the guy Posted January 7, 2010 Posted January 7, 2010 what happens if you keep on charging a capacior? will it just keep on building up charge? or reach a point where it can't charge any longer or explode or what?
vordhosbn Posted January 7, 2010 Posted January 7, 2010 The process is called "breakdown". The cappacitor becomes conductive for small amount of time. http://en.wikipedia.org/wiki/Capacitor#Breakdown_voltage
insane_alien Posted January 7, 2010 Posted January 7, 2010 it will eventually fail, probably by dielectric breakdown where the dielectric layer can no longer seperate the charge and becomes conductive.
the guy Posted January 7, 2010 Author Posted January 7, 2010 oh ok thanks, can a capacitor hold its charge forever? or will it slowly lose it?
insane_alien Posted January 7, 2010 Posted January 7, 2010 in theory, forever. in practice, no they have a leakage rate. capacitors wouldn't be suitible for storing a charge for more than a few weeks. best to use them for short term storage of charge only.
mehran Posted January 21, 2010 Posted January 21, 2010 You sure that if we keep on charging a capacitor, it will breakdown? I think the "dielectric breakdown" will only happen when we put it on a high voltage orbit; i mean if the voltage of the orbit is more than the voltage that the capacitor can take (it is written on it) therefore that capacitor will breakdown; but keeping on charging; i'm not sure!
insane_alien Posted January 21, 2010 Posted January 21, 2010 orbit? what? if the capacitor is charged to a voltage greater than the dielectric breakdown voltage of the dielectric used in the capacitor then it will be destroyed. this is well known.
mehran Posted January 21, 2010 Posted January 21, 2010 orbit? what? if the capacitor is charged to a voltage greater than the dielectric breakdown voltage of the dielectric used in the capacitor then it will be destroyed. this is well known. I meant electric orbit. Yeah, that's obvious, but the question is some thing else! what happens if you keep on charging a capacitor? keeping on is important here; but not the voltage! I hope u get it!
mehran Posted January 21, 2010 Posted January 21, 2010 I think he means circuit. That's right! Thx alot!
the guy Posted February 1, 2011 Author Posted February 1, 2011 when this breakdown happens and the dielectric becomes conductive, once this has happened will the capacitor carry on being able to charge once again or will it be permanently damaged?
TonyMcC Posted February 1, 2011 Posted February 1, 2011 (edited) First of all check the working voltage of the capacitor. If the voltage you are using to charge the capacitor is less than the working voltage you cannot over charge it. It will stop accepting charge when the voltage across the capacitor is the same as the applied voltage. If you use a voltage greater than the working voltage then the dielectric inside the capacitor may well fail. For some capacitors such as electrolytic capacitors this failure may be quite violent (explode). For others the dielectric will probably break down (flash over). In either case the capacitor will probably be ruined. Edited February 1, 2011 by TonyMcC
insane_alien Posted February 1, 2011 Posted February 1, 2011 permanantly damaged usually. tere are a few dielectrics that will return to normal once the capacitor has been discharged. usually gaseous ones like air. most solid and gel dielectrics will become permanantly damaged unless you go to the bother of replacing the dielectric.
Ethereally Luminous Posted February 1, 2011 Posted February 1, 2011 (edited) What if you make a crude capacitor out of a plastic bottle and some foil, maybe ? will the plastic melt after it's been charged too much? Edited February 1, 2011 by Ethereally Luminous
TonyMcC Posted February 1, 2011 Posted February 1, 2011 What if you make a crude capacitor out of a plastic bottle and some foil, maybe ? will the plastic melt after it's been charged too much? Such a capacitor would withstand a very large voltage because of the thickness of the dielectric (and for the same reason have very small capacitance). However if the plastic dielectric failed you would probably find a small hole through it. Because of the thickness of the plastic, unless the foil sputtered and lined the hole, the capacitor would probably recover with air in the hole acting as dielectric.(imo)
insane_alien Posted February 1, 2011 Posted February 1, 2011 well, what would happen is that around the point of breakdown the structure of the plastic molecules will be considerably changed. influencing its conductive properties. you'll find that the conductivity is increased leading to a much faster leak rate of the capacitor and the removal of the dielectric will lead to a lower capacitance. due to the crudeness of the design, it will be quite robust, however its doubtfull that it's be useful in any application.
Ethereally Luminous Posted February 1, 2011 Posted February 1, 2011 Would the change in conducting properties and molecules be permanent? And another idea, something more intricate. What if the capacitor is made with sulphur crystallized in the shape of a jar and the plates being used are good thin silver foil?
Janus Posted February 1, 2011 Posted February 1, 2011 I meant electric orbit. Yeah, that's obvious, but the question is some thing else! what happens if you keep on charging a capacitor? keeping on is important here; but not the voltage! I hope u get it! If I get what you are saying, you are asking what would happen if you didn't disconnect the vloage source from the capacitor, and the voltasge source never exceeds the capacitor rating. In that case we are dealing with the RC time constant. Given a circuit with resistance R and and capacitance C, the time it would take for the capacitor to charge to ~63.2% of the source voltage is equal to R x C. This is called the time constant. It will then take an addtional R x C seconds for the capacitor to charge an addtional ~63.2% of the difference between the present charge and the source voltage. In other words if the time constant were 1 second, and the source voltage was 10v, it would take 1 sec to charge to 6.32V, another second to charge to 8.65 V, and another to charge to 9.5v. etc, etc. Theorectically, the capacitor would continue to charge forever, getting ever closer to the source voltage, but never quite reaching it. In practice, a capacitor is considered fully charged after a certain number of time constant periods. 1
ewmon Posted February 1, 2011 Posted February 1, 2011 what happens if you keep on charging a capacitor? Theoretically, with a constant (less-than-breakdown) voltage applied forever, a capacitor will never completely charge because there's always a difference in potential and, thus, a resulting current (in the same way that an exponential decay never actually reaches zero).
TonyMcC Posted February 1, 2011 Posted February 1, 2011 Theoretically, with a constant (less-than-breakdown) voltage applied forever, a capacitor will never completely charge because there's always a difference in potential and, thus, a resulting current (in the same way that an exponential decay never actually reaches zero). What you say is true. However for all practical purposes the capacitor is usually assumed to be fully charged after 5CR seconds.
infiitesoliduk Posted February 15, 2011 Posted February 15, 2011 What you say is true. However for all practical purposes the capacitor is usually assumed to be fully charged after 5CR seconds. caps are like buckets that don't overfill. Once the plates are covered in electrons thats it.
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now