| Author |
Message |
gmv
Guest
|
 Posted:
Fri Feb 04, 2005 3:37 am Post subject:
Accurately measure C of electrolytic capacitors ? |
|
|
Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
These capacitors are to be used at frequencies
under 1 Hz.
Everytime I try to use my meter to measure, the
capacitance will change from one range scale
to the next, I guess because the frequency changes too.
When I use a typical non-electrolytic capacitor
these changes in readings are not there.
I have been thinking of making
a simple RC inverter oscillator and using
the resulting frequency to determine the
true capacitance in the small signal
application I want to apply them to.
Maybe there are non-electrolytic capacitors
in the 10uf to 100uf range but if so
I have never heard of them before.
I do not know if any of you have ever seen
the SCI FI movie THIS ISLAND EARTH
but I am in need of several of those
fantastic capacitors.
I am trying to get a reading
within 1% of reality.
Help here is appreciated.
--
Regards;
gmv
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|
 |
loedown
Guest
|
| Posted:
Fri Feb 04, 2005 4:26 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
There are non polarized caps, mainly used in loudspeaker crossover networks,
some at 100uF if that helps?
Paul |
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| Back to top |
|
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Rob Gaddi
Guest
|
| Posted:
Fri Feb 04, 2005 4:51 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
Taiyo Yuden as well as several others now makes ceramic caps in the 10uF
to 100 uF range. That said, in small quantity they'll probably hit you
for better than a buck a piece.
Standard aluminum can caps also, IIRC, have a fairly poor temperature
coefficient, and so if you have any substantial currents going through
them you can have drift over that 1% you specced just from self heating.
It's quite possible there are better ways to do whatever you're trying
to do that don't require 1% precision big caps. What's the application?
gmv wrote:
| Quote: | Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
These capacitors are to be used at frequencies
under 1 Hz.
|
....
| Quote: |
Maybe there are non-electrolytic capacitors
in the 10uf to 100uf range but if so
I have never heard of them before.
I do not know if any of you have ever seen
the SCI FI movie THIS ISLAND EARTH
but I am in need of several of those
fantastic capacitors.
I am trying to get a reading
within 1% of reality. |
|
|
| Back to top |
|
|
gmv
Guest
|
| Posted:
Fri Feb 04, 2005 4:54 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
No not just nonpolar but must be also
non-electrolytic.
"loedown" <zero242@internode.on.net> wrote in message news:4202a512$1@duster.adelaide.on.net...
| Quote: | There are non polarized caps, mainly used in loudspeaker crossover networks, some at 100uF if that helps?
Paul
|
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|
| Back to top |
|
|
gmv
Guest
|
| Posted:
Fri Feb 04, 2005 6:19 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
Hello Rob,
I have sent an email to the Yuden people they seem to
have exactly what i need but it is not in a leaded
package I have hopes I can make a leaded cap by soldering
wires on each end of the surface mount type.
The real trouble here is I need the caps to be
closely matched so I am afraid I will have to
buy quite a few just to get a couple to match.
Matching is more important then having the exact value here
because I am making bandpass filters that require
fairly close tolerances.
Another problem is I need only about 30 caps
but they sell them by the zillions.
Why in heck do the US people not carry
non-electrolytic caps in these ranges
of 1uf to 100uf ?
Thanks for your lead on this company.
--
Regards;
gmv
"Rob Gaddi" <rgaddi@bcm.YUMMYSPAMtmc.edu> wrote in message news:ctu9op$nud@gazette.corp.bcm.tmc.edu...
| Quote: | Taiyo Yuden as well as several others now makes ceramic caps in the 10uF to 100 uF range. That said, in small quantity they'll
probably hit you for better than a buck a piece.
Standard aluminum can caps also, IIRC, have a fairly poor temperature coefficient, and so if you have any substantial currents
going through them you can have drift over that 1% you specced just from self heating.
It's quite possible there are better ways to do whatever you're trying to do that don't require 1% precision big caps. What's the
application?
gmv wrote:
Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
These capacitors are to be used at frequencies
under 1 Hz.
...
Maybe there are non-electrolytic capacitors
in the 10uf to 100uf range but if so
I have never heard of them before.
I do not know if any of you have ever seen
the SCI FI movie THIS ISLAND EARTH
but I am in need of several of those
fantastic capacitors.
I am trying to get a reading
within 1% of reality. |
|
|
| Back to top |
|
|
Watson A.Name - \"Watt Su
Guest
|
| Posted:
Fri Feb 04, 2005 2:26 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"gmv" <noemail@please.123> wrote in message
news:JQwMd.18007$C24.14251@attbi_s52...
| Quote: | Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
These capacitors are to be used at frequencies
under 1 Hz.
Everytime I try to use my meter to measure, the
capacitance will change from one range scale
to the next, I guess because the frequency changes too.
When I use a typical non-electrolytic capacitor
these changes in readings are not there.
I have been thinking of making
a simple RC inverter oscillator and using
the resulting frequency to determine the
true capacitance in the small signal
application I want to apply them to.
Maybe there are non-electrolytic capacitors
in the 10uf to 100uf range but if so
I have never heard of them before.
|
Well, there are tantalum caps that are reasonably
sized. But if you use plastic caps, they can be quite
large. I've seen ceiling fan capacitors at the hardware store for a
reasonable price. See this
URL for a wiring diagram (go down to very bottom).
http://home.earthlink.net/~awbrown/fanrepair.htm
You can parallel the two sections for about 10 uF.
You didn't say what the voltage rating of your cap
is. These motor caps may or may not be electrolytic.
But they're really too large. They also have ceiling
fan caps. http://www.action-electronics.com/capac.htm
My guess is that the capacitance of the electrolytic
caps may vary with the applied DC voltage.
| Quote: | I do not know if any of you have ever seen
the SCI FI movie THIS ISLAND EARTH
but I am in need of several of those
fantastic capacitors.
I am trying to get a reading
within 1% of reality.
Help here is appreciated.
--
Regards;
gmv |
|
|
| Back to top |
|
|
Watson A.Name - \"Watt Su
Guest
|
| Posted:
Fri Feb 04, 2005 2:40 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"gmv" <noemail@please.123> wrote in message
news:PczMd.46765$IV5.32350@attbi_s54...
| Quote: | Hello Rob,
I have sent an email to the Yuden people they seem to
have exactly what i need but it is not in a leaded
package I have hopes I can make a leaded cap by soldering
wires on each end of the surface mount type.
The real trouble here is I need the caps to be
closely matched so I am afraid I will have to
buy quite a few just to get a couple to match.
Matching is more important then having the exact value here
because I am making bandpass filters that require
fairly close tolerances.
|
The usual technique is to raise the impedance of the circuit
so that the capacitors can be lower values, below 1 uF. I
realize inductors can get very large and unwieldy, but if you
use RC filters such as twin-T or Wien bridge, the capacitors
can be reasonably sized, below 1 uF.
| Quote: | Another problem is I need only about 30 caps
but they sell them by the zillions.
Why in heck do the US people not carry
non-electrolytic caps in these ranges
of 1uf to 100uf ?
Thanks for your lead on this company.
--
Regards;
gmv
"Rob Gaddi" <rgaddi@bcm.YUMMYSPAMtmc.edu> wrote in message
news:ctu9op$nud@gazette.corp.bcm.tmc.edu...
Taiyo Yuden as well as several others now makes ceramic caps in the
10uF to 100 uF range. That said, in small quantity they'll
probably hit you for better than a buck a piece.
Standard aluminum can caps also, IIRC, have a fairly poor
temperature coefficient, and so if you have any substantial currents
going through them you can have drift over that 1% you specced just
from self heating.
It's quite possible there are better ways to do whatever you're
trying to do that don't require 1% precision big caps. What's the
application?
gmv wrote:
Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
These capacitors are to be used at frequencies
under 1 Hz.
...
Maybe there are non-electrolytic capacitors
in the 10uf to 100uf range but if so
I have never heard of them before.
I do not know if any of you have ever seen
the SCI FI movie THIS ISLAND EARTH
but I am in need of several of those
fantastic capacitors.
I am trying to get a reading
within 1% of reality.
|
|
|
| Back to top |
|
|
loedown
Guest
|
| Posted:
Fri Feb 04, 2005 4:25 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
If you need really closely matched bandpass filters, have you considered
crystal filters. I know very little about them, but I do know they have a
very sharp cutoff / roll off
Paul |
|
| Back to top |
|
|
gmv
Guest
|
| Posted:
Fri Feb 04, 2005 4:38 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in message news:1106d0pdpsb0i35@corp.supernews.com...
| Quote: |
"gmv" <noemail@please.123> wrote in message
news:PczMd.46765$IV5.32350@attbi_s54...
Hello Rob,
I have sent an email to the Yuden people they seem to
have exactly what i need but it is not in a leaded
package I have hopes I can make a leaded cap by soldering
wires on each end of the surface mount type.
The real trouble here is I need the caps to be
closely matched so I am afraid I will have to
buy quite a few just to get a couple to match.
Matching is more important then having the exact value here
because I am making bandpass filters that require
fairly close tolerances.
The usual technique is to raise the impedance of the circuit
so that the capacitors can be lower values, below 1 uF. I
realize inductors can get very large and unwieldy, but if you
use RC filters such as twin-T or Wien bridge, the capacitors
can be reasonably sized, below 1 uF.
|
I would like to keep the resistors as small as I can to
lower the noise they introduce into the system
I am using quite high gain maybe 100 to 105dbv
so that is why I am using large capacitors.
I am amplifying a Geophone signal then feeding
the signal to three different narrow band filters
then summing those three filters into a low pass
filter amplifier for the final run. I am getting
interesting results even though the spice program
indicates terrible phase distortion.
I am fighting terrible noise at my location and
this seems to be the only way to see anything.
Lucky for me different phases of Earthquakes
seem to prefer different frequencies.
But my picture will never be as good as the
big boys.
Just too darn noisy at this location.
I get a terrible noise at maybe 15 Hz or so.
Need to filter like crazy to get rid of it.
It drowns out just about everything i try to do.
I suspect but can not prove that my geophone
is out of spec and not working at the 1Hz
it is supposed to.
The only adjustment I can make is to center the
mass in the housing. If there is a way to lower the
resonant freq I would sure like to know.
I am thinking of finding some weights to put on
the adjustment screw as much weight as can still be
centered.
But it is my experience that for a spring to
lower its frequency it needs to extend or compress
farther in distance. similar to a pendulums length.
T=2PiSqRt(length/gravity)
| Quote: |
Another problem is I need only about 30 caps
but they sell them by the zillions.
Why in heck do the US people not carry
non-electrolytic caps in these ranges
of 1uf to 100uf ?
Thanks for your lead on this company.
--
Regards;
gmv
"Rob Gaddi" <rgaddi@bcm.YUMMYSPAMtmc.edu> wrote in message
news:ctu9op$nud@gazette.corp.bcm.tmc.edu...
Taiyo Yuden as well as several others now makes ceramic caps in the
10uF to 100 uF range. That said, in small quantity they'll
probably hit you for better than a buck a piece.
Standard aluminum can caps also, IIRC, have a fairly poor
temperature coefficient, and so if you have any substantial currents
going through them you can have drift over that 1% you specced just
from self heating.
It's quite possible there are better ways to do whatever you're
trying to do that don't require 1% precision big caps. What's the
application?
gmv wrote:
Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
These capacitors are to be used at frequencies
under 1 Hz.
...
Maybe there are non-electrolytic capacitors
in the 10uf to 100uf range but if so
I have never heard of them before.
I do not know if any of you have ever seen
the SCI FI movie THIS ISLAND EARTH
but I am in need of several of those
fantastic capacitors.
I am trying to get a reading
within 1% of reality.
|
|
|
| Back to top |
|
|
gmv
Guest
|
| Posted:
Fri Feb 04, 2005 4:46 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
They dont work at freqs below 10Hz
unless they are very large.
I have never seen a 1/20Hz crystal before.
"loedown" <zero242@internode.on.net> wrote in message news:42034d8b$1@duster.adelaide.on.net...
| Quote: | If you need really closely matched bandpass filters, have you considered crystal filters. I know very little about them, but I do
know they have a very sharp cutoff / roll off
Paul
|
|
|
| Back to top |
|
|
Watson A.Name - \"Watt Su
Guest
|
| Posted:
Fri Feb 04, 2005 5:22 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"gmv" <noemail@please.123> wrote in message
news:%nIMd.48003$EG1.44889@attbi_s53...
| Quote: | They dont work at freqs below 10Hz
unless they are very large.
I have never seen a 1/20Hz crystal before.
|
You're right, a xtal would have to be huge to get down to that freq.
However you could multiply the low freq many times and then filter it.
| Quote: | "loedown" <zero242@internode.on.net> wrote in message
news:42034d8b$1@duster.adelaide.on.net...
If you need really closely matched bandpass filters, have you
considered crystal filters. I know very little about them, but I do
know they have a very sharp cutoff / roll off
Paul
|
|
|
| Back to top |
|
|
Jim Backus
Guest
|
| Posted:
Fri Feb 04, 2005 8:18 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
On Thu, 3 Feb 2005 21:37:45 UTC, "gmv" <noemail@please.123> wrote:
| Quote: | I am trying to get a reading
within 1% of reality.
I'm not sure reality allows measuring electrolytics to 1% :-) |
I've never considered electrolytics to be stable components. Their
typical manufacturing tolerance is -20% +50%.
--
Jim Backus OS/2 user since 1994
bona fide replies to j <dot> backus <the circle thingy> jita <dot>
demon <dot> co <dot> uk |
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| Back to top |
|
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Rob Gaddi
Guest
|
| Posted:
Sat Feb 05, 2005 12:27 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
While I hate to give my usual answer, have you considered just
digitizing the data and running it through a DSP? You're talking about
some massively slow filters to be trying to make with any reliable
tolerance in analog, and with component values that large it's not going
to be cheap. Plus you can use a linear FIR filter and not have to worry
about the phase distortion you were mentioning.
If your noise is really swamping the signal, and dynamic range is a
concern, at the low speeds you're talking about you could run the signal
through a log amp before you A/D it.
| Quote: |
Lucky for me different phases of Earthquakes
seem to prefer different frequencies.
But my picture will never be as good as the
big boys.
Just too darn noisy at this location.
I get a terrible noise at maybe 15 Hz or so.
Need to filter like crazy to get rid of it.
It drowns out just about everything i try to do.
I suspect but can not prove that my geophone
is out of spec and not working at the 1Hz
it is supposed to.
The only adjustment I can make is to center the
mass in the housing. If there is a way to lower the
resonant freq I would sure like to know.
I am thinking of finding some weights to put on
the adjustment screw as much weight as can still be
centered.
But it is my experience that for a spring to
lower its frequency it needs to extend or compress
farther in distance. similar to a pendulums length.
T=2PiSqRt(length/gravity) |
|
|
| Back to top |
|
|
R.Lewis
Guest
|
| Posted:
Sat Feb 05, 2005 12:33 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"gmv" <noemail@please.123> wrote in message
news:HgIMd.47990$EG1.27201@attbi_s53...
| Quote: |
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:1106d0pdpsb0i35@corp.supernews.com...
"gmv" <noemail@please.123> wrote in message
news:PczMd.46765$IV5.32350@attbi_s54...
Hello Rob,
I have sent an email to the Yuden people they seem to
have exactly what i need but it is not in a leaded
package I have hopes I can make a leaded cap by soldering
wires on each end of the surface mount type.
The real trouble here is I need the caps to be
closely matched so I am afraid I will have to
buy quite a few just to get a couple to match.
Matching is more important then having the exact value here
because I am making bandpass filters that require
fairly close tolerances.
The usual technique is to raise the impedance of the circuit
so that the capacitors can be lower values, below 1 uF. I
realize inductors can get very large and unwieldy, but if you
use RC filters such as twin-T or Wien bridge, the capacitors
can be reasonably sized, below 1 uF.
I would like to keep the resistors as small as I can to
lower the noise they introduce into the system
I am using quite high gain maybe 100 to 105dbv
so that is why I am using large capacitors.
I am amplifying a Geophone signal then feeding
the signal to three different narrow band filters
then summing those three filters into a low pass
filter amplifier for the final run. I am getting
interesting results even though the spice program
indicates terrible phase distortion.
I am fighting terrible noise at my location and
this seems to be the only way to see anything.
Lucky for me different phases of Earthquakes
seem to prefer different frequencies.
But my picture will never be as good as the
big boys.
Just too darn noisy at this location.
I get a terrible noise at maybe 15 Hz or so.
Need to filter like crazy to get rid of it.
It drowns out just about everything i try to do.
I suspect but can not prove that my geophone
is out of spec and not working at the 1Hz
it is supposed to.
The only adjustment I can make is to center the
mass in the housing. If there is a way to lower the
resonant freq I would sure like to know.
I am thinking of finding some weights to put on
the adjustment screw as much weight as can still be
centered.
But it is my experience that for a spring to
lower its frequency it needs to extend or compress
farther in distance. similar to a pendulums length.
T=2PiSqRt(length/gravity)
Another problem is I need only about 30 caps
but they sell them by the zillions.
Why in heck do the US people not carry
non-electrolytic caps in these ranges
of 1uf to 100uf ?
Thanks for your lead on this company.
--
Regards;
gmv
"Rob Gaddi" <rgaddi@bcm.YUMMYSPAMtmc.edu> wrote in message
news:ctu9op$nud@gazette.corp.bcm.tmc.edu...
snip
|
Run it through an A/D to get it into the digital domain where you can handle
it sensibly without having to consider what temperature, sonics, etc will
otherwise do to your filters if you need that sort of accuracy. |
|
| Back to top |
|
|
gmv
Guest
|
| Posted:
Sat Feb 05, 2005 2:05 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
I have a fear in dealing with oscillators
I have no ham license and do not want to
generate more RF energy then currently exists.
I choose to go passive and look only at
baseband signals.
If I wanted to do things right i would
use a capacitive sensor in a kind of
bridge configuration and the capacitor would
FM or AM a carrier frequency
to be later demodulated and amplified.
But like I said there already is too much
RFI and I just do not want to deal with the FCC.
This country might use such an excuse to
throw me back in the nuthouse for the fifth time.
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in message news:1106mgko9mlpiac@corp.supernews.com...
| Quote: |
"gmv" <noemail@please.123> wrote in message
news:%nIMd.48003$EG1.44889@attbi_s53...
They dont work at freqs below 10Hz
unless they are very large.
I have never seen a 1/20Hz crystal before.
You're right, a xtal would have to be huge to get down to that freq.
However you could multiply the low freq many times and then filter it.
"loedown" <zero242@internode.on.net> wrote in message
news:42034d8b$1@duster.adelaide.on.net...
If you need really closely matched bandpass filters, have you
considered crystal filters. I know very little about them, but I do
know they have a very sharp cutoff / roll off
Paul
|
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|
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|
|
|
|
|
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