12
EPCOS AG
Product safety
Polarity
Make sure that polar capacitors are
connected with the right polarity. If
the opposite polarity were to be ap-
plied, this would cause an electrolyt-
ic process resulting in the formation
of a dielectric layer on the cathode
foil. In this case strong internal heat
generation and gas emission may
occur and destroy the capacitor.
Polar capacitors do not tolerate a
voltage reversal. Incorrect polarities
of up to 1.5 V are, however, permis-
sible for short periods of time as the
formation of a damaging oxide layer
on the cathode only starts at volt-
ages of this magnitude.
Reverse voltage
Aluminum electrolytic capacitors are
polar capacitors. Where necessary,
voltages of opposite polarity should
be prevented by connecting a
diode. The diode’s conducting-state
voltage of approximately 0.8 V is
permissible. Reverse voltages ≤1.5 V
are tolerable for a duration of less
than 1 second, but not in continu-
ous or repetitive operation.
Breakdown strength of
insulating sleeves
The minimum breakdown strength of
the insulating sleeve is 2500 VAC or
3500 VDC. A test method for verifying
the breakdown strength of the slee-
ves is described in IEC 60384-4.
In order to ensure full breakdown
strength, care must be taken not to
damage the insulating sleeve, espe-
cially when ring clips are used for
mounting. The insulation can be im-
proved by using an insulating strip.
In such cases, attention must be
paid to any relevant regulations
(e.g. VDE, BSA or UL regulations).
Upper category tempera-
ture (UCT)
The upper category temperature is
the maximum permissible ambient
temperature at which a capacitor
may be continuously operated. If
this limit is exceeded, the capacitor
may fail prematurely.
For some type series, however, op-
eration at temperatures above the
UCT is permissible for short periods
of time. The maximum permissible
operating temperatures are specified
in the data sheets for the individual
type series under "Specifications
and characteristics in brief", section
"Useful life".
Maintenance
Make periodic inspections for the
capacitors that have been used in
the devices for industrial applica-
tions. Before the inspection, make
that the power supply is turned off
and carefully discharge the electricity
of the capacitors. To check the
capacitors, make sure of the polarity
when measuring the capacitors by
using a volt-ohm meter, for instance.
Also, do not apply any mechanical
stress to the capacitor terminals.
The following items should be
checked by the periodic inspections.
Significant damage to appearances:
venting, electrolyte leakage, etc.
Electrical characteristics: leakage
current, capacitance, tan
and other
characteristics prescribed in the
catalogs or product specifications.
If any of the above is found, replace
it or take any other proper measure.
Halogenated hydrocarbons may
cause serious damage if allowed to
come into contact with aluminum
electrolytic capacitors.
Mounting position
An overpressure vent ensures that
the gas can escape when the pres-
sure reaches a certain level.
To prevent electrolyte from leaking
out when the gas is “vented”, the
capacitor should be mounted in an
upright position (90°). All of these
mounting positions are intended to
avoid a vent-down installation of the
capacitor.
Mounting of single-ended
capacitors
For further information see page 67.
Soldering
Excessive time or temperature dur-
ing soldering will affect capacitor’s
characteristics and cause damage
to the insulation sleeve. Capacitors
should be dipped in solder for less
than 10 seconds. Contact of the
sleeve with soldering iron must be
avoided.
Soldering, cleaning agents
Halogenated hydrocarbons may
cause serious damage if allowed to
come into contact with aluminum
electrolytic capacitors. These sol-
vents may dissolve or decompose
the insulating film and reduce the in-
sulating properties to below the per-
missible level. The capacitor seals
may be affected and swell, and the
solvents may even penetrate them.
This will lead to premature compo-
nent failure.
Because of this, measures must be
taken to prevent electrolytic capaci-
tors from coming into contact with
the solvents when using halogenat-
ed hydrocarbon solvents to clean
printed circuit boards after soldering
the components, or to remove flux
residues. If it is not possible to pre-
vent the electrolytic capacitors from
being wetted by the solvent, halo-
gen-free solvents must be used in
order to eliminate the possibility of
damage.
Passive flammability
Under the influence of high external
energy, such as fire or electricity, the
flammable parts may get inflamed.
Clause 38 of the relevant specifica-
tion CECC 30000 (Harmonized
System of Quality Assessment for
Electronic Components; Generic
Specification: Fixed Capacitors)
refers to IEC Publication 695-2-2
(Needle Flame Test) for testing the
passive flammability of capacitors.
And in CECC 30000, severities and
requirements for different categories
of flammability are listed. Most of
aluminum electrolytic capacitors
meet the requirements of category C.
Active flammability
In rare cases the component may
ignite caused by heavy overload or
some capacitor defect. One reason
could be the following: During the
operation of an aluminum electrolytic
capacitor with nonsolid electrolyte,
there is a small quantity of hydrogen
developed in the component. Under
normal conditions, this gas perme-
ates easily out of the capacitor. But
under exceptional circumstances,
higher gas amounts may develop
and may catch fire if a sparking
would occur at the same time.
As explained above a fire risk can’t
be totally excluded. Therefore, it is
recommended to use special mea-
sures in critical applications (e.g. ad-
ditional encapsulation of the equip-
ment for mining applications).
