Safety valve in capacitors - Page 1
Forum section: electronics / beginners

author: babi
author_rank: Contributor
timestamp: January 30, 2013, 06:19:05 pm
content: In this video I have investigated the effect of safety valve in electrolytic capacitors at the time of explosion.You'll see that higher capacity ones without safety valve are really dangerous.

author: Neilm
author_rank: Super Contributor
timestamp: January 30, 2013, 06:52:38 pm
content: I think this from Warcraft 2 is applicable

author: mariush
author_rank: Super Contributor
timestamp: January 30, 2013, 09:30:37 pm
content: And what's the video supposed to prove?That if you push 100v through a 16v it explodes?Those vents are there to allow the case to expand in time and allow the gasses to release slowly... which are caused due to temporary excesses of voltage, overheating, the keyword here being TEMPORARYIf the capacitor is under constant overvoltage or excess current, the capacitor will continue to release gas and increase the pressure faster than the speed the aluminum can bend/deform.Repeat the process by using some pwm to send some voltage every few seconds for a few ms and see if the same effect happens.

author: babi
author_rank: Contributor
timestamp: January 31, 2013, 03:00:16 am
content: Quote from: mariush on January 30, 2013, 09:30:37 pmAnd how did you assume that I am feeding 100v to the caps?I do know that the applied voltage must be temporary, but according to the datasheet I had, the safety valve should work when applying twice the rated voltage at a limited current of 2A to the capacitor.And I did exactly this. I have fed 30v (2A limited) to a 16v cap and you see that in two cases, the vent didn't work and the caps blew up.

author: mariush
author_rank: Super Contributor
timestamp: January 31, 2013, 04:40:40 am
content: "In this video I have investigated the effect of safety valve in electrolytic capacitors at the time of explosion."The point I was trying to make is that it wasn't an "investigation" - you just put 30v at 2A through them. Of course some will pop instantly, some will crack and leak, if you take 100 capacitors from the same badge you won't find the same answer.An investigation involves several capacitors of same series, various methods of testing like continuous voltage, pulsed voltage (over the rating), negative voltage, effect of temperature on the speed of leaking etcYou just took several random capacitors and put voltage on them. Yeah, that's really conclusive, way to do determinations. It's no more different than any youtube video out there with capacitors blowing up.

author: babi
author_rank: Contributor
timestamp: January 31, 2013, 05:28:58 am
content: I think you don't understand what I said.I said that the datasheet says the vent works under their test conditions which was 32v at 2A. So, if I repeat the experiment, it should work too.But we see it didn't.I don't have to try this for 100 more caps.If you are at the quality control of a capacitor manufacturer and you notice that a single sampled cap doesn't meet your declared specs, will you try 100 more caps to prove that your specs are right or you'll improve your manufacturing process?I'm not a native English speaker, so I may have misused the word "investigation", if that's the problem.

author: BravoV
author_rank: Super Contributor
timestamp: January 31, 2013, 05:44:11 am
content: I'm not sure after watching that video, looks like you're not aware at all that those caps are polarized and "must" be connected properly.Looking at the inconsistencies of the way you attached the power cables polarities at different cap's pins, let alone higher voltage, even at lower than cap's rated voltage, they will explode or vent if connected wrongly.Attached below screen shot example at just one of many other mistakes you've made.

author: babi
author_rank: Contributor
timestamp: January 31, 2013, 06:08:46 am
content: Quote from: BravoV on January 31, 2013, 05:44:11 amI didn't want to show that the capacitor would explode! Everyone knows that electrolytic caps will blow up if connected to reverse polarity even much lower that their rated voltage.I just wanted to show that under company's test conditions (reverse polarity twice the rated voltage with limited current), the air vent may not work as supposed to.If the air vent doesn't work properly, according to my observation and calculations, the cap may explode and the metallic part could reach the speed of 5m/s which would be very dangerous.