Puff the magic capacitor (is dried electrolytic fluid conductive?)

[thelonious]

I'm kind of surprised I haven't done this more often with all the poking and prodding I end up doing to my boards, but today I exploded an electrolytic cap and just about gave myself a heart attack. It went 'POP' in a roiling cloud of magic smoke. I must have shorted the wrong thing with my test probe and not noticed until it was too late. Anyway, it left behind some shiny electrolytic liquid on the surface of my board. After removing the cap, I was getting weird resistance readings and then realized---duh, electrolyte is more or less conductive depending on its concentration, right? Sure enough, I measured the resistance of the shiny spot and got ~3M. I took an air compressor to it until it dried out, and re-measured it: ~35M. I had painted the board and couldn't use acetone on it, so I used white vinegar and a Q-tip to remove as much as possible and then dried it out again. After that, it was out of the range of my meter. Moral of the story: if you explode a cap, clean it up!

The question part of this: Would it have been non-conductive if I had let it dry completely?

[PRR]

> Would it have been non-conductive if I had let it dry completely?

Dunno.

A simple water-rinse should have been ample. DRY WELL.

Also: the "magic spice" is Boric Acid or similar. I'm not sure another acid (vinegar) is the right rinse.

Obviously needs experimentation. Get Video of the explosion phase. (Rinse is too dull to waste film on.)

[thelonious]

Obviously needs experimentation. Get Video of the explosion phase. (Rinse is too dull to waste film on.)

The smoke was pretty epic (upside-down mushroom cloud-ish). Video would have required audio editing, though. Scared the ___ out me.

[Quackzed]

i popped a biggun once, a 1000uf 100v the size of a D battery... it was pretty scary... BZZZZZZZZZZZZZZZZZZ sounded like a giant mosquito getting zapped by a giant bug zapper... person zapper? whew that was scary!

[PRR]

I popped a soup-can cap. While the audience was coming in. Mushroom cloud.

Autopsy showed my "117V" outlet was running closer to 200V. And that a coffee-maker in the adjacent office wouldn't heat. Experienced US sparkys will recognize the problem.

[thelonious]

Weird neutral connection somewhere...?

[duck_arse]

I always thort the wet goo, smoke and noise less of a problem, the huge amount of atomised bits of foil and paper spread all over more so.

[edit :] also, puff, the magic dragon was my very fave as a little kid, followed by take me for a ride in your car car, which had no dragons or capacitors in.

[R.G.]

Back when I was a wet-behind-the-ears engineerling, I specified the position of the rectifier diodes on a power supply board backwards. This particular power supply had a cluster of 3" diameter, 8" tall filter caps (there was some significant current in there...) and the lab tech built it *exactly* as I'd drawn it up.

The rectifier diodes literally exploded. We found pieces of diode across the room. The caps sprayed goo all over the ceiling. Apparently there wasn't enough energy to convert to smoke, but the tech never would fire up anything of my design again.

I then submitted a patent disclosure for an early version of the steam engine...   

[PRR]

> Weird neutral connection somewhere...?

OK, more clues.

The lounge and office had been in use for several years, no problem until that time.

This building was done in the early 1970s, when we were throwing all our copper into a swamp in southeast Asia.

The Aluminum neutral-wire was oxidizing in the clamp at the fusebox. That day it became 100% Aluminum Oxide, a great insulator.

The attending sparky knew exactly what to do because all the more-used circuits in the building had already failed. This less-used corner of the building had escaped attention.

[armdnrdy]

The condition you are referring to loves to eat PC power supplies! 

[anotherjim]

There is some gunk that is sold to neutralize and identify battery acid leaks. IRC it changes colour in contact with acid. Maybe that dabbed around with a Q-tip is good to treat electrolyte? Can't remember the trade name for it, but this looks similar...
http://www.batterystuff.com/battery-products/miscellaneous-accessories/BC13oz.html

[samhay]

> Would it have been non-conductive if I had let it dry completely?

Probably not unless it formed a rather unusual crystal - you need to have freely(ish) diffusing charge carriers (ions) in an electrolyte solution for it to be reasonably conductive. If there is no more liquid left, there isn't much scope for diffusion to happen.

[R.G.]

> Would it have been non-conductive if I had let it dry completely?
Probably not unless it formed a rather unusual crystal - you need to have freely(ish) diffusing charge carriers (ions) in an electrolyte solution for it to be reasonably conductive. If there is no more liquid left, there isn't much scope for diffusion to happen.

Problem is, the dry stuff is almost certainly hygroscopic to some degree, maybe A LOT, and unless the air around it is dessicated, it will make a great humidity sensor, with its conductivity going up and down with the local humidity.

A particularly ugly situation would come up if the slighty-damp stuff also liked the chemical composition of the board or solder mask, and slowly crept in a thin film across it.

Cleaning PCBs is not all that tough - deionized water spray followed by alcohol flush and forced-air dry will do it fine. Just don't leave contaminated water in contact with circuits either under power or for long periods. Our local grocery store just installed a "Dry Box", intended to restore wet cell phones by some magic - which I suspect is an alcohol flush and dry.

[PRR]

> you need to have freely(ish) diffusing charge carriers (ions) in an electrolyte solution for it to be reasonably conductive

True, but-- the gunk in modern electrolytics is "dry" yet conducts well enough to pass the normal capacitor current and well enough for the blow-up current.

It isn't desert-dry, but there is no free water, a dry paste.

I don't know if fully-dry it would quit conducting. But as R.G. suggests, many active powders will attract damp from the air.

More Experimentation!!
________________________

Larry> The condition you are referring to loves to eat PC power supplies!

Yeahbut... this was a decade before "PC"s became common. I think there was one card-based memory typewriter on campus which could hold a several page document. (Actually I recall a mag-tape band, and probably from R.G.'s ex.)

The caferteria kitchen was upstairs and you can imagine how many costly cooking devices could blow-up with 190V on a "117V" line. (Against this, the largest swill-vats were probably 230V heaters on 208-Y power.)

[samhay]

> the gunk in modern electrolytics is "dry" ... It isn't desert-dry, but there is no free water, a dry paste.

I have to admit that I haven't opened one up for a long time, but thought most of the aluminum caps - at least the cheap ones that we tend to use - still used a paste, which is still wet enough to allow molecular diffusion. A quick look at some data sheets didn't shed any light on this, but the wikipedia site is pretty good in general terms. I will open a few up in the lab at some stage soon and see if I can work out what is inside.

In any case, I wasn't implying that one should leave the gunk on the circuit board. As said, it is probably hygroscopic leading to all sorts of wonderful intermittent fault scenarios. It is also likely to be at least mildly corrosive - boric acid is not very corrosive to copper, but you can use it as flux, so best not to leave round your solder joints..