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Seeking low chemical reaction caps

P

Paul

Jan 1, 1970
0
Hi,

As you may know, Electrolytic caps can generate a few hundred
microvolts DC. I read that this voltage is due to slow chemical
reactions. What capacitors (over 4uF) generate the least DC voltage?

I appreciate it,
Paul L.
 
D

D from BC

Jan 1, 1970
0
Hi,

As you may know, Electrolytic caps can generate a few hundred
microvolts DC. I read that this voltage is due to slow chemical
reactions. What capacitors (over 4uF) generate the least DC voltage?

I appreciate it,
Paul L.

What's the app. ?


D from BC
 
H

Henry Kiefer

Jan 1, 1970
0
D said:
What's the app. ?

Try polymer caps, like OS-CON. I never measured it, but their electrolyt
is solid!

- Henry
 
P

Paul

Jan 1, 1970
0
What's the app. ?

D from BC



It's for a circuit that measures DC microvolts. Ceramics are better
than electrolytics, but in terms of microvolt levels they react to the
slightest vibration or an appreciable temperature change. What about
Poly films? They have self healing properties, so are there chemical
reactions occurring in Polys that may generate microvolts? As already
stated, electrolytics are out of the question.

Does anyone have any capacitor recommendations?
 
P

Paul

Jan 1, 1970
0
Try polymer caps, like OS-CON. I never measured it, but their electrolyt
is solid!

- Henry

--www.ehydra.dyndns.info



Thanks. The local store has some 4.7uF Mylars. I'd like to order some
from digikey, but there are so many types of polys and the datasheets
provide no hint of the caps chemical reaction factor -->

---
B
B32022
B32023
B32024
B32026
B32231
B32232
B32559
B32613
B32671
B32672
B32911
B32912
B32913
B32914
BF
BQ
CB
CombiSuppressor
E
ECH-U(B)
ECH-U(X)
ECHAX
ECHS
ECP-U(A)
ECQ-E(B)
ECQ-E(C)
ECQ-E(F)
ECQ-E(H)
ECQ-P(U)
ECQ-P(Z)
ECW-F(B)
ECW-F(L)
ECW-H(L)
ECW-H(V)
ECW-U(B)
ECW-U(C)
ECW-U(V16)
ECW-U(X)
ECW-UC(V17)
FB
FFV
M
MKP
MKP 416-420
MKP X1
MKP X2
MKT
MMKP 383
P
PETP
PPS
UNL
V
X-Y
366
460
462
464
940C
---
 
E

Eeyore

Jan 1, 1970
0
Paul said:
Hi,

As you may know, Electrolytic caps can generate a few hundred
microvolts DC.

Can they ? Into what load resistance ? Where did you hear this ?

Graham
 
E

Eeyore

Jan 1, 1970
0
Paul said:
Thanks. The local store has some 4.7uF Mylars. I'd like to order some
from digikey, but there are so many types of polys and the datasheets
provide no hint of the caps chemical reaction factor -->

There are no 'chemicals' to react in a plastic film cap.

Graham
 
H

Henry Kiefer

Jan 1, 1970
0
Eeyore said:
There are no 'chemicals' to react in a plastic film cap.

Every mylar should work.

Don't mix the technology names of polymer electrolytic caps with plastic
film caps! Even if some plastic films may be constructed out of chemical
polymers.

If you like a I can measure a OS-CON. But it will need a little time to
fully discharge it.

Tantals are also solid. Give them a try.


- Henry
 
D

D from BC

Jan 1, 1970
0
It's for a circuit that measures DC microvolts. Ceramics are better
than electrolytics, but in terms of microvolt levels they react to the
slightest vibration or an appreciable temperature change. What about
Poly films? They have self healing properties, so are there chemical
reactions occurring in Polys that may generate microvolts? As already
stated, electrolytics are out of the question.

Does anyone have any capacitor recommendations?

It's news to me about free electrolytics having a battery
characteristic.

Perhaps focus on the nature of the dielectrics.
You can start with vacuum sealed capacitors and then work your way up
in size until the capacitor is as big as the rest of the components.

A vacuum is an inert dielectric but not the best permittivity
especially compared to tantulum.

How is the capacitor being used?
As a filter?

Read up on:
http://en.wikipedia.org/wiki/Capacitor
D from BC
 
D

D from BC

Jan 1, 1970
0
Can they ? Into what load resistance ? Where did you hear this ?

Graham

Yeah.. This is new to me.. Electrolytics acting like an
electrochemical cell ???
I also suspect somebody is getting fooled by the bias current from
some voltage test equipment.

Foil impurities??
D from BC
 
D

D from BC

Jan 1, 1970
0
It's news to me about free electrolytics having a battery
characteristic.

Perhaps focus on the nature of the dielectrics.
You can start with vacuum sealed capacitors and then work your way up
in size until the capacitor is as big as the rest of the components.

A vacuum is an inert dielectric but not the best permittivity
especially compared to tantulum.

How is the capacitor being used?
As a filter?

Read up on:
http://en.wikipedia.org/wiki/Capacitor
D from BC

oopps... correction: 'work your way down in size'


D from BC
 
J

John Larkin

Jan 1, 1970
0
Yeah.. This is new to me.. Electrolytics acting like an
electrochemical cell ???
I also suspect somebody is getting fooled by the bias current from
some voltage test equipment.

Foil impurities??
D from BC


Good grief, he's right. I have a dusty bin of assorted lytics,
guaranteed not used for years, some not for decades. Six various caps
measure, in millivolts,

14
180
135
11
22
350

all in the "plus" direction.

I shorted that last one, the 350 mV guy, for 5 seconds. It dropped to
2 mV but is steadily charging itself back up, 10 mV now after a couple
of minutes.

That makes sense: aluminum plates of various purity and oxidation
level, some sorts of leadwires, all glopped with sulfuric acid and
additives.

Cool.

John
 
D

D from BC

Jan 1, 1970
0
Good grief, he's right. I have a dusty bin of assorted lytics,
guaranteed not used for years, some not for decades. Six various caps
measure, in millivolts,

14
180
135
11
22
350

all in the "plus" direction.

I shorted that last one, the 350 mV guy, for 5 seconds. It dropped to
2 mV but is steadily charging itself back up, 10 mV now after a couple
of minutes.

That makes sense: aluminum plates of various purity and oxidation
level, some sorts of leadwires, all glopped with sulfuric acid and
additives.

Cool.

John

For fun, maybe put a bunch of electrolytics in series and power up a
LCD watch. :)


D from BC
 
J

John Larkin

Jan 1, 1970
0
Good grief, he's right. I have a dusty bin of assorted lytics,
guaranteed not used for years, some not for decades. Six various caps
measure, in millivolts,

14
180
135
11
22
350

all in the "plus" direction.

I shorted that last one, the 350 mV guy, for 5 seconds. It dropped to
2 mV but is steadily charging itself back up, 10 mV now after a couple
of minutes.

That makes sense: aluminum plates of various purity and oxidation
level, some sorts of leadwires, all glopped with sulfuric acid and
additives.

Cool.

John

More:

Surface-mount MnO2 tantalums, right off the reel, initial charge in
mV:

300 33 uF 25v
730
820
1.2

150 47 uF 25v
70
4

I shorted the 820 mv guy for about 10 seconds and it went to 2 mv but
started recharging, to about 35 mv so far. Unloaded, it charges, but a
10M load pulls it back down.

A bunch of never-used polymer aluminum caps, United Chem-Com 100u/16v,
had initial voltages from 200 to 500 uv. I shorted one, and it went to
a few microvolts but is charging back up.

I suppose I could measure the short-circuit currents too.


So, avoid lytics in dc-sensitive circuits!

John
 
J

Jim Thompson

Jan 1, 1970
0
More:

Surface-mount MnO2 tantalums, right off the reel, initial charge in
mV:

300 33 uF 25v
730
820
1.2

150 47 uF 25v
70
4

I shorted the 820 mv guy for about 10 seconds and it went to 2 mv but
started recharging, to about 35 mv so far. Unloaded, it charges, but a
10M load pulls it back down.

A bunch of never-used polymer aluminum caps, United Chem-Com 100u/16v,
had initial voltages from 200 to 500 uv. I shorted one, and it went to
a few microvolts but is charging back up.

I suppose I could measure the short-circuit currents too.


So, avoid lytics in dc-sensitive circuits!

John

Lecher! STOP squeezing them ;-)

...Jim Thompson
 
More:

Surface-mount MnO2 tantalums, right off the reel, initial charge in
mV:

300 33 uF 25v
730
820
1.2

150 47 uF 25v
70
4

I shorted the 820 mv guy for about 10 seconds and it went to 2 mv but
started recharging, to about 35 mv so far. Unloaded, it charges, but a
10M load pulls it back down.

A bunch of never-used polymer aluminum caps, United Chem-Com 100u/16v,
had initial voltages from 200 to 500 uv. I shorted one, and it went to
a few microvolts but is charging back up.

I suppose I could measure the short-circuit currents too.

So, avoid lytics in dc-sensitive circuits!

John


You sure your DMM isn't charging the caps while you're measuring them?

M
 
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