Re: Stupid polarized capacitor tricks



Joel Kolstad wrote:

"Eeyore" <rabbitsfriendsandrelations@xxxxxxxxxxx> wrote

For starters, the 2 foils are separated by a thin piece of paper, so the
foils can't touch.

Well...

1) According to what I've read ,the standard aluminum electrolytic cap really
is just a spiral-wound piece of aluminum

2 pieces of aluminium. One for the anode, one for the cathode.


sitting in a bath of "magic goo"
(initially, it says, a water/glycol mix with an ionic compound such as boric
acid so that it conducts... but these days there's all sort of proprietary
formulas and competition is intense -- hence the whole "leaking caps" on PC
motherboards from a handful of years ago after someone stole another company's
formula and didn't get it quite right), and that sometimes the aluminum oxide
dielectric isn't even formed until after the entire capacitor is constructed,
at which point voltage is applied. It does mention *other* types of
capacitors that use a thin separator (paper, poly-materials, etc), though.

I suggest you 'blow up' an electrolytic. Many of us have done it either
accidentally or even intentionally. The 'goo' that results will always contains
'fluff'. That's the paper separator.

My understanding is that the oxide layer on the anode is so thin that it's very
fragile and easily damaged. Hence the reason for the separator. Without it, I
believe you'd too easily get internal shorts from breaches of the oxide layer,
simply from the 2 foils making mechanical contact.

Where did you read that a paper separator ISN'T used ?


2) The antique radio guys who talk about "reforming" capacitors recommend
using a VARIAC to slowly ramp the voltage up on caps that have been sitting
around awhile, the idea being that without the dielectric is place you really
are looking at something close to a short and applying 120/240V directly will
cause catastrophic failure.

Not really a SHORT actually. Probably just a very high reforming current that can
cause trouble.


3) In my younger years I'd done the cheeseball "trick" of using two
electrolyitcs "back to back" (polarity-wise) to made a crude non-polarized
capacitor,

This is precisely how real world 'non-polarised' electrolytics are made.


and it did work in the sense that the cap with reverse polarity on
it behaved as a small resistor.

Neither has reverse polarity on it. The electrolytic cap also works as a crude
electrolytic rectifier. The consequence of this is that on an AC signal, BOTH
charge up in the correct polarity.


I guess I'll have to try it out -- I suspect John is correct that "write time"
would be measured in seconds,

Megaseconds.

Graham

.

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