Can I replace a polarized cap with a non-polarized cap?

[64fx]

I found a thread on polarized/non-polarized caps but no specific answer to my question.  Can someone help?

Thanks!

[pazuzu]

i don't think so.

[Philippe]

Are you talking electrolytics? Some electrolytic capacitors are available in NP versions (i.e. the 3.3 uf used in the AMZ mini-booster).

Sizing factors (in relation to available space on the PCB) have a lot to do with whether you can run with a film capacitor or have to opt for an electrolytic type capacitor.

[PRR]

> Can I replace a polarized cap with a non-polarized cap?

The perfect cap has no polarity.

"Film" (paper, mylar, poly) caps are practical non-polar caps in small values. We can generally use them "anywhere".

BUT above 1uFd these become BIG COSTLY parts. This is not an electrical problem, but it may be an economic problem.

If you apply voltage to a (special) pot of salt-water, it forms an "electrolytic" capacitor. A bit leaky, but very compact and cheap in large sizes. Problem is if you reverse the voltage, it leaks like a pot of salt-water again. However there are many uses for a cap where a DC voltage is always in the same direction and a little leakage does no harm.

If you put two electrolytic caps back to back, you get a non-polar electrolytic. This costs more than a uni-polar electro, but less than a large film cap. These are used in motors and loudspeakers. They are generally useful in audio, if leakage is not critical, and if you can find a suitable value, and you don't mind paying significantly more than a plain electro cap.

> Can I replace a polarized cap with a non-polarized cap?

"Yes", BUT.... why was a polar cap specified?

If you find a 0.47uFd polar electrolytic on a plan, and you have a 0.47uFd film cap for audio coupling, it will work. BUT it may be 10 times the size and price. Will it fit the board, the budget? Will that enormous cap body suck buzz and radio from thin air? In many cases, mass-production gear uses lowest-cost electrolytics, and many geeks say the gear sounds better if these are replaced by film cap (and go on to debate polyester versus polycarbonate versus silver loon-oil cap sound).

OTOH, when you find a 1,000uFd 25V power supply cap, the electro is a buck and an inch, a film-cap will be a hundred buck array the size of a breadbox. There are a far number of geeks who build tube power-amps with (20uFd 600V) film-caps in the power supply. I have never seen a high-end transistor amp with 10,000uFd 100V film-caps-- it would cost as much as a car.

[Paul Marossy]

One place where it matters: Don't use non-polarized caps in power filtering applications, it will cause problems. In the audio path, I prefer to use non-polarized for various reasons.

[PRR]

> Don't use non-polarized caps in power filtering applications, it will cause problems.

Non-polar electrolytics ... it's a waste of money and the second unit may rot from lack of bias.

But FILM caps make fine power filters IF you can afford them. All the old W.E. telco gear, and the older Hammonds, used paper-in-oil main filter caps. Worked good and a HIGH-quality paper/oil cap will out-live us all. Many geeks today use huge poly-film filter caps in tube gear, because it is a better cap, and because they can.

In stomp-pedals, the issue is moot. You won't find a high-uFd 10V cap small enough to step on. However the littler coupling caps can go either way.

[Paul Marossy]

Sorry, but I don't agree that you can use film caps in every application, especially in power supplies.

I recently had to fix a batch of guitar pedals that someone else built as they were all non-functional. They used bi-polar electrolytic caps for the power filter caps, and none of the pedals worked until I replaced them with polarized electrolytic caps. And that also applied to the bypass caps on the FETs as they used non-polarized electrolytics for those as well. If it didn't matter, then I shouldn't have had those problems.

[PRR]

Maybe a terminology confusion.

"Film" is often meant to include paper, poly.... the dielectric is a film of like SaranWrap, wax-paper, plastic-bag stuff. You layer metal with plastic film to make a cap. The insulation is very-very good.

Non-polarized electrolytics are still electrolytics, and prone to a large number of troubles. E-caps are Al foil in a pot of salt-water (actually borax or boric acid). A hyper-thin layer of insulating AlOx is formed with electricity. This layer is never as good an insulator as plastic-film, and tends to re-dissolve for various reasons. Plain electros do, of couse, work well in most power and bypass apps. Using a bi-polar electro with a steady DC voltage is an odd waste of money, and I guess I have never run into it.

[Paul Marossy]

OK, I can agree with what you are saying. But my point is that, in my experience, polarization matters in some cases.