General Questions about Tantalum and Electrolytic Capacitors

[Bernhard Krämer]

Hello,

While working on my circuit, I found that I have some basic questions about
simple capacitors:

1)
Is there any minimum operating voltage for Tantalum and Electrolytic
capacitors?
I think that the formation of an electrolytic layer in such a capacitor
could perhaps require some minimum operating voltage.

2)
Until which frequencies does an electrolytic capacitor work well? When
should I consider tantalum capacitors?

 

[Mark]

1 generally no

2 the main diff between al and tan is the ESR especially at low
temperatures. ESR = Effective series resistance

A second diff is leakage (shunt resistance) , tant are lower leakage
(higher shunt resistance) generally.

Mark

 

[John Larkin]

1 generally no

2 the main diff between al and tan is the ESR especially at low
temperatures. ESR = Effective series resistance

A second diff is leakage (shunt resistance) , tant are lower leakage
(higher shunt resistance) generally.

Third diff is that al elecs gradually lose capacitance (over years or
decades) whereas tants like to explode violently if enough current is
available.

John

 

[Joerg]

Hello John,

Third diff is that al elecs gradually lose capacitance (over years or
decades) whereas tants like to explode violently if enough current is
available.

Depends on who makes them. I have elecs in old radios that are around 50
years old and when last measured still had their 10uF or whatever and
little leakage. Some are from companies that stopped making caps when I
was in diapers. I usually check these electrolytics when I repair or
restore a vintage radio.

But then again there were certain PC motherboard caps that had a life
span of a few weeks, I heard.

Tant explosions: I remember when they stuffed a proto board wrong, all
the tants reversed. Then it was connected to a 5V/100A supply. Some said
it was like popcorn, others likened it to a machine gun. We had to
replace some acoustic ceiling tiles later.

Regards, Joerg

 

[[email protected]]

Hello,

While working on my circuit, I found that I have some basic questions about
simple capacitors:

1)
Is there any minimum operating voltage for Tantalum and Electrolytic
capacitors?
I think that the formation of an electrolytic layer in such a capacitor
could perhaps require some minimum operating voltage.

2)
Until which frequencies does an electrolytic capacitor work well? When
should I consider tantalum capacitors?

Over long periods the working voltage of trolytics drops if that
working voltage isnt applied. Unlikely to get you into trouble, but can
if the thing is stored 20 years unused then needed.

The good side is they they will reform, but whether theyll reform in
use depends onteh circuit, and whether the circuit will function
meantime is another question.

But by far the most important difference is that tants are prettier.


NT

 

[Ross Herbert]

Hello John,


Depends on who makes them. I have elecs in old radios that are around 50
years old and when last measured still had their 10uF or whatever and
little leakage. Some are from companies that stopped making caps when I
was in diapers. I usually check these electrolytics when I repair or
restore a vintage radio.

But then again there were certain PC motherboard caps that had a life
span of a few weeks, I heard.

Tant explosions: I remember when they stuffed a proto board wrong, all
the tants reversed. Then it was connected to a 5V/100A supply. Some said
it was like popcorn, others likened it to a machine gun. We had to
replace some acoustic ceiling tiles later.

Hemetically sealed (wet) tantalum's make a bigger bang than solid
tantalum's.

 

[Robert Baer]

Third diff is that al elecs gradually lose capacitance (over years or
decades) whereas tants like to explode violently if enough current is
available.

John

However, one can make an aluminum electrolytic explode like a
firecracker (lots of paper seen afterwards) if excessive voltage is applied.

 

[Robert Baer]

Over long periods the working voltage of trolytics drops if that
working voltage isnt applied. Unlikely to get you into trouble, but can
if the thing is stored 20 years unused then needed.

The good side is they they will reform, but whether theyll reform in
use depends onteh circuit, and whether the circuit will function
meantime is another question.

But by far the most important difference is that tants are prettier.


NT

A trick used to reform the aluminum capacitors on Tektronix tube
scopes was to slowly raise the input line voltage with a variac.
The idea is to have a capacitor voltage increased slowly, to minimize
internal leakage currents and possible damage.

 

[[email protected]]

[email protected] wrote: prettier.


A trick used to reform the aluminum capacitors on Tektronix tube
scopes was to slowly raise the input line voltage with a variac.
The idea is to have a capacitor voltage increased slowly, to minimize
internal leakage currents and possible damage.

That works nicely with transistorised kit.

With the old valve stuff that needs reforming, the rectifier valve
starts to conduct over a very small v range, so you have to wind the
variac up very slowly indeed around that area to get that method to
work.

I've reformed 1930s 'lytic caps that way, though not with 100% success,
but earlier kit tends to use paper caps housed in wax, and I've not
found any way to deal with those. Can they be oven cooked at just above
100C safely? If so it might be poss to dry them out that way.


NT

 

[John Larkin]

However, one can make an aluminum electrolytic explode like a
firecracker (lots of paper seen afterwards) if excessive voltage is applied.

Sure, but you have to furnish enough energy to make the bang, and you
generally have to exceed the cap's specs. An MnO2 tantalum provides
its own explosive chemical energy, and they detonate when operated
well within their ratings. The new polymer tants are better.

John

 

[Joerg]

Hello John,

Sure, but you have to furnish enough energy to make the bang, and you
generally have to exceed the cap's specs. An MnO2 tantalum provides
its own explosive chemical energy, and they detonate when operated
well within their ratings. The new polymer tants are better.

But electrolytics can explode "nicer". Not by excess voltage but when I
exceeded the current rating for too long one of them (a really big one)
sent its aluminum can skywards. Straight up like a Saturn V except that
the ceiling was in the way. It also made a nice roaring sound. The paper
then flocked down like snow in a fairy tale.

That day I learned that there is indeed such a thing as a maximum
current rating for caps.

Regards, Joerg

 

[Joerg]

Hello Bigcat,

Over long periods the working voltage of trolytics drops if that
working voltage isnt applied. Unlikely to get you into trouble, but can
if the thing is stored 20 years unused then needed.

Depends on who made the cap. I have some that are fine after 40-50 years
on the shelf. True new-old-stock.

The death sentence for an old cap in, say, a radio or a TV is when
replacing an old selenium rectifier with silicon diodes. Unless there is
a power resistor in series it can blow the cap right out of its moorings.

Sometimes, to preserve the antique look, I have scraped out a cap and
mounted a modern electrlytic in the can. That way it still looks like
the old can. The most pretty can was a Ducati cap. I guess that this
motorcycle company must have made caps for a while after WW2 until the
cycle biz picked up again. Maybe to tide them over the economic slump.

Regards, Joerg

 

[Ben Bradley]

Hello,

While working on my circuit, I found that I have some basic questions about
simple capacitors:

1)
Is there any minimum operating voltage for Tantalum and Electrolytic
capacitors?

Firstly, a little terminology: Tantalums are electrolytics too,
just made with something more expensive (or it's a more expensive
process), what are commonly called electrolytics are technically
"aluminum electronlyics."
So tantalum is short for tantalum electrolytic, and electrolytic is
short for aluminum electronlytic. This shorthand also gets by having
to used the alternative international spelling/pronunciation of
aluminum/aluminium.

I'm don't know about tantalums, but I've heard suggestions that
electrolytics be operated at at least half their max rated operating
voltage, else they're more likely to lose capacitance over the long
term (several years). It's also suggested that anything that has
electrolytics in it be powered up for at least a few minutes about
every six months or so, so the electolytics get voltage and don't
deform.
Have you looked at capacitor manufacturers' websites? Surely they
would have something on this.

I think that the formation of an electrolytic layer in such a capacitor
could perhaps require some minimum operating voltage.

I'm sure it's related - the initial forming of the layer in
manufacturing is done by applying a voltage.

2)
Until which frequencies does an electrolytic capacitor work well? When
should I consider tantalum capacitors?

You have to get info on the ESR and inductance of whatever
particular value of capacitor (and for the manufacturer and type) you
use, to decide if it's acceptable at the frequency you use. Many of
the better "suitable for switching power supply use" electrolytics
work fine into the hundreds of kHz. The Digikey catalog has some short
blurbs about each type of capacitor and what applications it might be
best for, but again, the maker's websites ought to have the best info.

 

[John - KD5YI]

Hello,

While working on my circuit, I found that I have some basic questions about
simple capacitors:

1)
Is there any minimum operating voltage for Tantalum and Electrolytic
capacitors?
I think that the formation of an electrolytic layer in such a capacitor
could perhaps require some minimum operating voltage.

2)
Until which frequencies does an electrolytic capacitor work well? When
should I consider tantalum capacitors?

Lots of really great information...

http://www.cornell-dubilier.com/framepdf.htm

Enjoy.

John

 

[Matt Flyer]

Hello,

While working on my circuit, I found that I have some basic questions about
simple capacitors:

1)
Is there any minimum operating voltage for Tantalum and Electrolytic
capacitors?
I think that the formation of an electrolytic layer in such a capacitor
could perhaps require some minimum operating voltage.

2)
Until which frequencies does an electrolytic capacitor work well? When
should I consider tantalum capacitors?

A couple of differences that I am aware of:
1 - Tantalums tend to have a higher capacitance for their size.
2 - Aluminum Electrolytics performance tends to degrade as they age.
This may be an issue if you are using them for de-coupling.
3 - Tantalum supposedly works better at high frequencies (you will need
to compare datasheets and look the ESR and ESL)

 

[John Larkin]

A couple of differences that I am aware of:
1 - Tantalums tend to have a higher capacitance for their size.
2 - Aluminum Electrolytics performance tends to degrade as they age.
This may be an issue if you are using them for de-coupling.
3 - Tantalum supposedly works better at high frequencies (you will need
to compare datasheets and look the ESR and ESL)

4. Tantalums are more expensive.

5. Tantalums explode.

John