I have usually seen it done by just putting two polarized capes in series back
to back.  I seem to remember that you get 1/2 the capacitance of the caps you
started with.

Thomas McGahee wrote:

> Laszlo,
> Yes, you can use non-polarized caps on AC... that is what
> they are for.
>
> I have on occasion built up my own pseudo-non-polarized
> electrolytic capacitors by using two regular polarized
> electrolytic caps and two diodes. This is not "perfect",
> but works reasonably well, especially at higher voltages
> wherfe the diode drop becomes insignificant.
>
>   +---->|----*-----|<------+
>   |          |             |
>   |  -| |+   |   +| |-     |
> --*---| |----*----| |------*--
>       | |         | |
>
> The way it works is simple: for any given polarity
> one diode will be forward biased, and the other
> reverse biased. Thus only one capacitor at a time
> will be active. Both caps need to be the same value.
> For example, if you use two 100 uf 200 VDC caps,
> then you will end up with a cap set rated at
> 100 uf +/- 200 V. Remember that the voltage rating
> is PEAK, *not* RMS!
>
> Fr. Tom McGahee
>
> -----Original Message-----
> From: Cser Laszlo <s7222cse@URAL2.HSZK.BME.HU>
> To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
> Date: Tuesday, February 15, 2000 6:59 AM
> Subject: Non polarised Electrolytic Capacitors
>
> >Hi All,
> >
> >Can someone please give me some URLs on manufacturers or datasheets of non
> >polarised Electrolytic Capacitors? F&T Manufactures them but I couldn't
> find
> >their homepage.
> >I know nothing about these capacitors. Can I use them for AC?
> >
> >Any help would be appreciated.
> >
> >Laszlo Cser
> >