947C Datasheet, PDF (6/8 Pages) Cornell Dubilier Electronics – Polypropylene, DC Link Capacitors

Type 947C Polypropylene, DC Link Capacitors
High Current, High Capacitance for Inverter Applications
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=mW
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. The dielectric resistance
needs to be considered for operation below 10kHz.
1. Start with the 10kHz ESR from the ratings table. If frequency is
less than 10kHz, use the following equation: ESR - 31.83/(10C) +
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. 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)].
Please note that the θcc for all designs built to figures 1 and 2; 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.
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
The expected lifetime predictions assume no exposure to overvoltage transients.
Expected lifetime can be calculated for varying exposure to overvoltage transients.
As an illustration at 50 °C the expected lifetime is 100,000 h with the 24-hour Va ∕ Vr
profile below:
Va / Vr
1.67
1.50
1.30
1.10
1.00
Duration
100 ms
5 minutes
2.5 hours
9.6 hours
11.9 hours
For applications with more severe 24-hour profiles, contact us.
CDE Cornell Dubilier • 1605 E. Rodney French Blvd. • New Bedford, MA 02744 • Phone: [phone] • Fax: [phone]
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