ANOTHER pixel fire!

[Santacarl]

I should also point out that for the 5V and the GS8208 pixels, there is a resistor in series with the capacitor. So, if the capacitor fails the resistor limits the current and you won't have a catastrophic failure.

That's interesting. With the resistor in line it probably wouldn't get hot enough to ignite.... It's scary to think how many of those 'fire' pixels are still out there. It's a wonder there hasn't been a bad event somewhere along the way.

 

[steve123]

It's a wonder there hasn't been a bad event somewhere along the way.

There have been a few where the fire department has been called to put out a house fire. No houses completely destroyed as far as I am aware but there have been some serious incidents.

 

[Utimgr]

I've never seen a MLCC catch fire, typically they fail open. That being said, they can burn open with too much voltage applied to them. Tantalum caps can and do catch on fire, I've witnessed that first hand.

 

[steve123]

I've never seen a MLCC catch fire, typically they fail open. That being said, they can burn open with too much voltage applied to them. Tantalum caps can and do catch on fire, I've witnessed that first hand.

The primary failure mode is to fail short. There is an overwhelming amount of evidence for this. Here is a summary:

What happens when a ceramic bypass or decoupling capacitor goes bad?

What happens when a ceramic bypass capacitor fails? I am picking out parts and is wondering is it worth the extra few cents for rated capacitors? Since generally most IC can function without a bypa...

electronics.stackexchange.com

Here are few links to industry, academic and conference proceedings discussing MLCC failures:

https://escies.org/download/webDocumentFile?id=64630#:~:text=Multi%2DLayer%20Ceramic%20Capacitors%20(MLCCs,during%20the%20PCB%20manufacturing%20process.

Failure Analysis of Capacitors and Inductors

General construction of Tantalum, Aluminum electrolytic, Multi-layer Ceramics, Film, and Super capacitors and Common Mode Choke and Surface Mount inductors are explained.

www.kemet.com

https://mdpi-res.com/d_attachment/electronics/electronics-12-01297/article_deploy/electronics-12-01297.pdf?version=1678277129

https://www.kyocera-avx.com/docs/techinfo/CeramicCapacitors/barium.pdf

 

[steve123]

With the resistor in line it probably wouldn't get hot enough to ignite.

Exactly. The resistor limits the amount of power that can be dissipated by the failed capacitor so that it cannot reach the ignition temperature of the epoxy or the pcb material. There is still one failure mode that prevents the 5V pixels from being intrinsically safe and that is the ws2811 itself. If one or more of the ws2811 LED connections fails short then it could cause a lot of power dissipation by the ws2811 package. The 5V pixels operate the ws2811 in its Safe Operating Area so it is at its most reliable operating conditions. The 12V resistor pixels operate the ws2811 at the edge of the Absolute Maximum which reduces reliability. The simple way make them all intrinsically safe would be to manufacture the pixels with a fuse. Fuses are considered infallible and would prevent catastrophic pixel failure.

 

[ErnieHorning]

What happens when a ceramic bypass or decoupling capacitor goes bad?

Interesting read. In the 25 years of environmental HALT (Highly Accelerated Life Testing), (temperature, ESD & vibration), I never, even once, had a ceramic capacitor short or blow up. -148°F (-100°C) - 425°F (218°C) temperatures, 25,000 votes ESD, & 50 G's of vibration. Electrolytic and tantalum, absolutely.