Electrolytic Capacitor Voltage

C

Costas Vlachos

Guest
If a 100V aluminium electrolytic cap (say, 10uF @ 100V) is used on a 5V
circuit, will it be OK? I mean, will the capacitance drop or the performance
of the cap affected as a result of using it at a much lower voltage that its
rated voltage? Would it be better to use a 16V cap for instance? I'm asking
in terms of performance, not cost.

Many thanks.

Costas
 
"Costas Vlachos" <c-X-vlachos@hot-X-mail.com> wrote in message
news:bepia0$t6s$1@sparta.btinternet.com...
If a 100V aluminium electrolytic cap (say, 10uF @ 100V) is used on a 5V
circuit, will it be OK? I mean, will the capacitance drop or the
performance
of the cap affected as a result of using it at a much lower voltage that
its
rated voltage? Would it be better to use a 16V cap for instance? I'm
asking
in terms of performance, not cost.

Many thanks.

Costas


I would wonder if the cap will form properly over time
at such a large voltage difference.
I would expect, in terms of performance for it to work
in most circuits and to pass higher voltage varriations
than a 6-16V capacitor. (which might not be wanted)
Jeff
 
"Costas Vlachos" <c-X-vlachos@hot-X-mail.com> wrote in message
news:bepia0$t6s$1@sparta.btinternet.com...
If a 100V aluminium electrolytic cap (say, 10uF @ 100V) is used on a 5V
circuit, will it be OK? I mean, will the capacitance drop or the
performance
of the cap affected as a result of using it at a much lower voltage that
its
rated voltage? Would it be better to use a 16V cap for instance? I'm
asking
in terms of performance, not cost.

Many thanks.

Costas
If space constraints aren't an issue, it should work out fine.
If you need to save space (assuming it's going in a project box), then of
course the the 10v or 16v caps are generally smaller than the 100v.
Then again, if cost isn't an issue, you can get special miniature 100v
caps -- I don't recall offhand whether they're Sprague, Nichicon or Rubycon,
but I think Digi-Key has the small profile caps.
 
I'm no expert but here's 2c for you:
My understanding of how electrolytic caps work is that the electrolyte
inside of the cap forms into a polarized state when charged with an applied
voltage. I have read that if you don't charge an electrolytic cap with a
"nominal" voltage then it never forms properly and eventually fails to
function properly. The opinion on "nominal" voltage varies widely - I use a
1.5x applied dc voltage rule of thumb for first filter cap in power supply
filtering applications and perhaps 15% over actual applied voltage for local
bypass & etc applications.


"Costas Vlachos" <c-X-vlachos@hot-X-mail.com> wrote in message
news:bepia0$t6s$1@sparta.btinternet.com...
If a 100V aluminium electrolytic cap (say, 10uF @ 100V) is used on a 5V
circuit, will it be OK? I mean, will the capacitance drop or the
performance
of the cap affected as a result of using it at a much lower voltage that
its
rated voltage? Would it be better to use a 16V cap for instance? I'm
asking
in terms of performance, not cost.

Many thanks.

Costas
 
todd@nospamprepair.com wrote:
I'm no expert but here's 2c for you:
My understanding of how electrolytic caps work is that the electrolyte
inside of the cap forms into a polarized state when charged with an applied
voltage. I have read that if you don't charge an electrolytic cap with a
"nominal" voltage then it never forms properly and eventually fails to
function properly. The opinion on "nominal" voltage varies widely - I use a
1.5x applied dc voltage rule of thumb for first filter cap in power supply
filtering applications and perhaps 15% over actual applied voltage for local
bypass & etc applications.
The capacitor is formed at the factory. If you installed an un
formed capacitor in a piece of equipment, it wouldn't work. It is
formed by applying a small current at the rated voltage. Some older
capacitor testers like the Sprague TO series capacitor analyzers allowed
you to re-form old capacitors that had been in storage for a long time.

Here is an example of a Sprague TO-5
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2545213871&category=25408>
--


Michael A. Terrell
Central Florida
 
todd@nospamprepair.com wrote:
Thanks Michael - but do they not become un-formed or in some other way
useless when used in applications where the working voltage is way low in
relation to the caps rated voltage as the original poster was asking?

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:3F18F38E.54EAA80B@earthlink.net...
todd@nospamprepair.com wrote:

I'm no expert but here's 2c for you:
My understanding of how electrolytic caps work is that the electrolyte
inside of the cap forms into a polarized state when charged with an
applied
voltage. I have read that if you don't charge an electrolytic cap with a
"nominal" voltage then it never forms properly and eventually fails to
function properly. The opinion on "nominal" voltage varies widely - I
use a
1.5x applied dc voltage rule of thumb for first filter cap in power
supply
filtering applications and perhaps 15% over actual applied voltage for
local
bypass & etc applications.

The capacitor is formed at the factory. If you installed an un
formed capacitor in a piece of equipment, it wouldn't work. It is
formed by applying a small current at the rated voltage. Some older
capacitor testers like the Sprague TO series capacitor analyzers allowed
you to re-form old capacitors that had been in storage for a long time.

Here is an example of a Sprague TO-5

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2545213871&category=2540
8
--


Michael A. Terrell
Central Florida
Some types of electrolyte deteriorate with age, and need reformed to
specified voltage. Newer, high quality electrolytics have very little
problems with them un-forming, but the re-forming feature also tests
leakage current at your selected voltage. This is good to use to test a
sample of a new part at its full rated voltage to see how well they were
formed. Some brands or series are crap, while most brands or series
meet their specifications with no problems.
--


Michael A. Terrell
Central Florida
 
"Costas Vlachos" <c-X-vlachos@hot-X-mail.com> wrote in message
news:bepia0$t6s$1@sparta.btinternet.com...
If a 100V aluminium electrolytic cap (say, 10uF @ 100V) is used on a 5V
circuit, will it be OK? I mean, will the capacitance drop or the
performance
of the cap affected as a result of using it at a much lower voltage that
its
rated voltage? Would it be better to use a 16V cap for instance? I'm
asking
in terms of performance, not cost.

Many thanks.

Costas
ISTR that leakage current increases exponentially with increasing voltage,
and the oxygen in the electrolyte is consumed faster with higher leakage.

Oxygen consumed so leakage increases so more oxygen consumed so... !

I've seen one product with electrolytics running at full working voltage.
Didn't last very long before failing! Wonder if they do this in camcorders?
:)

Paul
 

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