On Jan 26, 10:28*pm, "Phil Allison" wrote:
"George Herold is a real Pain "



In other words... If the driving frequency is high enough that the
capacitive reactance is essentially zero, then the net impedance is
essentially the ESR. Right?

** Errr - yep.

But it ain't that simple.

One has to examine the actual impedance curves for typical electros to see
what the game is - the curve is like no other kind of cap.

Think of Q factors of circa 0.05 and ESRs that way exceed the calculated
impedance at 100kHz.

Nice tip thanks Phil. *The 100uF electro's I have came out with ~0.15
ohms of ESR, using your method.
I've never seen an impedance curve for an electro cap. *Do you have a
link or know which manufacturer's website I might check?

** Found this PDF on the net *- seems to have lots good info on the humble
electro.

http://www.epcos.com/web/generator/W...Catalog/Capaci...

See page 15, *figs 13 and 14.

One can easily see the dramatic effect temperature has on the impedance
minima or ESR *- *electros work better when they are HOT !!

Also, the minimum impedance value ( same as the ESR ) occurs around 50 -
100kHz and is quite broad - the *higher the ESR and the lower the temp the
broader.

At 20C the 47uF, 350 volt electro in fig 14 exhibits a deep impedance minima
( essentially 0.4 ohms resistive ) from 10kHz to 2 MHz.

.... *Phil

That's great! Thanks Phil, I found some graphs by Vishay, but they
weren't nearly as nice. (No temperature dependence and frequencies
only to 100kHz) Of course at high temperatures the electro's leak
more.

I used your techinque to look at a 1000uF cap. I used a DSO with a
bit of signal averaging. ('scope triggered from a sync output from the
generator) I got something like 0.016 ohms at 100kHz. Our SRS RCL
meter measured 0.014 ohms at 10kHz for the same cap. and then 'lost
it's mind' at 100kHz. (reported a negative capacitance.)

George H.

On 1/27/2011 7:06 AM George Herold spake thus:

I used your techinque to look at a 1000uF cap. I used a DSO with a
bit of signal averaging. ('scope triggered from a sync output from the
generator) I got something like 0.016 ohms at 100kHz. Our SRS RCL
meter measured 0.014 ohms at 10kHz for the same cap. and then 'lost
it's mind' at 100kHz. (reported a negative capacitance.)

Perhaps you've stumbled onto the "anti-capacitor". Maybe you could
patent it ...


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

On Jan 28, 12:28*am, David Nebenzahl wrote:
On 1/27/2011 7:06 AM George Herold spake thus:

I used your techinque to look at a 1000uF cap. *I used a DSO with a
bit of signal averaging. ('scope triggered from a sync output from the
generator) *I got something like 0.016 ohms at 100kHz. *Our SRS RCL
meter measured 0.014 ohms at 10kHz for the same cap. *and then 'lost
it's mind' at 100kHz. *(reported a negative capacitance.)

Perhaps you've stumbled onto the "anti-capacitor". Maybe you could
patent it ...

--
Comment on quaint Usenet customs, from Usenet:

* *To me, the *plonk...* reminds me of the old man at the public hearing
* *who stands to make his point, then removes his hearing aid as a sign
* *that he is not going to hear any rebuttals.

Hmm, Well I was thinking about this. Perhaps the RCL meter looks at
the phase shift to get the sign. The minus sign would indicate that
at 100kHz the 1000uF cap has passed through it's minimum impedance
point and is now rising up the other side and looking more inductive
to the driver.

(Just a guess.)
George H.