Introduction: Custom Capacitor Values

Sometimes schematics call for an uncommon capacitor value.  Instead of ordering a new capacitor online, consider creating a custom capacitor by combining multiple capacitors together in parallel.

Capacitance adds in parallel, this means that the total capacitance of a set of capacitors in parallel equals the sum of all the contributing capacitors.  The images above show how to wire capacitors in parallel.  When two capacitors, C1 and C2 are wired in parallel, their combined capacitance equals C1 + C2.  This principle applies to more than two capacitors, three capacitors in parallel, C1 C2 and C3, have a combined capacitance of C1 + C2 + C3.

As an example I wired together a 0.1uF and a 0.01uF capacitor in parallel on a breadboard in fig 1, the total capcitance between the yellow wires is 0.01 + 0.1 = 0.11uF.

Comments

author
whiskeysausage (author)2013-06-16

can you 'trickle' charge a capacitor?

I understand that a capacitor must be charge by the same voltage that the capacitor can hold before the plates reject incoming. I.e. - a 9v battery can charge a capacitor to 9volts. No more no less.

There is though, no mention of amperage. Can you trickle charge a capacitor at 9volts, but 0.001amps, and over time, achieve a fully charged capacitor capable of discharging 9v worth of energy at one amp?

Or is there a pre-determined 'amp' rating that capacitors must be charged at?

Thanks.

author
ouss76 (author)2012-07-03

you forget to add that when wired in parallel if your 2 caps are rated for lets say 25V the resulted cap will also be 25V.

if you wire your capacitors in serie, then you have:
Ctotal= (C1 x C2 x C3) / (C1 + C2 + C3)
if they are rated for 25V your equivalent capacitor will be 75V

author
noobaholic (author)2012-06-27

If you're only concerned about low frequency operation, this is a good hack. However, each of those capacitors has a different frequency response that depends on its own capacitance. At higher frequencies, your larger caps will have a lower impedance than your smaller caps. This could lead to some nasty surprises (or it could be designed that way!), but for most applications it shouldn't affect it terribly.

author
RoboTable (author)2012-06-27

Smart!

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