Re: Caution - InterAv "Spike Guard" Capacitor

[Robert Bonomi]

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

[Model Flyer]

"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
>
>

[Jim Weir]

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

[Robert Bonomi]

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.

[Jim Weir]

Roughly...zero.

Jim


Ernest Christley >
shared these priceless pearls of wisdom:

->
->Don't know how much this applies, but I worked at a custom electronics
->manufacturer.


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

[MikeremlaP]

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.

[James M. Knox]

"Peter Gottlieb" > wrote in
t:

> Ooooh, that melted down big time. Looks like it arced in there.
> I think the one that looks like a pestle, that can still be unwrapped
> if you try.
> This unit may have consisted of three paralleled rolls, but, just
> guessing without closer examination.

Yeah, if you don't mind getting your hands dirty (again) try Peter's theory
to see if you can unroll some of the insides.

The capacity goes up linearly as a function of the surface area, but as the
square (if I recall) of the separation of the conductors. No way in heck
you are going to get 6000 uF out of one rod in the middle, with a big gap
to the outer can.

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

[Jim Weir]

In the FPS system,

C = 0.224 (KA/d)(n-1)

K= dielectric constant
A= area of one side of one plate in square inches
d= separation of plate surfaces in inches
n= number of plates

No square term, sorry.

Jim


"James M. Knox" >
shared these priceless pearls of wisdom:

->
->The capacity goes up linearly as a function of the surface area, but as the
->square (if I recall) of the separation of the conductors.
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Peter Gottlieb]

The 1/d term is what gets the high values for capacitance when you have a
small "d," as in microinches.


"Jim Weir" > wrote in message
...
> In the FPS system,
>
> C = 0.224 (KA/d)(n-1)
>
> K= dielectric constant
> A= area of one side of one plate in square inches
> d= separation of plate surfaces in inches
> n= number of plates
>
> No square term, sorry.
>
> Jim
>
>
> "James M. Knox" >
> shared these priceless pearls of wisdom:
>
> ->
> ->The capacity goes up linearly as a function of the surface area, but as
the
> ->square (if I recall) of the separation of the conductors.
> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
> http://www.rst-engr.com

[MikeremlaP]

Hi guys:

Probably getting off topic a bit, although my original concern was safety of
flight, and things shorting out. Are we agreed that this type of capacitor
construction is too prone to vibration for aircraft use and that it has a bad
failure mode?

I cut into the guts of the cap - I'm still clueless. Guess some reading is in
order on my part. If someone wants to educate me, either on or off line...

The 2nd cut photo is here:

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

Mike Palmer <><
Excellence in Ergonomics

[Peter Gottlieb]

Ok, here's what I see:

It was potted with some sort of goo to prevent the innards from vibrating.
It looks like it was a single jelly roll electrolytic. It must have shorted
and arced, and the arc melted the foil roll into a glob and the remaining
jelly roll with a globbed end. It did short, and could keep shorting
intermittently. The arcing could also have possibly breached the can,
although clearly not in this case. There may have been design features to
mitigate this possibility.

Peter


"MikeremlaP" > wrote in message
...
> Hi guys:
>
> Probably getting off topic a bit, although my original concern was safety
of
> flight, and things shorting out. Are we agreed that this type of
capacitor
> construction is too prone to vibration for aircraft use and that it has a
bad
> failure mode?
>
> I cut into the guts of the cap - I'm still clueless. Guess some reading
is in
> order on my part. If someone wants to educate me, either on or off
line...
>
> The 2nd cut photo is here:
>
> http://www.fotolog.net/palmer_mp/
>
> Mike Palmer <><
> Excellence in Ergonomics
>