Hello guys

I want to ask you something about capacitors! I know very well that if I will join 2 capacitors in series, it will cause the reduction of the capacitance according to the formula:

C=C1*C2/C1+C2 (for 2 capacitors) and 1/C=1/C1+1/C2+1/C3+......+1/Can (for more capacitors)

Especially for the parallel provision* with following formula:

C=C1+C2+C3+......+Cn

Say, we charge each of capacitor provisions (parallel or series) with 12V AC (because the capacitors acts like open circuit if being charged with DC voltage)! What will be the result on that what happen with voltage/current? They will be increased or decreased? Someone said me that if I join 2 capacitors 6800uF in parallel provision and charge them with 12V/1A, then the current will be increased when the voltage is the same, 12V! Is this wrong? If it is not then could I join some capacitors so as to increase the current of a source, that produce 12V/1A AC, to 12V/7A AC? I just asked I have not idea what exactly happens! I just want to make a power supply that produce 12V/7A! What can I do in case if the theory of capacitors is wrong?

*(I don't know if I'm correct with word "provision"! If I said the word with false significance please correct me!)

 

No, energy is ALWAYS conserved, you can't make magic energy by putting more uncharged caps in parallel.

The energy is a cap is 1/2 C V^2

Knowing the initial cap, the final cap, and the initial voltage you can compute the final voltage when you put an uncharged cap across an already charged cap.

 

???????

 

If you charge a 6800μF capacitor with AC it will most likely blow up in your face.
It cannot withstand any excessive heat generated by excessive current from excessive reverse voltage.

Do be careful when you try this.

 

If you charge a 6800μF capacitor with AC it will most likely blow up in your face.
It cannot withstand any excessive heat generated by excessive current from excessive reverse voltage.

Do be careful when you try this.

Ahahahahahahah noo I didn't said I will connect it to the 220 volt! Of course it will blow! I mean if I will charge 2 cap 6800uF/25V in parallel provision with 12V/1A AC the current will be doubled?

 

What do you mean by charge a capacitor with AC?

It will still blow eventually at 12VAC.

 

How the capacitor could blow if it is electrolytic 6800uF and can withstand 25V? And especially on 12V ac? I don't catch you!

 

Oops, I missed that was AC not DC.

Do not try this at home. An electrolytic will explode if you put 12 VAC across it. They are designed for DC only.

 

The term "charging a capacitor" does not have meaning with AC as there is always current flowing through a capacitor when there is an AC voltage across it. The current through a capacitor when connected to DC starts of off at a high value (Limited by the source impedance.) and decays to zero when the voltage across the capacitor reaches the DC voltage. The reactance (Similar to but not the same as resistance) of a capacitor depends on the value of the capacitor AND the frequency of the AC. The reactance is 1/(2 x Pi x F x C) The current though two capacitors in parallel with the same voltage and frequency across them will increase. (The sum of the currents through each capacitor.)

Les.

 

Oops, I missed that was AC not DC.

Do not try this at home. An electrolytic will explode if you put 12 VAC across it. They are designed for DC only.

DC? But the capacitor doesn't work on DC voltage/current! It works only on AC! Sorry for that but in my school I learned that if you join a capacitor to DC the current will pass across the capacitor until the capacitor will be fully charged! After that the current will be 0! But if you join the cap on AC the cap will charge and discharge with the result the current will pass across the capacitor! Am I right on this? If I know well the cap can blow if you will connect it reverse! Right?

 

I didn't said that I will do any experiment! I just ask so as to know about everything, because if I will do any explosion I will find answers why it is happen with no knowledge, then spend many moneys for capacitors, and i don't want that! That why I ask!

 

Capacitors work with AC and they work with DC.

I've seen so many incorrect things said on the board and others concerning capacitors that stating what they really do has become an act as foolish as trying to fix the internet.

 

Can you tell us what level school are you in that teaches about capacitors?
Do you know what is capacitive reactance?
Do you know what is impedance?

Read what LesJones said in post #9.
You don't "charge" capacitors with AC.
Capacitors behave a certain way when DC is applied. They behave in another way when AC is applied. You can calculate the current in either case.
Do you know how to calculate current?

 

Yes but on the DC voltage/current the cap acts like an open switch which opens slowly until the cap is fully charged! The capacitor cannot discharge on a DC current! It can only be charged! But if I want to discharge it I have to open the switch until all this current will be gone and then close the switch again and all this process again and again!

 

For sure you can discharge a capacitor on DC.

How long does it take a capacitor to charge?
How long does it take a capacitor to discharge?

 

Can you tell us what level school are you in that teaches about capacitors?
Do you know what is capacitive reactance?
Do you know what is impedance?

Read what LesJones said in post #9.
You don't "charge" capacitors with AC.
Capacitors behave a certain way when DC is applied. They behave in another way when AC is applied. You can calculate the current in either case.
Do you know how to calculate current?

Um I don't understand English but I will translate them all! I'm in technical lyceum in Greece! I know what is the impedance what is the reactance! But some explanation of each of your following will not spoil me ! I know one thing! I don't know anything! (I don't know if I said it right)

 

Um I don't understand English but I will translate them all! I'm in technical lyceum in Greece! I know what is the impedance what is the reactance! But some explanation of each of your following will not spoil me ! I know one thing! I don't know anything! (I don't know if I said it right)

Exactly! You said it right.
You need to read up more about capacitors.

Here is one place to start:

https://www.allaboutcircuits.com/textbook/direct-current/chpt-13/electric-fields-capacitance/

 

For sure you can discharge a capacitor on DC.

How long does it take a capacitor to charge?
How long does it take a capacitor to discharge?

That's depending of its capacity

 

Can you tell us what level school are you in that teaches about capacitors?
Do you know what is capacitive reactance?
Do you know what is impedance?

Read what LesJones said in post #9.
You don't "charge" capacitors with AC.
Capacitors behave a certain way when DC is applied. They behave in another way when AC is applied. You can calculate the current in either case.
Do you know how to calculate current?

I have to say no! I don't know how to calculate the current! (I still remember the piece of paper where I wrote what I should to be careful so as to don't harm nobody!!! So I will let someone who knows better than me and will learn!! )

 

Oooh I forgot to explain why I ask this question about capacitors! I planing to make a power supply that increase the 12V/1A to 12V/7A! Someone in my class said me that if I will put many capacitors in parallel position I can increase the capacity and the current keeping the voltage constant! Is that true?

So good night guys and thank you for all! I hope I will get the answer !