On May 11, 1:51*am, Jeff Liebermann wrote:
On Mon, 10 May 2010 16:53:58 -0700 (PDT), saber850
wrote:
I'm looking for a cap w/ a lower ESR for the C107 cap (47uF, 50V). *I
don't see 'ESR' in the data sheet. *What do I look for? *
If the ESR isn't specified, then look for loss tangent or dissipation
factor (tan sigma). *Dissipation factor does NOT directly translate to
ESR, but it's proportional when comparing caps at the same frequency.
The lower number is better.
http://en.wikipedia.org/wiki/Dissipation_factor
* ESR = DF / (Pi * freq * C)
You can calculate ESR, but there's a problem. *The dissipation of the
dielectric varies with frequency where the ESR number specified is
only valid at the test frequency. *When DF or loss tangents are
specified, it's sometimes at 120Hz, where the capacitor is intended
for a linear type AC power supply filter. *When ESR is specified, it's
usually at 100KHz which implies that it's for a switching power
supply. *The Panasonic EEU-FC series you included specifies ESR as
impedance at 100KHz. *For comparison, a 47uF/50v Panasonic EEU-FC
series cap as below shows 0.6 ohms max ESR.
Would this
one be better:
http://www.mouser.com/ProductDetail/...70S/?qs=sGAEpi....
Well, for 47uf/50v the Panasonic EEU shows 0.15 DF.
The previous Chemicon KMQ series cap shows 0.12 DF.
I would call the Chemicon capacitor slightly better. *
Unfortunately, the sanity check doesn't quite work. *The ESR at 100KHz
grinds out to:
* ESR = DF * / (2Pi * freq * C)
* ESR = 0.15 / (6.28 * 0.1*10^6 * 47*10^-6)
* ESR = 0.15 / 29.8 = 0.0005
which is about 1000 times too small to be for real. *When my brain
recovers from this cold or flu, I'll try to figure out what I've done
wrong. *(I hate it when that happens).
Most of these caps were near, if not at, the physical size limit. *All
of the 25V caps have = 2mm of space to a neighboring component, and
in 2 cases, it's another cap (so only one could be bigger). *So there
isn't much room for these (one will actually be a very tight fit as
is).
Looking at the photos of the board, some of the caps look fairly
tight. *I guess you should probably leave it at 25V.
--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558
Thanks for all the info.
Which tool(s) should I consider getting to help w/ the desoldering?
I'm guessing there's something to help get the solder out of the PCB
hole. Braided copper? Solder sucker?