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Bronze Member Username: PanamanianPanama cityPanama Post Number: 14 Registered: Aug-05 | if so how could it happen? and how could it be avoided? |
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Gold Member Username: IlluminatorPost Number: 1326 Registered: Apr-05 | I assume you're talking about one that is put into a charging system. The only way to really get it to explode is if you had it charged and touched terminals. In audio applications apart from that they normally explode from voltage differences. Small difference=top blowing, high difference=whole cap exploding. |
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Gold Member Username: IlluminatorPost Number: 1327 Registered: Apr-05 | http://www.theinquirer.net/?article=5878 This might also be of interest to you. |
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Unregistered guest | The power supply "hardening" capacitors that are used in car audio are electrolytics and have polarity. That is to say they have one positive (+) and one negative(-) connector, always clearly marked as + and -. The negative should always be connected to the ground or chassis of the car. If you connect it the other way around....BOOM! PCB (a suspected carcinogenic fluid) will spray everywhere. A lot of capacitors have an input, output, and ground connector. This type has control circuitry integrated into the top of the cap and is much easier to install. Less chance of error and the control circuit regulates charge up times so you don't get a huge current draw off your alternator when you switch on. Jexx is right about shorting the terminals together. Large value electrolytic caps are meant to store energy, lots of energy, and accidently putting a screwdriver across the connectors releases that energy all at once. Respect an electrolytic cap like you would a car battery. Always insulate the positive connector. I've worked in electronics for about 30 years and I've learned to respect high energy circuits even low voltage ones so double check everything before turning on the juice. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8929 Registered: Dec-03 | easy to blow one up short the terminals after it's fully cahrged, or wire it backward. don't be holding it when you do. it'll take off your hand, or at least it can. |
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Bronze Member Username: PanamanianPanama cityPanama Post Number: 38 Registered: Aug-05 | well i meant just by using it normally. say i'm driving and for "any circunstances" it explode alone. or if my car is parked in the night (or has been parked for 1 week without starting it), could it ever explode just for that? |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8993 Registered: Dec-03 | no, as long as it's not shorted out, it won't explode. when wired properly and protected from anything like a seatbelt falling on the terminals, you're fine. |
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Bronze Member Username: Pricey1985Sydney, NSW Australia Post Number: 16 Registered: Jul-05 | It is very important that the polarity of the capacitor is correct, otherwise the aluminium oxide layer is not made and the component will conduct. The resulting heating effect can result in the capacitor exploding. Another thing about capacitors All capacitors have a maximum working voltage. All insulators have a maximum voltage at which they will retain their insulating properties. If the Maximum working voltage is exceded sparking can occurs over the dielectric, then a hole will be burned in the dielectric and that is the end of the useful life for the capacitor and in the bin it goes. But hook it up right and ull be right. |
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Bronze Member Username: Pricey1985Sydney, NSW Australia Post Number: 17 Registered: Jul-05 | Also i cant see how shorting the capacitor will make it blow up. It will just discharge at a greater rate then normal. Although i may be wrong, if anyone can explane it. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 9032 Registered: Dec-03 | short the capacitor and it'll blow the relief plug at the end rather explosively. try it some time if ya don't believe me. |
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Gold Member Username: CarguyPost Number: 3820 Registered: Nov-04 | If you want to see something explode that's much cheaper than 1F capacitor, try cig lighter. Throw it up in the air and let if fall. Instant explosion. |
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Unregistered guest | Why does a capacitor explode if it is shorted? It depends on if it is fully charged or almost discharged. Charged refers to the voltage and capacitance rating of the cap. Take a 1 Farad capacitor rated at 20 Volts and charged to 13 Volts for example. The energy stored equals 0.5x1Faradx13Voltsx13Volts or 85 Joules. One Joule is equal to 1 Watt per Second of energy so we have 85 Watts per second of energy in that cap. Doesn't seem like much but if we short the cap out it discharges through a very low resistance in a very short time, lets say 0.1 Ohms resistance in 0.01 Seconds. That 85 W/Sec becomes 8500 Watts per 0.01 Second. 8500W through 0.1 Ohms produces 8500W/13V or more than 650 Amps of current for 0.01 Seconds. Enough to vaporize a screwdriver. The cap may survive but it will be a little scorched. Let's hope you weren't holding that screwdriver in your hand. Of course if the cap wasn't charged nothing will happen. A partial charge will of course have less spectacular results. Sorry for the math but it does explain what happens and why. Hooking a cap up backwards to kill it is harder to explain. It involves electron flow through dielectrics and is reaaaaaally boring. Just don't do it. Good car audio components cost too much, go buy a box of cheap lighters. |
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Bronze Member Username: 02gsxrPost Number: 98 Registered: Jul-05 | A capacitor (especially electrolytic) can blow up very easily! If you run too much voltage through them this will happen. That is why you see a lot of capacitors that are rated at 15v, 18v, or even 20v. If a cap is rated at 15V and for whatever reason 18v was supplied - BOOM. This voltage rating you see advertised does not actually mean it supplies more voltage than any other cap, it is basically a safety rating. |
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Bronze Member Username: Pricey1985Sydney, NSW Australia Post Number: 19 Registered: Jul-05 | Yeah i see now, if have to try it one day Thnx |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 9060 Registered: Dec-03 | I skipped the first year EE math because the last time I bothered, all it did was confuse people who most likely never got past albebra anyway. Refering to prior posts, you'll see we were talking about a fully charged capacitor in a car. usually 1Fd, 20V minimum, charged to at least 12VDC |