Hi all,
tantalum caps seem to be too expensive for consumer-grade equipment.
They contain pricey material - silver and, of course, tantalum, so
making them cheaper is impossible. AFAIK they are widely used in
military-grade equipment, where the price is not an issue. Their main
advantages are a longer life (they do not dry out nor leak) and a
bigger temperature range (frost resistance).
About using cheap parts in consumer electronics: At least 80 percent
of failures of certain types of TV sets were caused by dried-out
aluminum caps. The good practice when repairing these sets was: first
check all electrolyte caps by adding a good one in parralel. It was
successful very often.

BR from Ivan

John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.

"Jeroen" wrote in message
...
John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.


I didn't think it was quite as bad as that. Also very temperature
dependent. These type of ceramics are also pyroelectric as well as being
piezoelectric!

On Thu, 22 Jan 2004 05:05:22 -0800, the renowned Bill Turner
wrote:

On 21 Jan 2004 19:09:37 -0800, (Lewin A.R.W. Edwards)
wrote:

Consumer electronics are costed down to the lowest possible level. If
they can use something cheaper, they WILL use something cheaper. A TV
set or VCR has had people go over the design hundreds of times with
BOMs and catalogs, checking to see if they can shave a penny here or a
penny there.

_________________________________________________ ________

Well, maybe. Any manufacturer who has been nailed with thousands of
dollars in warranty costs caused by saving a penny might disagree with
your statement. I've seen it happen.

Caused by bad engineering (or purchasing), I would say.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Thu, 22 Jan 2004 08:54:58 +0100, Jeroen
wrote:

John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.


Which opens up the possibility of using them as parametric amplifiers
or modulators. I have a paper somewhere that uses the nonlinearity of
ceramic caps to make a nonlinear transmission line - a shock line -
that sharpens the rising edge speed of kilovolt pulses.

John

On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott"
wrote:

I wouldn't assume that just because your test equipment comes to you broken
is a result of tantalum caps -- perhaps your sample is skewed by buying at
hamfests instead of burgling active technology companies? Maybe if you only
acquired your home entertainment equipment from dumpsters you'd conclude
that aluminum electrolytics are bad?

I recently escaped from a company that does aero (but not space) systems.
They get mounted on aircraft and are expected to survive being shipped in an
unpressurized cargo hold at 50000 feet. At that altitude a wet aluminum
electrolytic will dry out, but a tantalum will be fine. There are even
wet-slug tantalums for high-altitude applications that will not dry out at
these altitudes.


Wet-slug tants are expensive (do they still have silver cases?) but
don't blow up like the dry ones. The dry slugs coat the sintered
tantalum (fuel) with MnO2 (oxidizer).


The problems with tantalum are their fragility (we've had exploding caps on
our boards, with one manufacturer's part being fine and another being
horrid), cost, and the relative scarcity of tantalum.

This is really erratic. One spool of tants will be bombs, another
can't be made to fail by deliberate abuse.

John

In article ,
says...

snippety

from my personal stuff purchased new. One example is a MGA Mitsubishi rear
projection TV that operated flawlessly for nearly 20 years of daily use.
Most of my test equipment comes from hamfests and is surplus after becoming
obsolete and non-operative in less than 20 years. That leads me to wonder
what the real story is behind tantalum capacitors. What do the experts have
to say?

The ONLY problems I've ever had with tantalums are whe

(1) The part was defective from the manufacturer.

(2) The voltage rating was consistently exceeded.

(3) The thing was installed backwards (reverse polarity).

I have no less than five Tektronix O-scopes here, all vintage
late-70's to mid-80's. This means not one of them is less than 20 years
old. They all use lots of tantalums, and they all work great, but then
again Tek was (in those days) proud of what they put out, and was most
definitely engineer-driven (which means at least a 20% 'fudge factor'
built into everything they made).

Tantalum caps are very stable and durable, but they are much more
costly than aluminum types. In consumer electronics, the manufacturers
will try to shave every penny they can off the cost of the design, often
contrary to good common (engineering) sense.

Such considerations are (usually) not so critical when it comes to
non-consumer stuff.

Keep the peace(es).

--
Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
kyrrin a/t bluefeathertech d-o=t c&o&m
Motorola Radio Programming & Service Available -
http://www.bluefeathertech.com/rf.html
"Quando Omni Flunkus Moritati" (Red Green)

"John Larkin" wrote in
message ...
On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott"
wrote:


snip

Wet-slug tants are expensive (do they still have silver cases?) but
don't blow up like the dry ones. The dry slugs coat the sintered
tantalum (fuel) with MnO2 (oxidizer).

Boy are they ever. I have some surplus ones, but they have cases that are
more of a silver-gray than that nice yellowish-white look you get from
silver-plated connectors. These are special parts, but if you want a
generally high-performance cap in a (relatively) small package they're hard
to beat.

I worked for a while on a project to make a power-wire networking device.
During testing I accidentally dragged a scope ground across a circuit that
was referenced to the 115V power line, thereby exceeding the tantalum cap's
voltage rating -- er -- "slightly". Little pieces of flaming capacitors
bounced around the lab. After that all of my digital logic (3.3V and lower)
coworkers _never_ messed with my bench.

The problems with tantalum are their fragility (we've had exploding caps
on
our boards, with one manufacturer's part being fine and another being
horrid), cost, and the relative scarcity of tantalum.

This is really erratic. One spool of tants will be bombs, another
can't be made to fail by deliberate abuse.

Interesting. I'll have to remember that. Thanks. In any case when
designing with _any_ electrolytic capacitor it's best to use specify a cap
for 20-50% higher voltage than what you think it's ever going to see,
particularly because many voltage regulators overshoot on power up and the
output cap sees more voltage than you think.

John

"John Larkin" wrote in
message ...
On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott"
wrote:

I wouldn't assume that just because your test equipment comes to you
broken
is a result of tantalum caps -- perhaps your sample is skewed by buying
at
hamfests instead of burgling active technology companies? Maybe if you
only
acquired your home entertainment equipment from dumpsters you'd conclude
that aluminum electrolytics are bad?

I recently escaped from a company that does aero (but not space) systems.
They get mounted on aircraft and are expected to survive being shipped in
an
unpressurized cargo hold at 50000 feet. At that altitude a wet aluminum
electrolytic will dry out, but a tantalum will be fine. There are even
wet-slug tantalums for high-altitude applications that will not dry out
at
these altitudes.


Wet-slug tants are expensive (do they still have silver cases?) but
don't blow up like the dry ones. The dry slugs coat the sintered
tantalum (fuel) with MnO2 (oxidizer).


snip

Silver cased wet slug tantalums DO explode, most contracts that
allow the use of wet slugs require the use of tantalum cased parts.

In article ,
Dr. Anton.T. Squeegee wrote:
In article ,
says...

snippety

from my personal stuff purchased new. One example is a MGA Mitsubishi rear
projection TV that operated flawlessly for nearly 20 years of daily use.
Most of my test equipment comes from hamfests and is surplus after becoming
obsolete and non-operative in less than 20 years. That leads me to wonder
what the real story is behind tantalum capacitors. What do the experts have
to say?

The ONLY problems I've ever had with tantalums are whe

(1) The part was defective from the manufacturer.

(2) The voltage rating was consistently exceeded.

(3) The thing was installed backwards (reverse polarity).

I have no less than five Tektronix O-scopes here, all vintage
late-70's to mid-80's. This means not one of them is less than 20 years
old. They all use lots of tantalums, and they all work great, but then
again Tek was (in those days) proud of what they put out, and was most
definitely engineer-driven (which means at least a 20% 'fudge factor'
built into everything they made).

Tantalum caps are very stable and durable, but they are much more
costly than aluminum types. In consumer electronics, the manufacturers
will try to shave every penny they can off the cost of the design, often
contrary to good common (engineering) sense.

Such considerations are (usually) not so critical when it comes to
non-consumer stuff.

Tektronix was, during that time, strongly discouraging all new designs from
using tantalums. IIRC they had been taken to court over a case in which
a 465 'scope (the original, not the plastic follow-ons) had spontaneously
ignited and had resulted in an expensive fire. Forensics revealed that
a tantalum power-supply bypass cap had started the conflagration. The
drive to reduce tantalum usage was driven primarily by this liability issue,
more than component cost. If you wanted to use a tantalum, you had to
justify its usage to the component/design review committees -- which wasn't
difficult if you had good reasons and your design was solid.

-frank
(ex-Tekie)
--