Saw a cap vent today

[mmartell]

Had the back removed from an Olevia lcd today which is going black after a few seconds and whoa, as I was looking around to the front of the set a steam trail caught my eye. Spewed a good four feet or so just like a steam whistle without the whistle lol. Actually, can't remember if there was any sound involved ? Pretty cool though.

Cap was a 1000uf 35v in the audio section of the mainboard. Have yet to replace it.

[tom66]

Re: Saw a cap vent today

I had a 450V capacitor vent on me due to a failed PFC circuit dumping 600V+ into it. That was impressive, and the room stank for the rest of the day.

[ReeceyBurger123]

Re: Saw a cap vent today

I recapped a vrm on an asus motherboard that had the capacitor polarity markings backwards (they had the stripe as positive and empty as negative, were as normally its the other way around) and because I wasnt observant enough I installed the capacitors the "conventional" way and as soon as I fired the motherboard on my test bench a heard a slight hissing and a small amount of steam so I instantly shut of the board and realised my mistake and the fact that ive killed 3 nice rubycons and now have to spend more time on this peice of junk. WHY ASUS ?

[ReeceyBurger123]

Re: Saw a cap vent today

That was when I was 13 yo and only knew the normal markings of capacitors.

[electricboyo]

Re: Saw a cap vent today

After 40+ years of electronics work, I still must confess to occasionally mounting an electrolytic capacitor with reversed polarity! Doing this certainly does cause them to vent!

-EB

[Shinju]

Re: Saw a cap vent today

Also makes you jump when they pop! Only done that once on a Rail cap on a car amp!

BOOM, shredded paper everywhere!

[electricboyo]

Re: Saw a cap vent today

Electrolytics aren't the only type that can pop.

I restore antique radios. Old radios contain axial "paper and foil" capacitors. Typically these are in molded black plastic tubes with colored marking bands ("bumblebee" caps) or are in cardboard tubes covered with wax. After 50 or 60 years, the paper dielectric breaks down and these capacitors become leaky. They act as if there is a resistor in parallel with the capacitance.

One capacitor, usually 0.01uF or 0.05uF is connected directly across the incoming 120V AC power. This is called the "line cap." Often this cap is powered even when the radio's power switch is off.

One time, while I was hunched over the radio chassis positioning my test probes, a line cap exploded loudly, blowing shreds of paper and foil all over my face. Good thing I was wearing glasses! After that I always change these line caps before powering up old radios. When such a capacitor becomes leaky AND has 120V AC applied to it, it can get very hot very fast!

Today, there are "safety rated" line caps (type X1) that are guaranteed "not to pop!"

-EB

[goontron]

Re: Saw a cap vent today

Electrolytics aren't the only type that can pop.

I restore antique radios. Old radios contain axial "paper and foil" capacitors. Typically these are in molded black plastic tubes with colored marking bands ("bumblebee" caps) or are in cardboard tubes covered with wax. After 50 or 60 years, the paper dielectric breaks down and these capacitors become leaky. They act as if there is a resistor in parallel with the capacitance.

One capacitor, usually 0.01uF or 0.05uF is connected directly across the incoming 120V AC power. This is called the "line cap." Often this cap is powered even when the radio's power switch is off.

One time, while I was hunched over the radio chassis positioning my test probes, a line cap exploded loudly, blowing shreds of paper and foil all over my face. Good thing I was wearing glasses! After that I always change these line caps before powering up old radios. When such a capacitor becomes leaky AND has 120V AC applied to it, it can get very hot very fast!

Today, there are "safety rated" line caps (type X1) that are guaranteed "not to pop!"

-EB

HA! you should see a black beauty cap pop, that will embed into your skin, or the wood cabinet, or chip the bakelite

[electricboyo]

Re: Saw a cap vent today

Black Beauty caps.

Guitar players will pay an arm and a leg for these things. They use them inside the guitar body as a tone control cap. I guess that's OK since there's no DC voltage and the AC voltage is only millivolts!

So should we all start selling the old Black Beauty and "bumblebee" caps on ebay that we take out when we are recapping? I've probably thrown away a couple hundred of them! Silly me!

EB