Capacitors in series and parallel - Page 1
Forum section: electronics / beginners

author: DzAnej
author_rank: Contributor
timestamp: December 24, 2016, 05:30:07 pm
content: Hi,I've got a straightforward question. Is the end capacitance the same in the both circuits?

author: Zero999
author_rank: Super Contributor
timestamp: December 24, 2016, 05:47:53 pm
content: Yes. Do the maths.

author: DzAnej
author_rank: Contributor
timestamp: December 24, 2016, 05:51:52 pm
content: Yes, i've done it. Is there any difference between the two circuits?

author: MK14
author_rank: Super Contributor
timestamp: December 24, 2016, 05:52:07 pm
content: 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 isNO, YES because it is over the Christmas period, so I should be nice.

author: wraper
author_rank: Unknown
timestamp: December 24, 2016, 05:58:04 pm
content: If all capacitors have exactly the same value, there is no difference. If values are different, then yes, there is difference.

author: MK14
author_rank: Super Contributor
timestamp: December 24, 2016, 06:02:35 pm
content: Quote from: wraper on December 24, 2016, 05:58:04 pmYour 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 parallelwould be the same as 10 uF + 10 uF = 20 uF in paralleltl;drSome DIFFERENT values can still be equivalent.EDITED, as original post was wrong!

author: MK14
author_rank: Super Contributor
timestamp: December 24, 2016, 06:08:36 pm
content: Quote from: DzAnej on December 24, 2016, 05:51:52 pmThe 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.

author: wraper
author_rank: Unknown
timestamp: December 24, 2016, 06:30:32 pm
content: Quote from: MK14 on December 24, 2016, 06:02:35 pmOnly 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.

author: MK14
author_rank: Super Contributor
timestamp: December 24, 2016, 06:38:57 pm
content: Quote from: wraper on December 24, 2016, 06:30:32 pmThat'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.