[sdiy] Making a NP electrolytic out of two Polarized caps?

[R. D. Davis]

Quothe Ray Wilson, from writings of Sat, Oct 11, 2003 at 08:40:25AM -0600:
> You got it right. Tie the negative ends together (I think this was a Craig
> Anderton tip). When you put caps in series you decrease the capacitance in a

Not sure about it being an Anderton tip, but surely it's been taught,
for many years, as a way of doing things, in basic electronics
classes.  I remember my high-school electronics teacher mentioning
that in the 1970's, and seem to recall reading about it long before
those electronics classes.

> manner similar to the formula for putting resistors in parallel (if you get
> my meaning). In your case you will need to put two 100uF caps in series to
> get 100uF. But this begs the question... 

                                         1
Actually... since the formula is  C = ---------  for two capacitors 
in series...                           1     1
                                      --- + ---
                                      C1    C2

...one would need to use two 200uf capacitors in series; however,
since 200uF isn't a standard value, one may need to use four 100uF
capacitors:

       C1 +  -               C3 -  +
     +-----|(------+      +------)|-----+
  ---+ C2 +  -     +------+  C4 -  +    +-----
     +-----|(------+      +------)|-----+
                                                      1
                                            C = --------------
                                                   1       1
                                                 ----- + -----
                                                 C1+C2   C3+C4


> why don't you just buy some 100uF non-polarized caps?

Oftentimes people might not have those in their spare parts inventory;
it's often a matter of what's easiest, most economical and most
convenient at the time. :-)

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