Series Capacitors

[Kipper4]

Please explain how this works and how to calculate the new value when daisy chaining capacitors.
In my newest trial i've ended up with two small caps in series and I'm sure when i started a friend told me that this works differantly to resistors in series but i cant for the life of me remeber how. and when i've seen this mentioned using caps in series and parallel the calculus didnt make sense to me. Mainly because i cant remember how he said to do it.
Please refresh this dimwit mind.
Thanks
Rich

[aron]

http://www.engineeringtoolbox.com/capacitors-parallel-series-d_1388.html

Check this page.

[Bill Mountain]

It's opposite to resistors.

Here's a handy calculator:

http://www.electronics2000.co.uk/calc/series-parallel-capacitor-calculator.php

In short capacitors in series are paralleled and parallel capacitors are added together.

[Kipper4]

Ok thanks guys

so if i have it correct in series

C  total =              1 /C1 + 1/C2 
         
in my case

1/100nf   +  1/20nf = 0.06
i guess 6 NF

yet when i use the calculator i get 16.6 or sum such
what am i doing wrong?

[Mark Hammer]

You have to take the reciprocal of the sum.

so 1/100nf + 1/47nf = .01 + .0213 = .0313

take the reciprocal of that ( 1/.0313) and you get 31.97nf

This comes in very handy when you want a 3-position toggle to provide three different capacitances, say for different BBD clock ranges or for tone rolloffs.

For example, the Small Clone uses a 150pf cap top set the BBD clock/delay range.  Put a 220pf cap in series with the 150pf, and wire up a 3-position toggle so that the common/middle lug of the switch goes to the junction of the two caps, and each of the remaining switch lugs goes to the "far end" of each cap.  In one side position, the 220pf cap with be bridged/shorted, yielding 150pf.  In the other side position, the 150pf will be bridged/shorted, yielding 220pf.  In the middle position, the two caps will be in series, yielding 89pf.  Short, medium, long delay range, just like that.

[bluebunny]

This is what your formula should have been:

C  total =          1 / (    1/C1 + 1/C2    )

So 1/0.06 is indeed 16.67.

[Kipper4]

i get it now
thanks guys
i needed to divide the one by the sum again
it makes sense now

[CodeMonk]

For anyone interested, I have a bunch of calculator web pages I saved to my hard drive.
I zipped them up and put them on dropbox for anyone who may be interested...
Its a 6+ Meg file, HTML and images etc.
The pages are from various sites.

https://dl.dropboxusercontent.com/u/70950813/HTML_BASED_HELP.zip

[Kipper4]

Thanks Monk

[samhay]

Another trick with series capacitors is that if you use two polarised caps back-to-back (anode-to-anode or cathode-to-cathode) they become non-polarised.
Handy if e.g. you are using a synth design that uses 10u non-polarised caps. You can sub two 22u electrolytics back-to-back to give you 11u non-polarised.

[Kipper4]

Thanks for the tip Sam. That's just what I needed to know I have a project requiring a 47 if  non polarised and I have an abundance of 100 uf polarised so with this knowledge I can now do the project. Thanks

[duck_arse]

somewhere, I don't know where, (maybe it was rg somewhere) someone said electros shouldn't be put back-to-back without referencing the inner connection, like with 1M to ground or similar. I don't know if this is such a big deal, probably not. opamp oscillators still oscillate with them in the feedback loop un-ground referenced.

I had been wondering, it's always something, about electos in a phase shift osc, and which way they would go, what with the middle one being grounded at both end. then I saw a circuit with one of the two resistive legs taken to V+, which nicely solves the polarity problem.

[samhay]

somewhere, I don't know where, (maybe it was rg somewhere) someone said electros shouldn't be put back-to-back without referencing the inner connection, like with 1M to ground or similar. I don't know if this is such a big deal, probably not. opamp oscillators still oscillate with them in the feedback loop un-ground referenced.

I had been wondering, it's always something, about electos in a phase shift osc, and which way they would go, what with the middle one being grounded at both end. then I saw a circuit with one of the two resistive legs taken to V+, which nicely solves the polarity problem.

I have been told that too, but I haven't blown any up yet (not that I do this a lot).

Edit: And to follow up a PM from kipper. There seems to be a bit of confusion about back-to-back electrolytic caps, so I double checked. It seems to be ok to use them as-is - see e.g. the bottom of the first page of this: http://electrochem.cwru.edu/encycl/misc/c04-appguide.pdf

[Kipper4]

Thanks for all the help guys when i get to cross this project (a direct record/Headphones board for my noisy cricket) off the list i'll give it a go.

[duck_arse]

anyone reading this thread should also shuffle over to:

http://www.diystompboxes.com/smfforum/index.php?topic=102952.msg915013#msg915013

rg came along and answered all our questions.