On Wed, 10 Oct 2012, Stefan Trethan wrote:
That explains that then, they measure a few percent lower at 1kHz.
It's unfair to accuse a manufacturer of penny pinching if you don't
meet their specified testing conditions (usually 120Hz).
It gives same readings at 120Hz for capacitance if it can measure it
(>100uF). For 10-100uF range the most accurate results are at 400 Hz. 1KHz
is a convenient test frequency giving wide range with relatively good
accuracy. It might give up to 3% error at the boundary F/C ranges where it
barely measures capacitance (too high F for big C or too low F for small C)
but it is never 20%. If you want to get most of it, sure you have to choose
a proper frequency. But for 3 digits 1KHz is good for measuring almost
anything. Also capacitance itself does not vary that much with frequency.
ESR varies orders of magnitude more.
Saving a few percent of foil is probably not worth the hassle of
having to meet tighter tolerances caused by leaning towards the lower
end. More likely they used to go above nominal with the old caps
It does. And almost all big manufacturers has shown tendency towards saving
a penny risking a buck. It doesn't make sense in a long run but who thinks
farther than a quarter? Does it make sense to lay off the best (those with
highest salaries) to make a nice profit figure? Can you name a company that
did not fell to a temptation of using cheaper chinese capacitors in high
frequency high ripple applications and thus avoided massive failures because
of blown capacitors? Remember, profit of saving a penny is now and this is
when the higher management gets their bonuses for making profit. Failures
are later and they are not punished for those. And no one of them is going
to work for a particular company forever -- they will go to a different one
for making that one more profitable too once they are done with their
current one (i.e. once it is destroyed by making it more profitable.)
because tolerances were asymmetrical back then.
Nope. Old ones usually fall in the middle of their tolerance range. If it
was +80/-20% the majority of 1,000uF capacitors had 1,300uF capacitance. And
even +/-20% ones rarely went under 100%. It was also understood that it is
better to overshoot than undershoot as far as capacitance goes.
I'll check out the test data to see if the distribution is offset when
I get the chance.
ST
On Wed, Oct 10, 2012 at 10:23 PM, Sergey Kubushyn <ksi@...> wrote:
On Wed, 10 Oct 2012, Stefan Trethan wrote:
At 1kHz that's just about spot on specification for the taiyo yuden part.
The impedance at this frequency will be what, 15, 16 Ohms? Not sure
why you'd worry....
I do not worry. It is not about using it at a particular frequency.
At what frequency did you measure capacitance? Just so that we don't
waste both our time again.
1KHz. And I don't have time to waste too.
ST
On Wed, Oct 10, 2012 at 9:22 PM, Sergey Kubushyn <ksi@...> wrote:
On Wed, 10 Oct 2012, Stefan Trethan wrote:
On Wed, Oct 10, 2012 at 6:59 PM, Sergey Kubushyn <ksi@...> wrote:
There were bunch of 10uF 25V ones
that I was going to replace with 1206 SMD X5R ceramics but to my surprise
those dipped tantalums had something like 300mOhm ESR that is actually
BETTER than ceramics (Taiyo Yuden 10uF 25V 1206 X5R ceramics of recent
manufacturing that I had several reels in my parts bins have something like
350mOhms ESR.)
At what frequency? The ceramic should have well below 10mR at 100kHz
according to specification, and I just don't see how it could be
otherwise considering the construction.
1KHz. This is actual measured values. As for the specifications majority of
manufacturers don't give any values on ESR in their datasheets. It is
"common knowledge" they are "very low ESR" but reality check shows totally
different picture. If you look at e.g. NIC NMC High CV Series datasheet (one
of the few who give data on ESR) you'll see a ESR vs Frequency chart. It
clearly shows that MLCCs are better when going into MHz range but they are
nothing to write home about at lower frequencies.
Regarding the generally low capacitance value on electrolytics, I have
extensive test data for Rubycon and Nippon Chemicon at work and will
check if they are consistently at the lower capacitance tolerance.
Once again, I do NOT have very extensive data, just several hundred
capacitors. It might be not a representative sample but I could not find a
SINGLE one of recent manufacturing that was 100% of stated capacity or
higher. On the old ones I could not find more than couple of pieces that
were under 100%.
ST
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