This hasn't happend to me...yet ... Being relatively new to the hobby, I want to know what happens if a cap explodes. Is there a sound, smell, smoke? Is there a worst case scenario for if one explodes? Thanks!

You may want to have a spare pair of pants ready, just in case...
I remember to 1976 when we were doing a "round robin" (Iowa State, Ohio State, Indiana U., etc.) developing the first ICP-oes instrument where the first ARL 134000's came with Collins transmitters to start and sustain the argon plasma, and about once each week its hiV ceramic caps exploded, sending everyone standing near the ICP to the bathroom for a change of clothing. People who work making tires sometimes take extra pants to work.
Fred

You haven't had a cap blow yet? It's only a matter of time, if you stay in a hobby like ours.

Sound, smell, smoke? Yes. I have seen older-style tubular lytic caps blow out their pressure-equalizing safety vents with a pop like a firecracker, and the vapors came pouring out. I saw a newer-style one blow out its entire positive end, and blow its stuffings all over the chassis. It made more of a thumping sound than a popping sound. Both types of lytics got very hot before they blew. The newer one got hot enough to dissolve the plastic sheath on its aluminum casing.

An old molded-plastic paper cap (like the notorious "bumblebee") can crack like a .22 rifle shot when it blows, only it's not as loud.

When a tantalum cap explodes, it is prone to burn. It can and will burn right through a circuit board below it. A couple or three years ago, one of our members posted a photo of a board he'd pulled out of his computer, a board that suffered a tantalum cap failure. Not a pretty sight.

I endorse Fred's comment about having extra pants handy.

Larry

Yeah, they make a bang, big deal. You get used to it pretty quickly, same as with electric arcs. By the way wirewound resistors can explode too: I was near a 250 watt Dale that let go, blew an end plug right out of the aluminum casing.

In more than 3 decades of letting magic smoke out of electronics, its only happened to me once. I had jerry-rigged an fm data tape recorder, an oscilloscope, a coposite monitor and several other pieces of ac and dc equipment together in a 3/4 ton van for a ground penetrating radar application. Moving down the pavement at 6-8 mph, everything quiet and working beautifully when suddenly it sounded like a shotgun going off right beside me! Lotsa smoke and a little smell. A tubular cap in the fm tape unit had blown! All I could find was very small pieces of paper! Put a new cap in and it still worked! - Don

We used to plug capacitors in the wall socket for fun in college.
Especially fun when you had first year students in the class.

~ Mitch ~

I've had one electrolytic explode. Pretty much sounded like a party popper. I think there might have been a little smoke, but it wasn't a big deal. Startling though.

Bob

I have had 'lytics explode and been injured by the flying pieces of aluminum a couple of times. One almost took out my eye. Wearing my glasses saved my sight on that one, otherwise I be called Patch, or 'Ol one eye. Not a LOL matter.

I do remember getting one radio in to repair and found the main filter cap. had exploded inside.
It was an old WW2 military radio receiver with the screw base aluminum 'lytic casing maybe 3/32 " thick. It had blown completely out of the radio chassis and had flattened out on the top inside the radios' steel case; compressing over 1/4 inch of its top. That must have been one heck of an explosion to cause that much damage to the casing of the cap. I would not have wanted that one to hit me.

Mostly with the new ones they will either vent steam, blow partially or completely off the board, leave their "guts" all over the chassis, or short and burn a hole in the chassis or damage the traces. The "hiss" or "POP" when one goes can be startling when its unexpected.
Mostly I see ones that the DIY customer put in backwards. ("You mean they are supposed to only go in one way?)

You buy a new one.

And if you had installed the exploder, this time pay attention to it's electrical orientation, lol.

If that's joy, I prefer to be glum .

Gimme real Roman candles if I must have the effect.

Larry

I think you've convinced me to wear glasses or safety goggles when working on these.
-John

...of course, if you're working on older equipment with non-vented PC mount electrolytics, you might also get nailed by the flying can if one of them fails and the can blows off...I've seen (actually heard) that happen before; fortunately, the can didn't actually hit anyone, just blew off with a loud POW and wound up spinning around on the floor several feet away...

Back in the late 1970's I was at a Burroughs training class on an early factory-new B4800 mainframe computer when a big "computer grade" power supply cap blew up. It was 3" in diameter and 8" long, several hundred microfarads with 160 volts DC in it, to feed the switch-mode power supplies. It sounded like a bomb went off, and the tech was standing between the cap and the wall in a space not much larger than a phone booth. An engineering change came out for a higher-rated capacitor. The high currents and voltages on exposed bus bars, and the troubleshooting methods would never be allowed today.
Early AC oil capacitors for motors had PCB oil, so in the 1970s they came out with non-PCB oil which was flammable. I saw one of those blow its top and start an oil fire, so the oil capacitors had to be re-designed to break the circuit when the top end with the connectors bulged up from a short.
Don

The very old cans are dangerous. Can spew nasty wet electrolyte when they blow. New ones can still maim if pointed to your unprotected eye when they let go. Most others just go bang and trip the circuit breakers or blow fuses if there are any or burn out resisters.

That's why we urge you to recap your finds before powering up. After all we want to see you back next week.

You will see an X or Y stamped into the end of newer electrolytic caps, so it will open up on those lines while venting, instead of exploding like a grenade.
Don

On the new ones, even if it does not kill you, blind you or make you deaf, you still have to pick all of the little pieces of waxy paper out of the chassis - a lot of little pieces.

This- of course - has never happened to me.

It did happen to me.



L

Experience talking there, Tubenut?