CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@ganesh p • 18 Sep, 2012
I wonder what happens if a polarised capacitor is connected with the wrong polarity. Will it burst?
@Abhishek Rawal • 18 Sep, 2012 The Capacitor will explode with small puffy smoke & volcano kinda burst.
I have seen it, It's somewhat entertaining.
DO try it, at your home ;-)
@Ramani Aswath • 18 Sep, 2012 The dielectric in such capacitors is an integral oxide film produced by anodizing the anode (aluminium or tantalum foil) at a voltage about 10% higher than the rated voltage of the capacitor. This oxide film is insulating. To ensure that the film is intact and self repairing, an electrolyte is kept in an absorbent medium between the anode and cathode.
The film is destroyed if the voltage is reversed and only a bare metal results. What this means is that the capacitor becomes a short for reverse voltage. The increase in current electrolyses the water in the electrolyte producing oxygen and hydrogen gas which builds up pressure inside the sealed enclosure and explodes as graphically described by TSH above.
(happy Ganesh Chaturthi! Couldn't resist that)
@ganesh p • 19 Sep, 2012
bioramani
The dielectric in such capacitors is an integral oxide film produced by anodizing the anode (aluminium or tantalum foil) at a voltage about 10% higher than the rated voltage of the capacitor. This oxide film is insulating. To ensure that the film is intact and self repairing, an electrolyte is kept in an absorbent medium between the anode and cathode.
The film is destroyed if the voltage is reversed and only a bare metal results. What this means is that the capacitor becomes a short for reverse voltage. The increase in current electrolyses the water in the electrolyte producing oxygen and hydrogen gas which builds up pressure inside the sealed enclosure and explodes as graphically described by TSH above.
(happy Ganesh Chaturthi! Couldn't resist that)
can you give explanation why capacitor short circuits when connected with reverse polarity?
@Abhishek Rawal • 19 Sep, 2012 A reversed voltage changes the dielectric (basically an insulator) into a conductor resulting in short-circuiting the capacitor.
@Ramani Aswath • 19 Sep, 2012
ganesh p
can you give explanation why capacitor short circuits when connected with reverse polarity?
The dielectric is an anodic film. IF polarity is reversed this film disappears due to the reversed electrochemical reaction. Without the dielectric capacitance also disappears. You can have a capacitor made that has the film on both electrodes. This will work either way. However, It will be almost double the size for the same capacitance.
@arunchary • 22 Sep, 2012 one more operation may happens when you considers if capacitor changes its polarity motor get exited in opposite direction , so other situations may considers such that capacitor may get damages ....
@Ramani Aswath • 22 Sep, 2012
arunchary
one more operation may happens when you considers if capacitor changes its polarity motor get exited in opposite direction , so other situations may considers such that capacitor may get damages ....
Are you sure. As far as I am aware of, motor capacitors are the non polarised type. Polarised capacitors are generally the large valued ones used mainly for filtering, wave form smoothening and such.
@arunchary • 23 Sep, 2012 yes sir i have tested in the case of wet-grinders when i placed a capacitor in an opposite polarity, it starts rotating in anticlockwise direction.
@Ramani Aswath • 23 Sep, 2012 I think that we are talking of different things. Polarised capacitors are usually electrolytics. They have a positive and negative terminals. What you are mentioning is that the capacitor is placed on one line or the other of the power supply, not just fixing the capacitor in reverse. In your case the phase shift will be 180 degrees the other way and so the motor reverses. This happens because the rotating magnetic field reverses.
@naveee • 23 Sep, 2012
bioramani
I think that we are talking of different things. Polarised capacitors are usually electrolytics. They have a positive and negative terminals. What you are mentioning is that the capacitor is placed on one line or the other of the power supply, not just fixing the capacitor in reverse. In your case the phase shift will be 180 degrees the other way and so the motor reverses. This happens because the rotating magnetic field reverses.
if polarity changes magnetic field reverses sir ????
@Ramani Aswath • 23 Sep, 2012 The capacitor on a single phase motor shifts the phase on one of the windings so that in effect the motor becomes a two phase motor. However, if the capacitor is shited the motor reverses.
Please read the section on split capacitor motor here:
https://www.allaboutcircuits.com/vol_2/chpt_13/9.html
@arunchary • 25 Sep, 2012 yes exactly....sir
@arunchary • 25 Sep, 2012 yes exactly sir...........
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