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On Tue, 25 Jan 2011 14:58:37 +1100, Phil Allison wrote:
** Anyone who needs to check the ESR of a few electros can lash up a
test
rig in seconds - all you need is a bench audio generator and a basic
scope or CRO as poms and Aussies call them.
Set the audio gen to about 100kHz
My Leader audio generator doesn't do 100kHz. What 'audio generator' does?
Thanks for the clarification. I suspected something like that, but didn't** Connection of the scope direct to the electro cap is important.
Otherwise, the inductive reactance of the cable from the generator
( at 100kHz ) to the cap becomes included in the scope display of
ESR - and is often more than the ESR of a good cap.
In other words... If the driving frequency is high enough that theLong as you connect the scope direct to the leads of the
electro and know the current level from the generator --
actual ESR values can be found.
** Errr - yep.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?
Since Phil is comparing impedance values and not component values,A 0.1uF ceramic has an impedance of 16 ohms at 100KHz  -  while a
typical 100uF electro has an impedance of 0.16 ohms at 100kHz. That
is 100 times less !!!
Can't argue with facts.
Nice tip thanks Phil. The 100uF electro's I have came out with ~0.15"William Sommerwerck"
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.
..... Phil
Nice tip thanks Phil. The 100uF electro's I have came out with ~0.15In 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.
That's great! Thanks Phil, I found some graphs by Vishay, but they"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/Web/Sections/ProductCatalog/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
Perhaps you've stumbled onto the "anti-capacitor". Maybe you couldI 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.)
Hmm, Well I was thinking about this. Perhaps the RCL meter looks atOn 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.