How to test 1F Capacitors ?

W

WMGS

Guest
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS
 
WMGS wrote:
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS
Click to expand...
Why do you want to check them???

If you're building something, what cap parameters are important to that
design? Test for that.

If you just want to verify that they meet their spec, the first thing
you have to do is obtain and understand that spec. Then you have to
devise a test for each spec. And you probably need to heat them real
hot and cool them real cold to verify the electrical specs over the
specified temperature range.

Bottom line is that it's probably not practical. Just decide what's
most important and test that.
If "lots" is 50 your problem is different than if "lots" is 500,000 units.
mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
You can build and simple RC Circuit and measure the time constant in
charging or discharging.

Al

"WMGS" <98901118R@polyu.edu.hk> wrote in message
news:74ecc3cb.0309212210.68a13588@posting.google.com...
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS
Click to expand...
 
Find a Wheatstone (sp?) Bridge circuit. You can compare two items
(coils, capacitors, resistors) depending on the construction. I think
the ancient Heathkit Capacitor Meter (tubes!) had that feature.

Otherwise you need to look for some rather rare Capacitor test
equipment.

John :-#)#

On 21 Sep 2003 23:10:38 -0700, 98901118R@polyu.edu.hk (WMGS) wrote:

Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS
Click to expand...
(Please post followups or tech enquires to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
 
"WMGS" <98901118R@polyu.edu.hk> wrote in message
news:74ecc3cb.0309212210.68a13588@posting.google.com...
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS
Click to expand...
Just as another poster sez. Charge them up to their rated voltage, then
discharge them through a 1k resistor. They will discharge to 1/2 their rated
voltage in 693 seconds if they are really 1F, and if the resistor is really
1k.

Regards,
Bob Monsen
 
"WMGS" <98901118R@polyu.edu.hk> wrote in message
news:74ecc3cb.0309212210.68a13588@posting.google.com...
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS
Click to expand...
What is it that you want to check?
Capacitance, leakage, deltaC vs lots of things etc etc.
 
In article <74ecc3cb.0309212210.68a13588@posting.google.com>,
98901118R@polyu.edu.hk mentioned...
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS
Click to expand...
The cap is so large in capacitance that you can just charge it up to
2.5V if that's its rated V, and then put a load resistor across the
cap, and watch the voltage on a digital voltmeter. With a 100 ohm
resistor, the voltage should take 1 TC (time constant) to discharge
down to 36% of 2.5V, or .9V, in 100 seconds. That might get a bit
snoring boring, so reduce the resistance to a lower and hence more
hasty value. Use three 100 ohm in parallel or a 33 ohm resistor for
33 seconds.

I just tried it twice with a 39 ohm resistor and it took 37 seconds.
I used a constant current PS at 200 mA to charge the cap. So the
theory is confirmed experimentally. ;-)


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
In article <3F6EBE7B.9060201@juno.com>, spamme0@juno.com mentioned...
WMGS wrote:
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS

Why do you want to check them???

If you're building something, what cap parameters are important to that
design? Test for that.

If you just want to verify that they meet their spec, the first thing
you have to do is obtain and understand that spec. Then you have to
devise a test for each spec. And you probably need to heat them real
hot and cool them real cold to verify the electrical specs over the
specified temperature range.

Bottom line is that it's probably not practical.
Click to expand...
No, what _you_ are telling him is not practical. That's the bottom
line. See my other followup for a simple and easy way to check them.

Just decide what's
most important and test that.
If "lots" is 50 your problem is different than if "lots" is 500,000 units.
mike
Click to expand...

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
In article <7l9umvge3id3fcfpnl0o9acc84816tjqos@4ax.com>,
jrr@flippers.com mentioned...
Find a Wheatstone (sp?) Bridge circuit. You can compare two items
(coils, capacitors, resistors) depending on the construction. I think
the ancient Heathkit Capacitor Meter (tubes!) had that feature.

Otherwise you need to look for some rather rare Capacitor test
equipment.

John :-#)#
Click to expand...
Nonsense! See my followup.


On 21 Sep 2003 23:10:38 -0700, 98901118R@polyu.edu.hk (WMGS) wrote:

Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS
Click to expand...

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
In article <lpKbb.548107$Ho3.95502@sccrnsc03>,
postmaster@BulkingPro.com mentioned...
"WMGS" <98901118R@polyu.edu.hk> wrote in message
news:74ecc3cb.0309212210.68a13588@posting.google.com...
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS

Just as another poster sez. Charge them up to their rated voltage, then
discharge them through a 1k resistor. They will discharge to 1/2 their rated
voltage in 693 seconds if they are really 1F, and if the resistor is really
1k.

Regards,
Bob Monsen
Click to expand...
You think anyone wants to wait 11 minutes and 33 seconds? Boooooring!
Try a 100 ohm resistor instead.



--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
Watson A.Name - Watt Sun wrote:
In article <3F6EBE7B.9060201@juno.com>, spamme0@juno.com mentioned...

WMGS wrote:

Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS

Why do you want to check them???

If you're building something, what cap parameters are important to that
design? Test for that.

If you just want to verify that they meet their spec, the first thing
you have to do is obtain and understand that spec. Then you have to
devise a test for each spec. And you probably need to heat them real
hot and cool them real cold to verify the electrical specs over the
specified temperature range.

Bottom line is that it's probably not practical.


No, what _you_ are telling him is not practical. That's the bottom
line. See my other followup for a simple and easy way to check them.
Click to expand...
I musta missed your post. Please post it again.
All I saw from you was a way to get an approximate value for the
capacitance by timing a low current discharge. That's hardly what the
OP asked, "want to check them if they are up to
their claimed stsndard." In almost all the applications I can think
of, leakage or ESR might be CRITICAL parameters. I don't know the
failure mode for over voltage, but if they're surplus, that might also
be a thing to test for.

This brings up two of my pet peeves:

1)people don't ask the question they want the answer to.
Often they don't even know what to ask. An "overkill"
answer at least gives them a framework to hang more questions on.
(ending sentences with prepositions is not an error...it's a skill)

2)Very smart and experienced people make grand assumptions about what
the OP meant and launch into specific solutions. (Maybe I'd do better if
I put the psychic hotline on speed dial...)
Then they defend their position against more open-minded discussion.

One of the greatest impediments to communication is believing that you
understood the other's position.

A lot of this could be avoided if people would talk a little about their
application when they ask vague questions.

mike

Just decide what's
most important and test that.
If "lots" is 50 your problem is different than if "lots" is 500,000 units.
mike
Click to expand...


--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
Would a 1F cap charged to 1V discharged thru 1 ohm
measure 1A for 1 sec?
Sounds like something I have heard before a long, long
time ago in a place far.....
Jeff


"Watson A.Name - Watt Sun" <alondra101@hotmail.com> wrote in message
news:MPG.19d9c395e9b2f1fa9896ea@news.dslextreme.com...
In article <74ecc3cb.0309212210.68a13588@posting.google.com>,
98901118R@polyu.edu.hk mentioned...
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS

The cap is so large in capacitance that you can just charge it up to
2.5V if that's its rated V, and then put a load resistor across the
cap, and watch the voltage on a digital voltmeter. With a 100 ohm
resistor, the voltage should take 1 TC (time constant) to discharge
down to 36% of 2.5V, or .9V, in 100 seconds. That might get a bit
snoring boring, so reduce the resistance to a lower and hence more
hasty value. Use three 100 ohm in parallel or a 33 ohm resistor for
33 seconds.

I just tried it twice with a 39 ohm resistor and it took 37 seconds.
I used a constant current PS at 200 mA to charge the cap. So the
theory is confirmed experimentally. ;-)


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
Click to expand...
 
"Jeff" <frontline_electronics@NSatt.net> wrote in message
news:rA4cb.156255$3o3.11148081@bgtnsc05-news.ops.worldnet.att.net...
Would a 1F cap charged to 1V discharged thru 1 ohm
measure 1A for 1 sec?
Sounds like something I have heard before a long, long
time ago in a place far.....
Jeff
Click to expand...
No, it would not. Think about it. If you start out with the cap at 1V, and
you put a 1R resistor in parallel, then 1A starts flowing through the
circuit. But that starts the cap to discharging, so the voltage drops. So
then there's less voltage across the resistor, so the current drops too, so
the rate of discharge drops. The end result is that the discharge is
exponential, if the resistance is constant.

Another way is to vary the resistance, so that the discharge *current* is
constant. Then the voltage decline will be constant: dV/dT = I*C. So if a
1F cap is discharged at a constant 1A, it will discharge at 1v/second,
meaning it will go from 1v to 0v in 1 second. But to do that you have to be
changing the resistance from 1 ohm at the beginning, down to
(asymptotically) 0 ohms at the end.
 
In article <3F70B5F7.6080305@juno.com>, spamme0@juno.com mentioned...
Watson A.Name - Watt Sun wrote:
In article <3F6EBE7B.9060201@juno.com>, spamme0@juno.com mentioned...

WMGS wrote:

Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS

Why do you want to check them???

If you're building something, what cap parameters are important to that
design? Test for that.

If you just want to verify that they meet their spec, the first thing
you have to do is obtain and understand that spec. Then you have to
devise a test for each spec. And you probably need to heat them real
hot and cool them real cold to verify the electrical specs over the
specified temperature range.

Bottom line is that it's probably not practical.


No, what _you_ are telling him is not practical. That's the bottom
line. See my other followup for a simple and easy way to check them.

I musta missed your post. Please post it again.
All I saw from you was a way to get an approximate value for the
capacitance by timing a low current discharge. That's hardly what the
OP asked, "want to check them if they are up to
their claimed stsndard." In almost all the applications I can think
of, leakage or ESR might be CRITICAL parameters. I don't know the
failure mode for over voltage, but if they're surplus, that might also
be a thing to test for.

This brings up two of my pet peeves:

1)people don't ask the question they want the answer to.
Often they don't even know what to ask. An "overkill"
answer at least gives them a framework to hang more questions on.
(ending sentences with prepositions is not an error...it's a skill)
Click to expand...
I interpreted his statement "I know it is common to check "u"F
Capacitors but not 1F " as meaning he wanted to know the value of the
capacitance. As would apply to most electrolytics, the method I gave
was good enough to measure that value to well within the usual 20 or
more percent of the average electrolytic. Using a 100 ohm resistor
for 100 seconds would give even more accuracy when using a stopwatch
or sweep second, but it might become just a bit tedious waiting over a
minute and a half for a result.

2)Very smart and experienced people make grand assumptions about what
the OP meant and launch into specific solutions. (Maybe I'd do better if
I put the psychic hotline on speed dial...)
Then they defend their position against more open-minded discussion.

One of the greatest impediments to communication is believing that you
understood the other's position.

A lot of this could be avoided if people would talk a little about their
application when they ask vague questions.
Click to expand...
That usually happens in the followup discussion after the original
post. There would be no need for discussion, if that didn't occur.
In that case, just go do a search for the FAQ on the subject.

mike


Just decide what's
most important and test that.
If "lots" is 50 your problem is different than if "lots" is 500,000 units.
mike
Click to expand...

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
In article <rA4cb.156255$3o3.11148081@bgtnsc05-
news.ops.worldnet.att.net>, frontline_electronics@NSatt.net
mentioned...
Would a 1F cap charged to 1V discharged thru 1 ohm
measure 1A for 1 sec?
Sounds like something I have heard before a long, long
time ago in a place far.....
Jeff
Click to expand...
It would, assuming that the internal series resistance of the cap was
zero. But it isn't. So you should dischrge the cap at a rate where
the ESR is small in relation to the discharge resistance.


"Watson A.Name - Watt Sun" <alondra101@hotmail.com> wrote in message
news:MPG.19d9c395e9b2f1fa9896ea@news.dslextreme.com...
In article <74ecc3cb.0309212210.68a13588@posting.google.com>,
98901118R@polyu.edu.hk mentioned...
Dear All,

I have lots of 1F Capacitors and want to check them if they are up to
their claimed stsndard. What should I do ? What equipment should I
need and where to find them ? I know it is common to check "u"F
Capacitors but not 1F .

Thanks in advance
WMGS

The cap is so large in capacitance that you can just charge it up to
2.5V if that's its rated V, and then put a load resistor across the
cap, and watch the voltage on a digital voltmeter. With a 100 ohm
resistor, the voltage should take 1 TC (time constant) to discharge
down to 36% of 2.5V, or .9V, in 100 seconds. That might get a bit
snoring boring, so reduce the resistance to a lower and hence more
hasty value. Use three 100 ohm in parallel or a 33 ohm resistor for
33 seconds.

I just tried it twice with a 39 ohm resistor and it took 37 seconds.
I used a constant current PS at 200 mA to charge the cap. So the
theory is confirmed experimentally. ;-)


--
Click to expand...

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
"Watson A.Name - Watt Sun" <alondra101@hotmail.com> wrote in message
news:MPG.19dacb8715d389199896f7@news.dslextreme.com...
In article <rA4cb.156255$3o3.11148081@bgtnsc05-
news.ops.worldnet.att.net>, frontline_electronics@NSatt.net
mentioned...
Would a 1F cap charged to 1V discharged thru 1 ohm
measure 1A for 1 sec?
Sounds like something I have heard before a long, long
time ago in a place far.....
Jeff

It would, assuming that the internal series resistance of the cap was
zero. But it isn't. So you should dischrge the cap at a rate where
the ESR is small in relation to the discharge resistance.
Click to expand...
It wouldn't - Watson, you're not thinking about your math here. See my
other posting.

But the point you're making is a good one. My posting described an ideal
cap, but at least some of the very-large-value caps out there (e.g., gold
caps) have got very high internal resistance. If you try to discharge them
at high current, most of the juice gets wasted in heating up the cap.
 
In article <bkre73$r9f$0@216.39.172.65>, walterh@cafewalterNOSPAM.com
mentioned...
"Watson A.Name - Watt Sun" <alondra101@hotmail.com> wrote in message
news:MPG.19dacb8715d389199896f7@news.dslextreme.com...
In article <rA4cb.156255$3o3.11148081@bgtnsc05-
news.ops.worldnet.att.net>, frontline_electronics@NSatt.net
mentioned...
Would a 1F cap charged to 1V discharged thru 1 ohm
measure 1A for 1 sec?
Sounds like something I have heard before a long, long
time ago in a place far.....
Jeff

It would, assuming that the internal series resistance of the cap was
zero. But it isn't. So you should dischrge the cap at a rate where
the ESR is small in relation to the discharge resistance.

It wouldn't - Watson, you're not thinking about your math here. See my
other posting.

But the point you're making is a good one. My posting described an ideal
cap, but at least some of the very-large-value caps out there (e.g., gold
caps) have got very high internal resistance. If you try to discharge them
at high current, most of the juice gets wasted in heating up the cap.
Click to expand...
Yeah, it would (ideally) be 1 A only initially, as the other followup
said. My mistake.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote in message
news:vn1maknggf9eb7@corp.supernews.com...
"Jeff" <frontline_electronics@NSatt.net> wrote in message
news:rA4cb.156255$3o3.11148081@bgtnsc05-news.ops.worldnet.att.net...
Would a 1F cap charged to 1V discharged thru 1 ohm
measure 1A for 1 sec?
Sounds like something I have heard before a long, long
time ago in a place far.....
Jeff

No, it would not. Think about it. If you start out with the cap at 1V,
and
you put a 1R resistor in parallel, then 1A starts flowing through the
circuit. But that starts the cap to discharging, so the voltage drops.
So
then there's less voltage across the resistor, so the current drops too,
so
the rate of discharge drops. The end result is that the discharge is
exponential, if the resistance is constant.

Another way is to vary the resistance, so that the discharge *current* is
constant. Then the voltage decline will be constant: dV/dT = I*C.
Click to expand...
oops .... dV/dt is not = I*C for a capacitor


So if a
1F cap is discharged at a constant 1A, it will discharge at 1v/second,
meaning it will go from 1v to 0v in 1 second. But to do that you have to
be
changing the resistance from 1 ohm at the beginning, down to
(asymptotically) 0 ohms at the end.
Click to expand...
 
"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:bksqb8$hr4$1@thorium.cix.co.uk...
oops .... dV/dt is not = I*C for a capacitor
Click to expand...
Sorry, you're right. dV/dt = I/C. (Bigger cap means same current charges
it more slowly. Duh.)

Same answer, though, in this case :)
 
"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote in message
news:vn1maknggf9eb7@corp.supernews.com...
"Jeff" <frontline_electronics@NSatt.net> wrote in message
news:rA4cb.156255$3o3.11148081@bgtnsc05-news.ops.worldnet.att.net...
Would a 1F cap charged to 1V discharged thru 1 ohm
measure 1A for 1 sec?
Sounds like something I have heard before a long, long
time ago in a place far.....
Jeff

No, it would not. Think about it. If you start out with the cap at 1V,
and
you put a 1R resistor in parallel, then 1A starts flowing through the
circuit. But that starts the cap to discharging, so the voltage drops.
So
then there's less voltage across the resistor, so the current drops too,
so
the rate of discharge drops. The end result is that the discharge is
exponential, if the resistance is constant.

Another way is to vary the resistance, so that the discharge *current* is
constant. Then the voltage decline will be constant: dV/dT = I*C. So if
a
1F cap is discharged at a constant 1A, it will discharge at 1v/second,
meaning it will go from 1v to 0v in 1 second. But to do that you have to
be
changing the resistance from 1 ohm at the beginning, down to
(asymptotically) 0 ohms at the end.
Click to expand...
Of course the meter responce should be included in
the measurement/time.
I have never tried that measurement and do not know
how my meter would read but I would assume 1A
for a short time and then not much because it would
be over by then.
Just joking on the "question" but maybe a peak hold
function would give a faster answer to the OP.
Jeff
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top