Small Clone with reversed electrolytic caps works. Why?

KaptenSpark · March 31, 2006, 08:37:39 AM

Today I understood that the marking on electrolytic caps indicated the negative side. When I made my tonepad small clone i just put the markings where the markings were on the pcb drawing. Turns out, the markings in the drawing are + signs. Have I then done it all wrong or all right? It works excellently.

petemoore · March 31, 2006, 09:13:08 AM

Electro's have a - marking near one of the leads, that indicates the negative pole of the capacitor.
Reversing the polarity of a polarized cap may damage it at some point or right away. Caps exposed to Reversed polarity may be 'self healing', when current with correct polarity is used through them.

KaptenSpark · March 31, 2006, 09:32:55 AM

I knew they could blow with reversed polarity, I'm just curious why mine haven't.
So here's a picture, on the drawing the markings are + and in real life they're -. But it works.

George Giblet · March 31, 2006, 10:16:20 AM

I'm surprised the caps across the supplies haven't fried. I'm also surprised your batteries aren't going flat sooner.

For the other positions there's two main cases: When the voltage across the cap is less than about 1 volt the cap will still work properly. The other case is the cap is not working properly, and is leaking current, but that part of the circuit can get away with the lack of couping the cap supposed to provide. For example the output cap might leak DC but you connect this to another device with AC coupling on the input, here the next cap provides the coupling. You may get funny results when connecting to a tube amp which has no AC coupling.

There's also the case where it appears to be working but it actually isn't working as well as it could be

.

KaptenSpark · March 31, 2006, 10:50:22 AM

Some funny mojo going on then. I'll turn them around and see what happens.

Incubus · March 31, 2006, 11:04:47 AM

Well this is a new situation in this forum........

Someone asking why their pedal actually works

TheBishop · March 31, 2006, 12:21:57 PM

When I built my Tweak O, I accidentally reversed the C and E on the 2n3904. It works great so far.

Unbeliever · March 31, 2006, 05:03:31 PM

Quote from: KaptenSpark on March 31, 2006, 09:32:55 AM
I knew they could blow with reversed polarity, I'm just curious why mine haven't.

You haven't put enough reverse-polarity voltage across them. Try 15V or so, that oughta do it.

The caps will 'work' for a while, but eventually will fail, the 'speed' of failure being proportional to the reverse voltage across them. The reverse-voltage de-anodizes the foil in the cap, and it's this foil that blocks current flow. Eventually, this will happen enough so that the current is no longer blocked, and as the electrolyte conducts .... your cap is a cap no longer.

H.Manback · March 31, 2006, 05:09:18 PM

If you can buy them easily (that is, you don't have to order them specifically), I'd just get new caps for it, and put them in the right way. Caps are not exactly expensive, so why risk having a sudden failure of the caps, which could even fry a attached power supply in the worst case.

KaptenSpark · March 31, 2006, 05:25:09 PM

Now I'm convinced. I'll fix it first time tomorrow, don't want it to blow up on the next gig.
Thanks for all the help by the way everybody!

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Small Clone with reversed electrolytic caps works. Why?

George Giblet