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Tantalum caps.

H

Henry Kolesnik

Jan 1, 1970
0
Over the last few years I've acquired quite a few consumer electronincs pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a
tantalum to repair some test equipment I was going to salvage a tantalum. I
couldn't find one anywhere, so I assume they're too expensive or too
unrelaible for high end consumer electronics. A couple of the boards were
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?
tnx
hank wd5jfr
 
J

John Popelish

Jan 1, 1970
0
Henry said:
Over the last few years I've acquired quite a few consumer electronincs pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a
tantalum to repair some test equipment I was going to salvage a tantalum. I
couldn't find one anywhere, so I assume they're too expensive or too
unrelaible for high end consumer electronics. A couple of the boards were
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?
tnx
hank wd5jfr

They can have very good characteristics (small size, low esr, high
parallel resistance and good capacitance stability) but have some
strange failure modes if they are misapplied. Digikey sells a great
variety of them. I can seldom justify their cost in production
designs, but use them quite often in one offs.
 
D

ddwyer

Jan 1, 1970
0
Henry Kolesnik said:
Over the last few years I've acquired quite a few consumer electronincs pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a
tantalum to repair some test equipment I was going to salvage a tantalum. I
couldn't find one anywhere, so I assume they're too expensive or too
unrelaible for high end consumer electronics. A couple of the boards were
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?
tnx
hank wd5jfr
twere always regarded as more reliable than aluminum; however there is
a failure mechanism associated with the source resistance and how close
the operating voltage is to the maximum specified.
Modern aluminum can have very low esr and an adequate alternative to
tantalum.
 
W

Watson A.Name \Watt Sun - the Dark Remover\

Jan 1, 1970
0
John said:
They can have very good characteristics (small size, low esr, high
parallel resistance and good capacitance stability) but have some
strange failure modes if they are misapplied. Digikey sells a great
variety of them. I can seldom justify their cost in production
designs, but use them quite often in one offs.

So in a production design, what would you use to get the equivalent
performance? An aluminum electrolytic in parallel with a ceramic?


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J

John Larkin

Jan 1, 1970
0
Over the last few years I've acquired quite a few consumer electronincs pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a
tantalum to repair some test equipment I was going to salvage a tantalum. I
couldn't find one anywhere, so I assume they're too expensive or too
unrelaible for high end consumer electronics. A couple of the boards were
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?
tnx
hank wd5jfr

We often use surface-mount tantalums on high-density, high-cost
boards. They are very reliable (don't dry out like aluminums) if used
carefully, but high peak currents can ignite them, so they are
generally a bad idea for bypassing power rails.

Polymer aluminums (don't dry out) or polymer tantalums (don't explode)
seem like a good idea, but I haven't tried them yet.

I think multilayer ceramics are pushing 100 uF these days.

John
 
J

John Popelish

Jan 1, 1970
0
Watson A.Name \"Watt Sun - the Dark Remover\" said:
John Popelish wrote: (snip)

So in a production design, what would you use to get the equivalent
performance? An aluminum electrolytic in parallel with a ceramic?

A production design usually pays for the engineering necessary to
reduce the need for premium quality components. Your solution is
often a cheaper alternative to a premium quality tantalum.
 
H

Henry Kolesnik

Jan 1, 1970
0
I have a Racal 9301A where a tantalum must have caught on fire because all
that was left was 2 leads, some crisp blackish ash and a little hardened
crust on the pcb where it burned. There's probaby 10 other tants on the
board and one or more are shorted but still intact and I'm trying to find
the bads one/ones with least effort without a schematic. The other unit is
a Wavetek 188-S1257 where a tantalum had a dead short but was intact. I
repalced it with an electrolytic. The cap is on a 15 volt rail where I
think it shorted and took out the regulator. Ireplace the regulator with
what I assumed was a good one out of a new box but it was bad and it put 23
volts on the rail that had a 20 volt rating but no more failed. Sometime I
have good luck.
73
hank wd5jfr
 
L

Lewin A.R.W. Edwards

Jan 1, 1970
0
Over the last few years I've acquired quite a few consumer electronincs pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a

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.

Computer equipment is a good source for tantalums - motherboards, hard
drive PCBAs, etc. Of course, it will be surface-mount :)
 
T

Tim Wescott

Jan 1, 1970
0
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.

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. Does anyone remember
the Great Tantalum Shortage of a couple of years ago? One of the big
tantalum supplying regions is central Africa, and a combination of wars
reducing supply and increased demand led to some supply problems for a
while -- I remember that at least one of the manufacturers even came out
with a Niobium cap as a substitute.
 
O

OK1SIP

Jan 1, 1970
0
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
 
J

Jeroen

Jan 1, 1970
0
John said:
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.
 
F

Fred

Jan 1, 1970
0
Jeroen said:
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!
 
B

Bill Turner

Jan 1, 1970
0
I have a Racal 9301A where a tantalum must have caught on fire because all
that was left was 2 leads, some crisp blackish ash and a little hardened
crust on the pcb where it burned. There's probaby 10 other tants on the
board and one or more are shorted but still intact and I'm trying to find
the bads one/ones with least effort without a schematic.

_________________________________________________________

One odd characteristic of tanalums is they will work with reversed
polarity for a while before failing. I have seen them inadvertently
installed backwards and get through test ok and out in the field before
failing.

Just something to be aware of. Aluminums normally fail immediately
under the same circumstances.
 
B

Bill Turner

Jan 1, 1970
0
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.
 
S

Spehro Pefhany

Jan 1, 1970
0
_________________________________________________________

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
 
J

John Larkin

Jan 1, 1970
0
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
 
J

John Larkin

Jan 1, 1970
0
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
 
D

Dr. Anton.T. Squeegee

Jan 1, 1970
0
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 where:

(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)
 
T

Tim Wescott

Jan 1, 1970
0
John Larkin said:
On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott"


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.
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.
 
K

Ken Finney

Jan 1, 1970
0
John Larkin said:
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.
 

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