ftcap - Industrial Electronics GmbH

3. Parameter
3.1 Rated voltage
C
C 20°C
1,1
1
0,9
FTCAP
Capacitance
as a function of ambient temperature T
0,8
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
T [°C]
Aluminium Electrolytic Capacitors
The rated voltage (UR) is the voltage the capacitor is designed for. This voltage may be applied continously to the
capacitor over the full temperature range.
3.2 Surge voltage
The Surge voltage may be applied to the capacitors only for a short time.
UR � 315 V : US =1,15 * UR ( 5 times 1 min per hour)
UR > 315 V : US =1,1 * UR ( 5 times 1 min per hour)
3.3 Ripple voltage
In many applications the voltage applied to capacitors is a combination of direct and alternating voltage. Pay attention to
the following points:
� The superposition of AC and DC must not exceed the rated voltage.
� Reverse voltage is not allowed.
� The applied ripple current must not exceed the rated ripple current.
3.4 Maximum reverse voltage
The Aluminium Electrolytic Capacitor is a polar component. Diodes with a max. conducting state voltage of 0.8 V could be
used to prevent reverse polarity voltage. Single shorttime reverse polarity of V < 1.5 V for t < 1 s is tolerated.
3.5 Rated capacitance
The rated capacitance is usually determined at 100 Hz and 20 °C . In general the rated capacitance is marked on the
capacitor in µF.
3.6 DC and AC capacitance
The capacitance determined by AC measurements is smaller than the capacitance determined by charge / discharge
measurements.
In most applications the capacitor is applied to an alternating voltage so in general the capacitance is measured with the
AC method.
3.7 Capacitance vs temperature and frequency
The capacitance varies with temperature and frequency
� The capacitance increase with increasing temperature
� The capacitance decrease with increasing frequency
The following diagrams exhibit typical courses of these dependences
5
1,2
1,1
1
0,9
Capacitance C / C 100Hz
- typical -
as a function of the frequency f
0,8
10 100 1000 10000 100000
Frequency [Hz]
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