7 ms·

Usually a cap blows it's top if you either exceed it's voltage rating or it's polarized and the voltage on the pins is the wrong polarity. Outside these two co

by zaarn 7y ago

Usually a cap blows it's top if you either exceed it's voltage rating or it's polarized and the voltage on the pins is the wrong polarity. Outside these two conditions, the only other thing is age, other than that, they tend to not explode.

gonesilent 7y ago
Or it was made with a stolen formula....
zwirbl 7y ago
Tantal capacitors can actually start burning source: https://www.vishay.com/docs/49268/tn0003.pdf https://www.vishay.com/docs/49268/tn0003.pdf other source: at $WORK we are having some problems with igniting tantal caps
- neltnerb 7y ago
  Tantalum capacitors break to form a short while essentially any other option breaks and becomes an open circuit. A short dumps a pile of current across the capacitor. an open circuit usually just means your circuit doesn't work well. Don't use tantalum without a careful plan to deal with this issue... why are you forced to use them instead of a modern electrolytic?
  - zwirbl 7y ago
    I am in the lucky position to develop the firmware for the device / not being the electronics guy The reason is a mismanaged project. Power budget on a CR2032 is tight and initially a supercap with much bigger capacity was planned. The company producing those went out of business and people were forced to somehow get it to market, working. We did, but now those new tantal cap problems arrived.
- jacquesm 7y ago
  That used to be a good source of income. Buy up old analog synths, categorically replace all the caps and they'd usually work again.
magicalhippo 7y ago
I got this great memory from electronics class in high school, we were measuring some circuit which included an electrolytic capacitor, using an oscilloscope. All of a sudden I hear a panicked voice from the back of the class saying "it's growing, it's growing... turn it off... turn it off!" and my other classmate replying "but it _is_ off!" which was immediately followed by a very loud bang. I turn around and see my two class mates looking shocked and confused, covered in fine fur all over their upper bodies, along with the desk. Never got around to understanding just how they managed it, but they most certainly did manage to blow up that capacitor in a spectacular way.
- zaarn 7y ago
  The fun is that capacitors work even when power is off, so if they had several caps together and one was the wrong way round or the power supply was off but not disconnected OR the capacitor was already charged beyond a point of no return, it'll blow. While they look fairly harmless, one should also never forget that capacitors are the most dangerous part of any electric circuit; they don't become safe if power is off and they have no limit to their current other than "what the wire can do", which is usually northwards of "the wire evaporates". I've experienced various caps burn their legs and solderpoints in less than a millisecond without warning once a short was realized. And on top of that, the huge currents running through wires not intended for that will usually cause quite a bit of inductive backlash in nearby components.
  - jacquesm 7y ago
    I've worked with capacitors that were designed to dump their charge in a few us. You really do not want to mess with that stuff without proper precautions, nothing scares me more than a couple of hundred volts power source with an Ri too low to measure. You need to forcibly restrain your cabling or it will jump all over the place during a discharge.
  - mikevp 7y ago
    Heh... Recalling a demonstration by an EE prof way back when. He had the bank of capacitors charging up on his desk, and was writing on the blackboard the equations of how much energy was stored. Hand raised in the back of the room. "Uh, Dr. Miagawa, I think you slipped a decimal point there." Prof looks over his work again, says "Oh, dear" unplugs the charger and backs away. He tapes two meter sticks together with a screwdriver on the end to discharge his little electrobomb. WHAMO, screwdriver vaporizes. I'm pretty much convinced this was not a mistake, it was a "Be really CAREFUL with this stuff!" object lesson.
djrogers 7y ago
So, aside from that, howe was the theatre Mrs Lincoln?
knodi123 7y ago
and then there's the large caps on my AC compressor that tend to go out every few years.
- jacquesm 7y ago
  Those dry out. They're there to help a tri-phase motor run on single phase power and that's massively abusive to the caps. They tend to get hot enough that the electrolyte slowly evaporates in spite of a lot of effort to seal them. If you look carefully you'll find a little 'x' somewhere in the plastic bottom, that's an overpressure relief. If it is distended outward that cap is about to die.
jacquesm 7y ago
You can blow them quite nicely if you manage to create a magnetic field inside the capacitor that exceeds the strength of the beaker it is contained in. That's a lot of bang for your buck, please don't try this at home. The good thing is most capacitors have an internal resistance and inductance high enough that this isn't a problem. But with capacitors that are made for very fast discharge (such as the ones used in old school xenon flash equipment for studios) you may be in for a surprise. Purposefully weakening the container can bring this sort of behavior out at lower levels.
- unlinked_dll 7y ago
  this is definitely something I want to try at home
  - KaiserPro 7y ago
    5x the rated voltage the wrong way across the terminals does a good job.
  - jacquesm 7y ago
    Start small. 1000 uf and work your way up from there. Stay away from anything that looks like it is mechanically reinforced to make the housing stronger for mounting purposes or mechanical stability. Those are bombs. Don't come crying ;)
elihu 7y ago
To be useful in cars, they also need to not explode when physically damaged.
- grecy 7y ago
  You mean like gas tanks?
  - elihu 7y ago
    Capacitors generally release all of their energy all at once if you short them, which is very bad. Gasoline is flammable, but it needs the right fuel air mixture to actually explode. Car fires are relatively common, but as far as I know car explosions are not.

by zaarn 7y ago

gonesilent 7y ago

Or it was made with a stolen formula....

zwirbl 7y ago

Tantal capacitors can actually start burning source: https://www.vishay.com/docs/49268/tn0003.pdf https://www.vishay.com/docs/49268/tn0003.pdf other source: at $WORK we are having some problems with igniting tantal caps

neltnerb 7y ago
Tantalum capacitors break to form a short while essentially any other option breaks and becomes an open circuit. A short dumps a pile of current across the capacitor. an open circuit usually just means your circuit doesn't work well. Don't use tantalum without a careful plan to deal with this issue... why are you forced to use them instead of a modern electrolytic?
- zwirbl 7y ago
  I am in the lucky position to develop the firmware for the device / not being the electronics guy The reason is a mismanaged project. Power budget on a CR2032 is tight and initially a supercap with much bigger capacity was planned. The company producing those went out of business and people were forced to somehow get it to market, working. We did, but now those new tantal cap problems arrived.
jacquesm 7y ago
That used to be a good source of income. Buy up old analog synths, categorically replace all the caps and they'd usually work again.

magicalhippo 7y ago

I got this great memory from electronics class in high school, we were measuring some circuit which included an electrolytic capacitor, using an oscilloscope. All of a sudden I hear a panicked voice from the back of the class saying "it's growing, it's growing... turn it off... turn it off!" and my other classmate replying "but it _is_ off!" which was immediately followed by a very loud bang. I turn around and see my two class mates looking shocked and confused, covered in fine fur all over their upper bodies, along with the desk. Never got around to understanding just how they managed it, but they most certainly did manage to blow up that capacitor in a spectacular way.

zaarn 7y ago
The fun is that capacitors work even when power is off, so if they had several caps together and one was the wrong way round or the power supply was off but not disconnected OR the capacitor was already charged beyond a point of no return, it'll blow. While they look fairly harmless, one should also never forget that capacitors are the most dangerous part of any electric circuit; they don't become safe if power is off and they have no limit to their current other than "what the wire can do", which is usually northwards of "the wire evaporates". I've experienced various caps burn their legs and solderpoints in less than a millisecond without warning once a short was realized. And on top of that, the huge currents running through wires not intended for that will usually cause quite a bit of inductive backlash in nearby components.
- jacquesm 7y ago
  I've worked with capacitors that were designed to dump their charge in a few us. You really do not want to mess with that stuff without proper precautions, nothing scares me more than a couple of hundred volts power source with an Ri too low to measure. You need to forcibly restrain your cabling or it will jump all over the place during a discharge.
- mikevp 7y ago
  Heh... Recalling a demonstration by an EE prof way back when. He had the bank of capacitors charging up on his desk, and was writing on the blackboard the equations of how much energy was stored. Hand raised in the back of the room. "Uh, Dr. Miagawa, I think you slipped a decimal point there." Prof looks over his work again, says "Oh, dear" unplugs the charger and backs away. He tapes two meter sticks together with a screwdriver on the end to discharge his little electrobomb. WHAMO, screwdriver vaporizes. I'm pretty much convinced this was not a mistake, it was a "Be really CAREFUL with this stuff!" object lesson.

djrogers 7y ago

So, aside from that, howe was the theatre Mrs Lincoln?

knodi123 7y ago

and then there's the large caps on my AC compressor that tend to go out every few years.

jacquesm 7y ago
Those dry out. They're there to help a tri-phase motor run on single phase power and that's massively abusive to the caps. They tend to get hot enough that the electrolyte slowly evaporates in spite of a lot of effort to seal them. If you look carefully you'll find a little 'x' somewhere in the plastic bottom, that's an overpressure relief. If it is distended outward that cap is about to die.

jacquesm 7y ago

You can blow them quite nicely if you manage to create a magnetic field inside the capacitor that exceeds the strength of the beaker it is contained in. That's a lot of bang for your buck, please don't try this at home. The good thing is most capacitors have an internal resistance and inductance high enough that this isn't a problem. But with capacitors that are made for very fast discharge (such as the ones used in old school xenon flash equipment for studios) you may be in for a surprise. Purposefully weakening the container can bring this sort of behavior out at lower levels.

unlinked_dll 7y ago
this is definitely something I want to try at home
- KaiserPro 7y ago
  5x the rated voltage the wrong way across the terminals does a good job.
- jacquesm 7y ago
  Start small. 1000 uf and work your way up from there. Stay away from anything that looks like it is mechanically reinforced to make the housing stronger for mounting purposes or mechanical stability. Those are bombs. Don't come crying ;)

elihu 7y ago

To be useful in cars, they also need to not explode when physically damaged.

grecy 7y ago
You mean like gas tanks?
- elihu 7y ago
  Capacitors generally release all of their energy all at once if you short them, which is very bad. Gasoline is flammable, but it needs the right fuel air mixture to actually explode. Car fires are relatively common, but as far as I know car explosions are not.