405DLR2R5K Datasheet, PDF (3/4 Pages) Illinois Capacitor, Inc. – Super capacitor

DLR
Supercapacitor
Application Guidelines
1. Do not apply a reversed voltage.
Reverse polarity is not recommended. If a reversed
voltage is applied for a long time, the leakage current will
increase abruptly, which may cause a decrease in the
capacity, an increase in the internal resistance, and cause
electrolyte leakage or damage to the capacitor in some
cases.
2. Do not apply any voltage higher than the operating
maximum voltage.
Supercapacitors are rated with a nominal recommended
working or applied voltage. If an over voltage is applied to
the capacitor, the leakage current will increase abruptly
and the capacitor will become overheated, which may
cause a decrease in the capacity, an increase in the
internal resistance, and cause leakage or damage to the
capacitor in some cases. But, surge voltage can usually
be tolerated by the super capacitor.
3. Ripple Current
Supercapacitors have a higher internal resistance than
aluminum electrolytic capacitors and are more
susceptible to internal heat generation when exposed to
ripple current, this may cause a decrease in the capacity,
an increase in the internal resistance, and cause electrolyte
leakage or damage to the capacitor in some cases.
4. Charging and Discharging.
Supercapacitors can be charged using various methods,
including constant current, constant power, constant
voltage or by paralleling to an energy source, i.e. battery,
fuel cell, DC converter, etc. In general, characteristics of
constant current and constant resistance discharging are
respectively represented by the equation (1) and (2) below:
Discharging time (t) of constant current discharge
t = C x (Vo-V1) / l…..(1)
Discharging time (t) of constant resistance discharge
t = -CRIn(V1/Vo)…..(2)
t = discharging time(s)
vo = initial voltage (v)
v1 = terminal voltage (v)
l = current during back-up (A)
The maximum recommended charge current, I, for a super
capacitor is calculated as follows:
I = Vw / 5R
where Vw is the charge voltage and R is the super
capacitors DC ESR
5. Do not use in a circuit where quick charge and
discharge are repeated very often.
In a circuit where quick charge and discharge are
repeated very often, the capacitor will become
overheated, which may cause a decrease in the
capacitance, an increase in the internal resistance, and
cause electrolyte leakage or damage to the capacitor in
some cases. Reduce the charge and discharge currents
while selecting a capacitor with low internal resistance,
and make sure that the capacitor surface temperature
does not rise more than 10˚C.
6. Super capacitor life depends on the ambient
temperature.
The lifetime of super capacitor is seriously affected by
change in ambient temperature. If the temperature is
lowered by 10˚C, the lifetime will be approximately
doubled. As a result, it is recommended to use the super
capacitor at the lowest temperature possible to decrease
internal degradation and ESR increase. If the capacitor is
used at a temperature exceeding its maximum guaranteed
temperature, not only is its life shortened, but increased
vapor pressure of electrolyte or electrochemical reactions
may increase the internal pressure, and cause electrolyte
leakage or damage to the capacitor in some cases.
7. Voltage drop occurs during back-up operation.
In applications where the discharge current is large, or a
large current flows instantaneously, super capacitor may
not operate at the start of discharge because of the large
voltage drop (IR drop) caused by the capacitors internal
resistance (ESR). The formula for the voltage drop, Vdrop,
during a discharge at I current for t seconds is:
Vdrop = I(R + t/C)
8. Series Connecting of super capacitor.
A series connection can cause an imbalance in the
voltage across a super capacitor causing the capacitors
to have an over voltage which can cause electrolyte
degradation, excessive gas generation, increased ESR,
decrease in capacitance and reduced life. To prevent
voltage imbalance, passive or active voltage balancing is
recommended. Passive voltage balancing should be
performed using divider resistors placed in parallel with
the super capacitors. Using resistance values between100
Ω/F to 470 Ω/F are recommended.
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