Non-polar electrolytic caps

I just had occasion to replace a bad non-polarized aluminum
electrolytic capacitor. This gave me a chance to tear it open just to
see how it was made.

My first thought was that perhaps they just packed 2 caps in series
inside a single package. That was wrong.

My second thought was that they could be really clever and roll THREE
(or actually 4) foils together, instead of the usual 2. Done this way
they could make an NP cap by just oxidizing both foils which were
connected to the leads and leaving the interleaved foils floating.
This was also wrong.

The cap I took apart was constructed exactly the same as any other
electrolytic cap: just 2 foils. I assume that in this case, they
simply oxidized BOTH foil strips.

I replaced the NP cap with 2 normal alum electros (each with twice the
desired capacitance) in series (nose to nose) and put a diode around
each cap to force any voltage drop to occur only across the proper
cap. This seems to work perfectly.

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