Caution - InterAv "Spike Guard" Capacitor

In article ,
Jim Weir wrote:
Ah, no sir, sorry. You may want to google how an electrolytic capacitor works.

I got my initial commercial 1st class broadcast engineer license in 1970.
I've got a fair library on the bookshelves.

But thanks the advice.

From Meade, "Foundations of Electronics", from which I've been teaching freshman
engineering students for a few years now...

"The external aluminum can, or housing, is typically the negative plate (or
electrode). The positive electrode external contact is generally aluminum foil
immersed or in contact with an electrolyte of ammonium borate (or equivalent).

...

To create the dielectric, a dc current is passed through the capacitor. This
causes a very thin aluminum oxide film (about 10 microcm thick) to form on the
foil surface. THIS THIN OXIDE FILM IS THE DIELECTRIC."

Emphasis mine. Meade 1. Bonomi 0.


I fully understand the difference between electrolyte and dielectric.

I note that the dielectric was _not_ the subject under discussion.


Meade identifies two plates in the electrolytic capacitor -- the first
being (usually) the can; the second being the foil. I do maintain that the
electrolyte is 'between' those two plates.

Furthermore, I've used electrolytic capacitors that were constructed
with two foil plates, which did *not* use the 'can' as part of the circuit.
You get significantly higher capacitance values that way -- in the same
_physical_ space --by minimizing the 'distance' of the ion transference.

If one _was_ discussing the characteristics of the dielectric, it would be
appropriate to call it "dielectric materialism". groan Which I will
stay away from, other than to note that if the electrolyte is _not_ present
between the plates of the capacitor, then the dielectric does _not_ form
when current is supplied. And all you have is the equivalent of an 'air gap'
type with a surface area approximating that of the 'can', in the case where
the can is used as the negative plate. In the case of a 'dual foil' plate
design, the usual result of loss of electrolyte is an "arc-over", aka short,
between the plates. A "catastrophic" failure of a near-explosive proportions..


Jim


bonomi@c-ns. (Robert Bonomi)
shared these priceless pearls of wisdom:

-
-The electrolyte in a capacitor, just like in a battery, is what is _between_
-the plates.

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

"Robert Bonomi" bonomi@c-ns. wrote in message
...
In article ,
Jim Weir wrote:

the can is used as the negative plate. In the case of a 'dual
foil' plate
design, the usual result of loss of electrolyte is an "arc-over",
aka short,
between the plates. A "catastrophic" failure of a near-explosive
proportions..


Had a nice failure with a 150mf 400 volt eletrolitic, the top blew
out as if you fired a .22 bullet through it. This was caused by a
power surge caused by the supply company. Apart from the cap in the
monitors psu, it also blew, the psu of a printer, the computer psu,
the microwave, cooker and Hi-Fi system. A few other household
electrical items were damaged as well.:-)
--

..
--
Cheers,
Jonathan Lowe
modelflyer at antispam dot net

Antispam trap in place



Jim


bonomi@c-ns. (Robert Bonomi)
shared these priceless pearls of wisdom:

-
-The electrolyte in a capacitor, just like in a battery, is what
is _between_
-the plates.

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

bonomi@c-ns. (Robert Bonomi)
shared these priceless pearls of wisdom:


-
-I got my initial commercial 1st class broadcast engineer license in 1970.
-I've got a fair library on the bookshelves.


If you want to play old-fart one-upmanship, my 1st phone was in 1959 on my 16th
birthday. I believe that 16 was the limit back in 'dem golden oldie days. I
did third, second, and first all in one sitting. That, of course, was to
supplement my ham ticket which I had obtained in '57.

And I'm not about to play "mine is bigger than yours" only to state that I've
got a few books on my shelves, too. Two of which I haven't even colored yet
{;-)

Nor am I about to go on and on about a simple question since the resolution is
that even shorted, this device isn't going to fail catastrophically.

In practice, a shorted electrolytic (save physical "mash" damage) is about as
rare as a shorted resistor. RST's gone through, what, half a million of them in
30 years without a shorted one yet. A couple of dozen opens, but no shorts.
That seems to be the industry trend.

Jim



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

In article ,
Jim Weir wrote:
bonomi@c-ns. (Robert Bonomi)
shared these priceless pearls of wisdom:


-
-I got my initial commercial 1st class broadcast engineer license in 1970.
-I've got a fair library on the bookshelves.


If you want to play old-fart one-upmanship, my 1st phone was in 1959 on my 16th
birthday. I believe that 16 was the limit back in 'dem golden oldie days. I
did third, second, and first all in one sitting.

16 was still the minimum in '70. I was about 3 mo short of turning 17.
(They were administered locally only once every six months.) I took 'em all
in one sitting, too.

That, of course, was to
supplement my ham ticket which I had obtained in '57.

And I'm not about to play "mine is bigger than yours" only to state that I've
got a few books on my shelves, too. Two of which I haven't even colored yet
{;-)

I won't mention my complete collection of Dr. Seuss, either.

Nor am I about to go on and on about a simple question since the resolution is
that even shorted, this device isn't going to fail catastrophically.

Other people have direct experience to the contrary.


In practice, a shorted electrolytic (save physical "mash" damage) is about as
rare as a shorted resistor.

I'll agree with that -- while noting that wire-wound resistors _can_ short.

RST's gone through, what, half a million of them in
30 years without a shorted one yet.

I've got a far smaller 'sample population', probably only in the low-middle
4 figures. I've seen _one_ that was an 'open' -- factory defect; _no_ innards
whatsoever. I've also had *four* explode due to short. Admittedly, I don't
think they were _less_ than 30 years old.

A couple of dozen opens, but no shorts.
That seems to be the industry trend.

Okay guys, I cut the cap open.

See foto at

http://www.fotolog.net/palmer_mp/

No foil that I can see. In fact, I'm not sure how this thing works. I thought
the idea was to create maximum surface area.

I probably should have buzzed the negative terminal to the can to see if
connected. (Can do that tomorrow).

Black stuff has a strong order to it...

In any event, it seems that, with vertical mounting, lugs down, either
component could rattle its way to short the inputs. I'm surprised it didn't
happen.

Mike Palmer
Excellence in Ergonomics, but apparently obsolete in Electrical Engineering.