Negative potential on positive plate of capacitor

[jiyer]

What happens if a negative potential is applied to the positive plate of a positive polarity tantalum capacitor? Does this damage the capacitor or affect it in any way?

 

[Jack// ani]

Tantalum capacitors are polarized, so yes, it will damage or might even burst if connected in opposite polarity.

 

[halee awan]

Hello Dears
Look At this thread for Ans
https://www.edaboard.com/threads/56473/

---------- Post added at 05:19 ---------- Previous post was at 05:11 ----------

More over for Best Short Answer is

Polarized fixed capacitor

A polarized ("polar") capacitor is a type of capacitor that have implicit polarity -- it can only be connected one way in a circuit. The positive lead is shown on the schematic (and often on the capacitor) with a little "+" symbol. The negative lead is generally not shown on the schematic, but may be marked on the capacitor with a bar or "-" symbol. Polarized capacitors are generally electrolytics.

Note that you really need to pay attention to correctly hooking a polarized capacitor up (both with respect to polarity, as well as not pushing a capacitor past its rated voltage). If you "push" a polarized capacitor hard enough, it is possible to begin "electrolyzing" the moist electrolyte. Modern electrolytic capacitors usually have a pressure relief vent to prevent catastrophic failure of the aluminum can (but don't bet your eyesight on this).

 

[Orson Cart]

Yes it does damage it, especially if the available current is high, Regards, Orson.

 

[Kral]

This can be very exciting and entertaining (from a distance). Reverse polarity on an electrolytic capacitor, etiher aluminum or tantalum, causes the formation of gas (outgassing). The pressure from the gas can build up to the point where the capacitor can explode. I had an experience with a wet slug tantalum capacitor that was inadvertently installed backwards in a power supply filter. The capacitor exploded, sending the slug through a wall. Don't do it!

 

[jiyer]

Thanks for your helpful replies. If a negative potential cannot be applied to the positive plate of a polarized capacitor - then how come the positive plate of a polarized capacitor can be connected in series with the negative plate of another polarized capacitor? Consider a case where 2 polarized capacitors are in series, with the configuration like this:
--|(---|(---
then how come the negative potential at the negative plate of the first capacitor can be safely applied to the positive plate of the 2nd capacitor?

 

[Orson Cart]

It is the actual voltage polarity across each capacitor in the series string that matters, if you consider the series string of caps closely you will see that charge current always flows into the pos plate when charging and out of the pos plate when discharging - but the pos plate is not allowed to go negative with respect to the neg plate.
Hope this ansers your query, Regards, Orson Cart.

 

[Kral]

You can do this. The result is a capacitor with capacitance equal to C1C2/(C1 + C2). So if the capacitors are of equal capacitance C, then the resultant capacitor will have a capacitance of C/2. However, the resultant capacitor will be a polarized capacitor. Consider the situation where a positive step voltage is applied to the composite capacitor. A surge of current will flow through both capacitors with (conventional) current flowing from the positive plate to the negative plate of both capacitors, You can construct a non-polarized capacitor by connecting the two negative plates together.

 

[jiyer]

The amount of current that flows from the positive to negative plate in a capacitor depends on the initial charge. So, if the positive polarity polarised capacitor C1 is charged to a voltage of 5 V and connected in series with a positive polarity polarised capacitor C2 that has not been charged, as visualized below:

ground ---)|---resistor---)|---ground

or
ground --C1 --resistor --C1--ground

The current flows from right to left. With the voltage drop across the resistor, there is a possibility that the potential between the resistor and C1 can go negative. So is this negative potential at the positive plate of C1 acceptable?

 

[Orson Cart]

You can construct a non-polarized capacitor by connecting the two negative plates together.

Unfortunately this is not quite true, at the very least a diode is needed across each cap to stop it going more than 0.6 volts reverse. Regards, Orson Cart.

---------- Post added at 13:52 ---------- Previous post was at 13:47 ----------

The amount of current that flows from the positive to negative plate in a capacitor depends on the initial charge. So, if the positive polarity polarised capacitor C1 is charged to a voltage of 5 V and connected in series with a positive polarity polarised capacitor C2 that has not been charged, as visualized below:

ground ---)|---resistor---)|---ground

or
ground --C1 --resistor --C2--ground

The current flows from right to left. With the voltage drop across the resistor, there is a possibility that the potential between the resistor and C1 can go negative. So is this negative potential at the positive plate of C1 acceptable?

Any time you try to discharge a polarised cap MORE THAN it has previously been charged will lead to a reverse polarity on the cap, if in the above you charge up C1 and connect with C2 as shown above and then ground the two ends, you will charge C2 backwards i.e. reverse polarity. Regards, Orson Cart.