[time-nuts] GC-1000 Clock Cap Choice?
Dr. Frank Stellmach
drfrank.stellmach at freenet.de
Sun Jan 16 21:58:49 UTC 2011
Our electronics designers (@automotive electronics supplier) have to
take lot of care concerning voltage stabilizers, that the cap provides
sufficiently low ESR, which electrolytics deliver only at much higher
capacitance value; and a series resistor is introduced to limit loading
currents of the Tantalum. Otherwise, the Tantalums might fail, either
open, or they might burn, which already caused total damage of vehicles
I assume, latter aspect has been overseen in your device. This is the
main fault modus of Tantalums.
Electrolytics dry out over the years, especially when stored
non-operating, Tantalums do not at all.
You have to chose higher cap value and higher environmental temperature
grade (>= 105°C) for the ElCo, to get a reliable replacement.
I commonly do not recommend polymer elcos, they have some further
disadvantages, one being the price, the other (perhaps) being CN
compounds in the polymer, which may be poisonous in case of fire.
High cap value Ceramics are available since years, therefore , if price
is no argument, I'd prefer to take them for values up to ~ 100µF; X5R
ceramics should be good enough. With some luck, they (SMD type) fit to
the existing pads on the solder side.
Otherwise, you have to analyse the (misdesigned) circuitry for possible
high pulse currents, and replace the bad tantalums by new ones in series
with a limiting resistor. Several tantalums in parallel might also
improve withstanding to current pulses. Check the tantalums datasheets.
epcos has got some detailed application hints, as far as I remember.
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