leds are likely to overheat.

Also, typically you have to power the strips every 1-2 meters or so. The wires on the strip are thin enough that they have some resistance, so if the strip is too long by the time power reaches the last leds there's enough resistance on the strip to cause a voltage drop, so the leds towards the end may see 4.5..4.7v instead of 5v.

In extreme cases, the voltage can drop low enough to cause the tiny chips inside the leds to glitch or reset.

 

You'll be better off using dc-dc converters to power each segment separately, converting 12v to 5v.

eBay is full of tiny 1$ converters which can take in 12v and output 5v or some voltage at up to 3A, which should be plenty for 1-2 meters of led strips.

Here's an example:

https://www.ebay.com/itm/DC-DC-3-3V-5V-9V-12V-3A-Adjustable-Buck-Step-Down-Voltage-Regulator-Power-Module/112472497295

or

https://www.ebay.com/itm/DC-DC-Adjustable-Buck-Converter-5V-12V-3A-Voltage-Step-Down-Regulator-Module/302473175701

 

You simply connect two wires to 12v on your ATX power supply (from a molex/hdd connector for example) and you adjust the potentiometer until you get around 5v..5.2v at the output and then connect your led strips at the output.

The led strips should tolerate up to 5.5v so setting the output to around 5.2v should be safe and give the leds all the way to the end of the strip a bump in voltage.