How to electronically determine polarity of charged capacito

[Daku]

Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ? Any
hints, suggestions would be helpful.

 

[George Herold]

On Apr 14, 10:33 am, Daku <dakup...@gmail.com> wrote:

Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ? Any
hints, suggestions would be helpful.

A DC voltmeter? Is it over 50 volts?

George H.

 

[Jon Kirwan]

On Thu, 14 Apr 2011 07:52:17 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 14, 10:33 am, Daku <dakup...@gmail.com> wrote:
Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ? Any
hints, suggestions would be helpful.

A DC voltmeter? Is it over 50 volts?

I read it to ask if there was a way to design a meter of some
kind that could let someone attach two leads to an
electrolytic capacitor (or any other type that might also be
polarized) and that it could automatically determine which of
the two leads was (+) and which was (-) so that the operator
could be told, not guess about it.

Perhaps some kind of low voltage leakage test or something
that would monitor the rate of change of capacitance vs
impressed voltage, etc?

Jon

 

[Tom Biasi]

"Jon Kirwan" wrote in message
news:2qoeq6hd9lu48kvhikfpljfn12bfmun98l@4ax.com...

On Thu, 14 Apr 2011 07:52:17 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 14, 10:33 am, Daku <dakup...@gmail.com> wrote:
Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ? Any
hints, suggestions would be helpful.

A DC voltmeter? Is it over 50 volts?

I read it to ask if there was a way to design a meter of some
kind that could let someone attach two leads to an
electrolytic capacitor (or any other type that might also be
polarized) and that it could automatically determine which of
the two leads was (+) and which was (-) so that the operator
could be told, not guess about it.

Perhaps some kind of low voltage leakage test or something
that would monitor the rate of change of capacitance vs
impressed voltage, etc?

Jon

The OP didn't ask about a shelf capacitor, "charged capacitor" was the
question.
DC voltmeter is still the answer.
Tom

 

[Rich Grise]

Jon Kirwan wrote:

On Thu, 14 Apr 2011 07:52:17 -0700 (PDT), George Herold
On Apr 14, 10:33 am, Daku <dakup...@gmail.com> wrote:
Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ? Any
hints, suggestions would be helpful.

A DC voltmeter? Is it over 50 volts?

I read it to ask if there was a way to design a meter of some
kind that could let someone attach two leads to an
electrolytic capacitor (or any other type that might also be
polarized) and that it could automatically determine which of
the two leads was (+) and which was (-) so that the operator
could be told, not guess about it.

Any ordinary DVM will give you this. If the red lead is more negative

than the positive lead, then the display will show a minus sign ('-')
at the left end of the digits. (and, of course, the digits will tell
you how many volts the DUT is charged to.)

Hope This Helps!
Rich

 

[Rich Grise]

Daku wrote:

Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ? Any
hints, suggestions would be helpful.

So, do you ever plan to come back to look for answers, or are you waiting
for the answer fairy to leave them under your pillow?

Thanks,
Rich

 

[whit3rd]

On Thursday, April 14, 2011 2:15:36 PM UTC-7, Jon Kirwan wrote:

On Thu, 14 Apr 2011 07:52:17 -0700 (PDT), George Herold
ghe...@teachspin.com> wrote:

On Apr 14, 10:33�am, Daku <daku...@gmail.com> wrote:
Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ?

I read it to ask if there was a way to design a meter of some
kind that could let someone attach two leads to an
electrolytic capacitor (or any other type that might also be
polarized) and that it could automatically determine which of
the two leads was (+) and which was (-)

Yes, that makes more sense; instead of 'a charged capacitor'
it would be 'a poled electrolytic capacitor'.

There's one way: the leakage should be greater in the 'wrong'
direction, so an AC source (transformer-coupled, you cannot
allow any DC for this) connected to the capacitor, and a good
DC meter, should show you the 'right' polarity.

 

[George Herold]

On Apr 14, 5:15 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

On Thu, 14 Apr 2011 07:52:17 -0700 (PDT), George Herold

gher...@teachspin.com> wrote:
On Apr 14, 10:33 am, Daku <dakup...@gmail.com> wrote:
Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ? Any
hints, suggestions would be helpful.

A DC voltmeter?  Is it over 50 volts?

I read it to ask if there was a way to design a meter of some
kind that could let someone attach two leads to an
electrolytic capacitor (or any other type that might also be
polarized) and that it could automatically determine which of
the two leads was (+) and which was (-) so that the operator
could be told, not guess about it.

Perhaps some kind of low voltage leakage test or something
that would monitor the rate of change of capacitance vs
impressed voltage, etc?

Jon

Geesh, OK you can read whatever you like into the question. But it's
easy to determine the polarity of a "charged capacitor".
I think I'm starting to sound like Phil A. Pretty soon I'll be
cussing like a banshee.

George H.

 

[Rich Grise]

Daku top-posted:

On Apr 14, 6:27 pm, Rich Grise <ri...@example.net.invalid> wrote:

So, do you ever plan to come back to look for answers, or are you waiting
for the answer fairy to leave them under your pillow?

[top-post repaired]
Thanks for each of your responses. In my original post,
when I said "electronically" what I had in mind was an
in-circuit automated sub-circuit that would periodically
check the plate polarities of a capacitor, and set a flag,
for example depending on the polarity of a specified plate.
I mean, the capacitor might be getting charged/discharged
by some unknown waveform, and all we want is to know
the polarity of a specified plate at periodic intervals.

I wish there was an answer fairy. Then, I could ask the
question at night before going to sleep, and next morning,
lo and behold there is sheet of paper stuck under my
pillow with the right answer.

Yes, of course. Just use any differential-input bipolar ADC,

that your software can read at its leisure.

And don't top post, and try to get off google; this is USENET,
not "google groups." Preferably, get a real news server - your
ISP might offer one; I use eternal-september.org - and a real
news reader program.

Good Luck!
Rich

 

[Daku]

Thanks for each of your responses. In my original post,
when I said "electronically" what I had in mind was an
in-circuit automated sub-circuit that would periodically
check the plate polarities of a capacitor, and set a flag,
for example depending on the polarity of a specified plate.
I mean, the capacitor might be getting charged/discharged
by some unknown waveform, and all we want is to know
the polarity of a specified plate at periodic intervals.

I wish there was an answer fairy. Then, I could ask the
question at night before going to sleep, and next morning,
lo and behold there is sheet of paper stuck under my
pillow with the right answer.

On Apr 14, 6:27 pm, Rich Grise <ri...@example.net.invalid> wrote:

So, do you ever plan to come back to look for answers, or are you waiting
for the answer fairy to leave them under your pillow?

Thanks,
Rich

 

[John Fields]

On Thu, 14 Apr 2011 20:53:23 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 14, 5:15 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
On Thu, 14 Apr 2011 07:52:17 -0700 (PDT), George Herold

gher...@teachspin.com> wrote:
On Apr 14, 10:33 am, Daku <dakup...@gmail.com> wrote:
Could some electronics guru please help ? How would one electronically
determine the polarity of the plates of a charged capacitor ? Any
hints, suggestions would be helpful.

A DC voltmeter?  Is it over 50 volts?

I read it to ask if there was a way to design a meter of some
kind that could let someone attach two leads to an
electrolytic capacitor (or any other type that might also be
polarized) and that it could automatically determine which of
the two leads was (+) and which was (-) so that the operator
could be told, not guess about it.

Perhaps some kind of low voltage leakage test or something
that would monitor the rate of change of capacitance vs
impressed voltage, etc?

Jon

Geesh, OK you can read whatever you like into the question. But it's
easy to determine the polarity of a "charged capacitor".
I think I'm starting to sound like Phil A. Pretty soon I'll be
cussing like a banshee.

George H.

---
Banshees don't cuss, they wail.

http://en.wikipedia.org/wiki/Banshee
--
JF

 

[ehsjr]

Daku wrote:

Thanks for each of your responses. In my original post,
when I said "electronically" what I had in mind was an
in-circuit automated sub-circuit that would periodically
check the plate polarities of a capacitor, and set a flag,
for example depending on the polarity of a specified plate.
I mean, the capacitor might be getting charged/discharged
by some unknown waveform, and all we want is to know
the polarity of a specified plate at periodic intervals.

Use a comparator with one input connected to the specified
plate of the cap, and the other input connected to the
reference voltage. The comparator output will change from high
to low (or low to high) whenever the plate of the cap changes
polarity, even if the plate is only slightly above or slightly
below the reference. You can poll that flag at whatever intervals
you need - the flag will always indicate the polarity per your
definition. You'll also need to define what happens in response
to the flag when it is polled - does an LED light, does an alarm
sound, does some other sub-circuit get reset, whatever.

If you need a range of voltage, use a window comparator. Your
definition of polarity determines both the reference voltage
level, and the range. For example, you might call anything
above 3 volts positive, and anything below 2.5 volts negative.

Ed

I wish there was an answer fairy. Then, I could ask the
question at night before going to sleep, and next morning,
lo and behold there is sheet of paper stuck under my
pillow with the right answer.

On Apr 14, 6:27 pm, Rich Grise <ri...@example.net.invalid> wrote:

So, do you ever plan to come back to look for answers, or are you waiting
for the answer fairy to leave them under your pillow?

Thanks,
Rich