947C361K801CAMS Datasheet, PDF (3/4 Pages) Cornell Dubilier Electronics – Type 947C High Capacitance, High Current, DC Link Capacitors

Type 947C High Capacitance, High Current, DC Link Capacitors
Expected Lifetime Predictions
To use the Expected Lifetime curves calculate Va ⁄Vr and core
temperature T. Start by estimating:
Applied dc voltage Va
Ripple Current I
Ripple Frequency f
Ambient Temperature Ta
Airflow speed v
Units:
A=m²
T, Ta & Tc=°C
C=µF
θ, θca & θcc =°C/W
ESR=mΩ
v=m/s
f=kHz
Va &Vr=Vdc
I=A
NOTE: The temperature rise in the 947C is I²(ESR) times the
thermal resistance θ. The ESR is mainly the metal resistance;
the metal resistance is the 10 kHz ESR. For operation below 10
kHz add the dielectric resistance. It is the dielectric dissipation
factor—no more than 0.0002—times the capacitive reactance,
i.e., 0.0002 ⁄(2πfC). That’s equal to 31.83 ⁄(fC).
1. Start with the 10 kHz ESR from the Ratings table. If frequency is
less than 10 kHz, add 31.83 ⁄(fC).
2. Compute total thermal resistance θ as the sum of core-to-case
thermal resistance θcc and case-to-ambient thermal resistance
θca. Both are in the Ratings table but θca is for still air and θcc
is for 10 kHz or less. For frequency > 10 kHz multiply θcc by
[1+(f –10)/100], e.g., for 75 kHz multiply θcc by 1.65. For moving
air use the capacitor surface area A and airflow speed v to calculate
θca = 1 ⁄[A(5+17(v+0.1)^0.66)].
3. Compute Va ⁄Vr and the core temperature T.
T = Ta + I²(ESR)θ
4. Look up estimated lifetime from the Expected Lifetime curves.
5. If you want a longer expected lifetime, choose a capacitor with
higher voltage rating or consider using multiple capacitors in parallel
to share the ripple current.
Permissible Voltage Surge Duty for 100,000 Hour
Life Expectancy at 50 ºC Core Temperature
Factor
1.67x
1.50x
1.30x
1.10x
1.00x
Duration
Frequency
t≤ 100 ms
1x/day
t≤ 5 minutes
1x/day
t≤ 2.5 hours
1x/day
t≤ 9.6 hours
1x/day
balance (11.9 h) 1x/day
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