WS2811 Issue when too few LEDs

Hardware
1

Hello,

I have a very strange phenomenon with WS2811 12V pixels. The data goes through a TTL RS485 module because I will have some distance, but for these tests, there is no more than 30 cm of cable (whether it’s for power or data).

The phenomenon: With a white color, maximum brightness, if I connect a single arch (42 LEDs), the first 5 LEDs behave randomly. If I add more LEDs at the end, the LEDs in the arch have no issues. If I disconnect the LEDs I added, the arch LEDs remain without issues.
I tried connecting them with a logic level shifter to replace ttl RS485 module but I have the same behavior.

So, it seems that more LEDs are needed to avoid problems, but if you have any idea why this is happening, I would appreciate it.

Thank you.

2

I’d guess at a power connection issue and/or a problem with a strip.

Have you tried swapping the order of the strips to see if it’s dependent on one in particular.
What are you using for a power supply?

3

Yes, I reversed it and it’s identical.
I just did another test. If I use a pack of 50 new WS2811s, and connect the input and output to the power supply, I have the problem on the first few LEDs (about 5). If I use 2 packs together, I have a minor problem with the first one (it goes from white to red white then blue white at random) but if I use 3 packs, I don’t have any problems.

I don’t understand it, because in principle it’s the opposite problem…

4

What are you using for your power supply?

5

A meishile 12v 1200W => https://www.amazon.fr/Alimentation-Convertisseur-dalimentatio-Transformateur-lalimentation/dp/B0845TVXRT/ref=sr_1_1?__mk_fr_FR=ÅMÅŽÕÑ&crid=2X3QEOIOHYGCZ&keywords=meishile+12v+1200w&qid=1701356858&sprefix=meishile+12v+1200w%2Caps%2C93&sr=8-1&ufe=app_do%3Aamzn1.fos.2a4964d5-da8d-479b-a739-01ef3fadb618

And to have 12v to 5v (for esp) => https://www.aliexpress.com/item/1005002197211893.html?spm=a2g0o.order_list.order_list_main.15.30791802FxcwUE

6

I’m moving on.
The LEDs are connected to the power supply at the beginning and at the end. If I disconnect the power supply at the end, I no longer have the problem. I’d like to point out that this cable is divided into 2 cables to supply power to the 2 locations.