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Old 27th December 2007, 08:20 PM   #1
pftrvlr is offline pftrvlr  United States
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Default How to make non-polarized electrolytic cap?

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
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Old 27th December 2007, 08:31 PM   #2
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3. so to end up with two "double" leads
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Old 27th December 2007, 08:42 PM   #3
kevinkr is offline kevinkr  United States
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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.
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Old 27th December 2007, 08:58 PM   #4
gootee is offline gootee  United States
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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.
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Old 27th December 2007, 09:03 PM   #5
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Quote:
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
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Old 27th December 2007, 09:21 PM   #6
kevinkr is offline kevinkr  United States
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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.
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Old 28th December 2007, 06:41 PM   #7
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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.
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