How to make non-polarized electrolytic cap?

[pftrvlr]

Which of the following is the corect/better way to connect two electrolytic cap to make it non-polarized?

1. neg-neg
2. pos-pos
3. neg-pos

[pikkujöpö]

3. so to end up with two "double" leads

[kevinkr]

Depends on whether or not dc is present..

1 & 2 work fine with most polar caps when no dc is present or it is small relative to the cap voltage rating.

3 only works with new caps - as the caps age and esr increases you will eventually get to the point where the cap exhibits issues with reverse breakdown. There must be absolutely NO dc present. Truthfully I have never seen it done this way in commercial kit.

Frankly it would be better to use a non polar cap in the first place if a suitable value can be procured. Film caps are practical at low values, and much better performers.

Incidentally you should not use anything but a film cap or non polar EL in a speaker cross-over because of the currents involved. Nothing ruins your day quicker than an exploding EL non polar made this way - particularly when it takes that expensive vintage driver with it.

[gootee]

You can connect two identical electrolytics in series, with either both negative leads connected to each other, or, both positive leads connected to each other. Either way should give you a non-polarized cap that has half of the capacitance value of either of the two identical caps.

[pikkujöpö]

Originally posted by kevinkr


3 only works with new caps - as the caps age and esr increases you will eventually get to the point where the cap exhibits issues with reverse breakdown. There must be absolutely NO dc present. Truthfully I have never seen it done this way in commercial kit.

I have seen two polarised electrolytics used for DC blocking,(connected parallel nec-pos). In CD player outputs etc. Is this also bad practise ?

Thanks

[kevinkr]

Hi pikkujöpö,
Yeah, I would consider that to be bad practice, but I am assuming there was no dc voltage present at the output.

Here it is pretty common practice unfortunately to use just a single polar cap in such a situation, and that is not the best practice long term either if you want low distortion..

Any way you look at it, it's a cheap way out - I'd use a modestly priced non polar in all such cases.

Polar and non polar caps suffer dielectric degradation over time with no dc voltage impressed across them - this imo makes them unsuitable in my mind for any high quality application.

[Original Burnedfingers]

Quote:
You can connect two identical electrolytics in series, with either both negative leads connected to each other, or, both positive leads connected to each other. Either way should give you a non-polarized cap that has half of the capacitance value of either of the two identical caps.

Text book correct answer.