Maker Pro
Maker Pro

Noise in electrolytic capacitors

N

Nemo

Jan 1, 1970
0
I am trying to evaluate whether to use tantalum versus OS-CON aluminium
electrolytics as the output decouplers for some linear postregulators
after a (relatively low noise) switcher. This is for a high gain
amplifier that will be operating down to audio frequencies. I've come
across references to aluminium electrolytics being noisy, but no firm
details (kind of odd as there are lots of details about ceramics'
problems under bias, wet vs dry tantalums etc). There's also some
references to "low noise" aluminium electrolytics for audio work, but I
don't know whether to take them seriously as audiophools believe all
kinds of weird stuff. So, can anyone advise if aluminium electrolytics -
specifically low ESR solid electrolyte types - have some kind of noise
problem? I know tants are NOT microphonic but I've not come across any
info about electrolytics and microphony one way or another.

Assuming they do not, I favour them over tants because their ESR is
lower, I get the impression that tants' ESR is poorer at low
frequencies, and I can get electrolytics at higher voltages (I like to
run caps at about double their rated voltage under the impression this
improves their reliability). The load on these linear regs will be
fairly constant, so ripple current will be low.

Thank you,
 
A

Andrew Holme

Jan 1, 1970
0
Nemo said:
I am trying to evaluate whether to use tantalum versus OS-CON aluminium
electrolytics as the output decouplers for some linear postregulators after
a (relatively low noise) switcher. This is for a high gain amplifier that
will be operating down to audio frequencies. I've come across references to
aluminium electrolytics being noisy, but no firm details (kind of odd as
there are lots of details about ceramics' problems under bias, wet vs dry
tantalums etc). There's also some references to "low noise" aluminium
electrolytics for audio work, but I don't know whether to take them
seriously as audiophools believe all kinds of weird stuff. So, can anyone
advise if aluminium electrolytics - specifically low ESR solid electrolyte
types - have some kind of noise problem? I know tants are NOT microphonic
but I've not come across any info about electrolytics and microphony one
way or another.

Assuming they do not, I favour them over tants because their ESR is lower,
I get the impression that tants' ESR is poorer at low frequencies, and I
can get electrolytics at higher voltages (I like to run caps at about
double their rated voltage under the impression this improves their
reliability). The load on these linear regs will be fairly constant, so
ripple current will be low.

Thank you,

I tested ceramic, poly layer, tant and electrolytic as integrator capacitors
in a PLL loop filter and I observed microphonics from all except the
electrolytic.
 
G

Gerhard Hoffmann

Jan 1, 1970
0
Nemo said:
frequencies, and I can get electrolytics at higher voltages (I like to
run caps at about double their rated voltage under the impression this
improves their reliability).

at half their rated voltage?

regards, Gerhard
 
N

Nemo

Jan 1, 1970
0
I said...
(I like to run caps at about double their rated voltage under the
impression this improves their reliability).

Ahh... meant I to write half their rated voltage. Well, it shows you
were paying attention! 8)

Thank you for the advice. OS-CONs it is!
 
F

Fred Bartoli

Jan 1, 1970
0
John Larkin a écrit :
I've never encountered noise from electrolytics. Considering that
self-discharge time constants are typically days or weeks, I can't
imagine a serious noise mechanism. Charge one up and see if it makes
noise.

Oh, sure there is: that's leakage current instabilities.
But I've found it significant only once, when doing my 200pV/rtHz
preamplifier where it had to go down to 0.1Hz
I had to resort to a bunch of bulky 2.2uF/250V polypro film caps.

BTW, caps microphony is only significant in "high impedance" circuits.
More precisely, the cut off frequency is given by the circuit loading
resistance x cap value.
 
B

Baron

Jan 1, 1970
0
Nemo Inscribed thus:
I can get electrolytics at higher voltages (I like to
run caps at about double their rated voltage under the impression this ^^^^^^
improves their reliability).

Thank you,

I'm glad I'm not in your lab. :)
 
F

Fred Abse

Jan 1, 1970
0
Oh, I sure did: pheeeooou ... *BOOM*

I once got the can off one in the crotch, from across the lab. Makes yer
eyes water ;-)
 
J

Joerg

Jan 1, 1970
0
Fred said:
I once got the can off one in the crotch, from across the lab. Makes yer
eyes water ;-)

Ouch, ouch ...

As a kid I was blissfully unaware of ESR and all those secondary
"non-essentials". Fluorescents dimmed ... wait, there's no dimmer on
that circuit ... *KABLOUIE* ... phsssooosh ... *POCK* ... phssss

Followed by some plaster raining down on me and a hissing and smoldering
can on the carpet. It had sailed mere inches past my right eye and I sat
there all shaking.

Had to spackle the crater in the ceiling, easy. Also had to get new
carpet, from a discount store five miles away, using my bicycle to
transport the large and heavy roll. Not so easy.

This was a serious capacitor, several hundred uF and a few hundred
volts, directly fed by a 230V/16A mains line. In a Cockcroft-Walton
tripler with numerous other caps feeding a kilowatt-size amplifier. In
hindsight it's all pretty amazing that I survived my childhood.
 
B

Ban

Jan 1, 1970
0
Joerg said:
Ouch, ouch ...

As a kid I was blissfully unaware of ESR and all those secondary
"non-essentials". Fluorescents dimmed ... wait, there's no dimmer on
that circuit ... *KABLOUIE* ... phsssooosh ... *POCK* ... phssss

Followed by some plaster raining down on me and a hissing and
smoldering can on the carpet. It had sailed mere inches past my right
eye and I sat there all shaking.

Had to spackle the crater in the ceiling, easy. Also had to get new
carpet, from a discount store five miles away, using my bicycle to
transport the large and heavy roll. Not so easy.

This was a serious capacitor, several hundred uF and a few hundred
volts, directly fed by a 230V/16A mains line. In a Cockcroft-Walton
tripler with numerous other caps feeding a kilowatt-size amplifier. In
hindsight it's all pretty amazing that I survived my childhood.

What a vivid imagination!

Ban
 
B

Ban

Jan 1, 1970
0
I meant the vivid desciption of your exploding components, you really can
differ between a failing MOSFET and passive parts, but nothing seems to beat
a tantal.
and by imagination was meant to be a special creative talent, unfortunately
I worded it ambivalent. ;)
Sorry but your telepathic crystal ball let you down, like before.

It happened with a Siemens electrolytic no less. Amplifier with PL509
tubes, tripler from 230VAC to about 900VDC. To be exact, this one,
made by yours truly:

http://www.analogconsultants.com/ng/images/PL509amp2.jpg

I was waiting for the crater in the ceiling tho.
ciao Ban
 
J

Joerg

Jan 1, 1970
0
Ban said:
I meant the vivid desciption of your exploding components, you really can
differ between a failing MOSFET and passive parts, but nothing seems to beat
a tantal.


The biggest tantalums I have ever encountered were the size of a
thimble. Their (frequent) explosions set off some nice and dazzling
greenish-orange clouds but the bang was quite modest. This one was a
serious beker type electrolytic cap, about 8cm long and maybe 4cm
diameter. Its aluminum tube including innards decided to become a
spacecraft. Went off like a champagne cork. I could have lost an eye in
that incident, scary.

and by imagination was meant to be a special creative talent, unfortunately
I worded it ambivalent. ;)

:)


I was waiting for the crater in the ceiling tho.


I was too shaken to take a photo back then. Plus after the loud bang my
dad came running down the stairs, expressed some rather immediate
ractions of disgust and that it should be fixed, and pronto. Then, he
saw the smoldering hole in the carpet ...

The only camera I had was a 6cm*6cm children's camera but even B&W film
was very expensive and I spent all my money on electronics. I wouldn't
have dared to ask dad for his Agfa 35mm camera at that moment. In
hindsight I understand his reaction. Back in the 60's it was financially
hard to build a house when your family had lots of kids and he didn't
want to see his dream burn down just because I had to have the biggest
honking amplifier in town.

For US readers: Homes in Germany have concrete ceilings (I wish they
also did here). There is a roughly 1/2" thick layer of gypsum-based
plaster applied to that ceiling which is either used as the base to
apply wallpaper or like in our case it was painted.
 
E

ehsjr

Jan 1, 1970
0
Tantalum meltdowns are about the nastiest electronics failure, 2nd
only to lithium ion battery explosions. The deal with tantalum is it
shoots out and then sticks like napalm. If it just went poof and
vaporized, that might be acceptable, but the flying material is
another story.

And the stinkiest is a selenium rectifier.

Ed
 
N

Nemo

Jan 1, 1970
0
Cool - this thread is turning into a guide to identifying components
from how they explode. This could be a valuable chapter in any
electronics textbook. To summarise so far:
And the stinkiest is a selenium rectifier.

Following the teasing I got about running electrolytics at 2 times their
rated voltage, when I meant to write half voltage, I then used a
transformer with the wrong turns ratio and put a 2.5 times overvoltage
on a couple of small OS-CONs. I can report they failed disappointingly
quietly, and apparently short-circuit: I only knew there was a problem
because the output collapsed to 2V. I can't help feeling that modern
components lack some of the 'character' of old fashioned electronics.
 
J

Joerg

Jan 1, 1970
0
Nemo said:
Cool - this thread is turning into a guide to identifying components
from how they explode. This could be a valuable chapter in any
electronics textbook. To summarise so far:


Following the teasing I got about running electrolytics at 2 times their
rated voltage, when I meant to write half voltage, I then used a
transformer with the wrong turns ratio and put a 2.5 times overvoltage
on a couple of small OS-CONs. I can report they failed disappointingly
quietly, and apparently short-circuit: I only knew there was a problem
because the output collapsed to 2V. I can't help feeling that modern
components lack some of the 'character' of old fashioned electronics.


If you want more sparkle try "modern" LDO regulators. For no apparent
reason they can go into up-chuck mode, become hot ... *POOF* ... nice
little crater.
 
B

Boris Mohar

Jan 1, 1970
0
I once got the can off one in the crotch, from across the lab. Makes yer
eyes water ;-)

Many moons ago I was staring at the top of this electrolytic cap that had a
solder safety vent on top. It was bulging and running hot. Suddenly the
vent blew and a volcano of hot electrolyte sprayed directly in my face.
Luckily I was wearing glasses so I escaped wit minor burns but got to keep my
eyesight.
 
Top