Author Topic: Capacitors in series and parallel  (Read 1354 times)

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Offline DzAnej

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Capacitors in series and parallel
« on: December 24, 2016, 05:30:07 pm »
Hi,
I've got a straightforward question. Is the end capacitance the same in the both circuits?
 

Online Zero999

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Re: Capacitors in series and parallel
« Reply #1 on: December 24, 2016, 05:47:53 pm »
Yes. Do the maths.
 

Offline DzAnej

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Re: Capacitors in series and parallel
« Reply #2 on: December 24, 2016, 05:51:52 pm »
Yes, i've done it. Is there any difference between the two circuits?
 

Offline MK14

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Re: Capacitors in series and parallel
« Reply #3 on: December 24, 2016, 05:52:07 pm »
There is a simple (common sense) proof.
Half both capacitances (A and B).

By erasing the second chain of 7 series capacitors that A has.

Similarly, remove the lower capacitor, from each of B's 7 capacitor pairs.

This should result in two apparently identical circuits.

Since identical circuits have identical capacitance's (assuming the same capacitor values are used for both). Hence 'YES', the same.

Similarly a theoretical analysis, using capacitor formulas, would also give the answer "'YES'.

So although the answer this gives would be 'YES'.

In practice (real life), one could be nasty and say the answer is 'NO'. Because, in general, no two capacitors, have EXACTLY the same value. Due to small variations in values (due to tolerance etc).

So my final answer is NO, YES because it is over the Christmas period, so I should be nice.
« Last Edit: December 24, 2016, 05:57:29 pm by MK14 »
 

Online wraper

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Re: Capacitors in series and parallel
« Reply #4 on: December 24, 2016, 05:58:04 pm »
If all capacitors have exactly the same value, there is no difference. If values are different, then yes, there is difference.
 

Offline MK14

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Re: Capacitors in series and parallel
« Reply #5 on: December 24, 2016, 06:02:35 pm »
If all capacitors have exactly the same value, there is no difference. If values are different, then yes, there is difference.

Your answer is NOT strictly correct. Because some differences in capacitor values, can cancel out, giving the same final capacitor values.

E.g. 9 uF + 11 uF = 20 uF in parallel
would be the same as 10 uF + 10 uF = 20 uF in parallel
tl;dr
Some DIFFERENT values can still be equivalent.
EDITED, as original post was wrong!
« Last Edit: December 24, 2016, 06:05:23 pm by MK14 »
 

Offline MK14

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Re: Capacitors in series and parallel
« Reply #6 on: December 24, 2016, 06:08:36 pm »
Yes, i've done it. Is there any difference between the two circuits?

The failure modes are potentially different, for starters.

E.g. The effects of a single capacitor going open-circuit, between circuits A and B, in your original OP.
 

Online wraper

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Re: Capacitors in series and parallel
« Reply #7 on: December 24, 2016, 06:30:32 pm »
If all capacitors have exactly the same value, there is no difference. If values are different, then yes, there is difference.

Your answer is NOT strictly correct. Because some differences in capacitor values, can cancel out, giving the same final capacitor values.

E.g. 9 uF + 11 uF = 20 uF in parallel
would be the same as 10 uF + 10 uF = 20 uF in parallel
tl;dr
Some DIFFERENT values can still be equivalent.
EDITED, as original post was wrong!
Only if all of the caps connected in series (as in top circuit) are equal, or values are selected in a special way, it will cancel out. If, all of the capacitors are, say, 1uf, except one which is 1n, it will become obvious that difference between the circuits will be huge.
 

Offline MK14

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Re: Capacitors in series and parallel
« Reply #8 on: December 24, 2016, 06:38:57 pm »
Only if all of the caps connected in series (as in top circuit) are equal, or values are selected in a special way, it will cancel out. If, all of the capacitors are, say, 1uf, except one which is 1n, it will become obvious that difference between the circuits will be huge.
That's true.

I guess the OP should have been clearer, as to the value of C (i.e. each individual capacitor), and confirmed it is the same between A and B.
Also they could have worded the question better. So that component tolerance etc, don't affect the answer.
Or alternatively, I'm too aggressive, at attacking a questions construction and contents.
« Last Edit: December 24, 2016, 06:48:45 pm by MK14 »
 


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