Double check power setup

[westerwayj]

HI all,

First time setup, reading so much (thanks for the 101 manual also!) and making plan upon plan. Just would like someone to double check my thinking if possible please.
I am using this site to calculate the pixel power injection scheme http://spikerlights.com/calcpower.aspx

I am using a raspberry pi 4B to run FPP connected to SanDevices E682 controller. I have a Mean Well RSP-320-5 (300W 5v) power supply to run 16x 50 node Ray Wu WS2811 pixel strings, I made the rookie error and bought the 24AWG wire ones instead of the 18AWG wire.... Live and learn.

So far as the above calculator tells me (if this calculator website is accurate??) using these pixel strings (50x 5v pixels, 0.3W each, 3" apart, running at 100% on 24AWG wire) the voltage drop is pretty ordinary. My power cable from PSU to pixels is using 3 core 1mm2 (~17AWG) normal home lighting cable which I assumed (before finding this calculator) would be fine.... maybe.

Using these values in the calculator I can run 5m from power to pixels using 17AWG wire so long as I inject power in either end of the pixel string (at pixel 0 and pixel 50). This results in a projected voltage drop of ~7% at pixel 25. Voltage starts at 4.88v either end and drops to 4.64v at pixel 25 in the middle. According to this all pixels are still in the green acceptable range and should (emphasis on the should) be fine.

Is this all sounding OK? Any comments and help is greatly appreciated.

 

[TerryK]

A question: How many power injection cables; 2 to each string, so 32 in total?

Other thoughts so far, The Mean Well is good for 60 Amp and 16 strings of 50 pixels is 800 pixels. I use 0.055 Amp per pixel so that is 44 Amp total. The amp should handle the load all right.
From testing, I've seen that WS2811 5 volt pixels start to dim pretty close to 4.0 volt (which is somewhere fairly close to 5 volt driven at 90%).

 

[westerwayj]

Thanks!

Yeah a power line (+5v and ground) 1mm2 going to each end of each pixel string, first and last pixel. Front end first pixel will be from the controller board using three core 1mm2 for +5v, ground and data (overkill for data but 3 core was cheap). Back end last pixel will be direct from the PSU using 2 core 1mm2 for +5v and ground only. Only the one PSU so common ground across all connections was the advice in the 101 guide to prevent data reference issues.

I was working on no more than 80% load on the PSU to limit overheating issues so I picked the 300W rated supply.

Does the wire sizing and lengths sound OK? I don't want to have cables getting hot etc. Those lengths are my max intention, most likely when setup it will be much shorter distances in reality.

 

[TerryK]

As you mentioned, 1 mm2 is close to 17 AWG (1.04 mm2=17 AWG). My charts have 17 AWG at 16.61 ohm/KM. I can't comment much about the 24 AWG string; I've only tested strings of 18 AWG. Voltage drop towards the center will be greater than 18 AWG of course.

Your are essentially powering 25 pixels per cable so each cable will see the 25 pixels * .055 Amp/pixel. That's 1.375 Amp pretty much at 100% full white. Ohm's Law says E=IR so 1.375 Amp * .01661 (ohm/M) * 5 (the 5 Meters) is 0.11419 Volt drop per single conductor. Because one needs to take into account both the positive and negative voltage drop in the cable, that needs * by 2 which is then 0.2289 Volt. So, Pixel 1 and pixel 50 will see a 5 Volt - 0.2289 Volt = 4.77 Volt. A bit more drop than your 4.88 but I too would say the configuration should light all right.

 

[westerwayj]

Thank you Terry, nearly have all the parts here, just waiting on the E682 now and will give it all a dry run in the garage as suggested in the 101 and videos. The pixel lights wire does look very thin so very dubious about them....