Aishi Capacitor Selection Guide
Introduction
aishi aluminum electrolytic capacitors are essential components in power supply circuits. This guide helps engineers select the right capacitor for their applications.
Key Selection Parameters
1. Capacitance Value
- Determine required capacitance based on ripple voltage requirements
- Consider tolerance (typically +/-20% for electrolytic capacitors)
- Account for capacitance decrease over lifetime
2. Voltage Rating
- Select rated voltage at least 1.25x the maximum working voltage
- Higher voltage ratings improve reliability and lifetime
- Consider surge voltage capability for transient conditions
3. Ripple Current
- Calculate expected ripple current from switching frequency and load
- Select capacitors with rated ripple current >= 1.5x calculated value
4. Temperature Rating
- Standard: 85C (2000 hours rated life)
- High temperature: 105C (2000-10000 hours)
Recommended Aishi Series
- RS Series: General purpose radial capacitors
- RH Series: High temperature radial capacitors
- Snap-in Series: High capacitance for power supplies
- Screw Terminal: High power industrial applications
💡 FAE Insights
📋 Customer Cases
Challenge
Customer experienced capacitor failures in industrial power supplies
Solution
Recommended upgrading to 105C rated capacitors with 80% voltage derating
Customer Feedback
"Customer reported excellent results with improved reliability."
Frequently Asked Questions
1. What is the recommended voltage derating for Aishi capacitors?
Industry best practice recommends operating aluminum electrolytic capacitors at no more than 80% of their rated voltage. This means operating a 400V capacitor at maximum 320V. The 20% margin provides protection against voltage transients, line surges, and ensures long-term reliability. For critical applications or high-reliability designs, 50% derating may be used. Higher derating significantly extends capacitor lifetime - operating at 50% voltage can provide 4-8x longer life than operating at 100% voltage.
2. How does temperature affect capacitor lifetime?
Temperature has an exponential effect on capacitor lifetime following the Arrhenius equation. For every 10°C decrease in operating temperature, lifetime approximately doubles. Conversely, every 10°C increase halves the lifetime. This relationship is fundamental to capacitor reliability engineering. For example, a capacitor rated for 5,000 hours at 105°C will last approximately 20,000 hours at 85°C, 80,000 hours at 65°C, and 320,000 hours at 45°C. Proper thermal management is therefore critical for achieving long capacitor lifetime.
3. How do I select the right capacitance value for my application?
Capacitance selection depends on the application requirements. For input filtering, calculate based on hold-up time requirements: C = (P × t) / (0.5 × V²), where P is power, t is hold-up time, and V is voltage drop. For output filtering, calculate based on allowable ripple voltage: C = I_ripple / (f_sw × ΔV_ripple), where I_ripple is ripple current, f_sw is switching frequency, and ΔV_ripple is allowable voltage ripple. For energy storage, calculate based on energy requirements: C = 2 × E / V², where E is energy and V is voltage. Always add 20-30% margin to calculated values.
4. What is ripple current and why is it important?
Ripple current is the AC current component flowing through a capacitor, typically at the switching frequency in power supplies. It causes internal heating due to the capacitor's ESR (Equivalent Series Resistance), which degrades the capacitor over time. Excessive ripple current leads to accelerated aging, reduced lifetime, and potential failure. Each capacitor has a maximum rated ripple current that must not be exceeded. When selecting capacitors, calculate the expected ripple current in your application and choose a capacitor with adequate ripple current rating, typically with 20-30% margin.
5. When should I use 105°C rated capacitors instead of 85°C?
Use 105°C rated capacitors when: (1) The ambient temperature exceeds 60°C, (2) The capacitor will be in an enclosed space with limited airflow, (3) Long lifetime is required (>10,000 hours), (4) The application is safety-critical or difficult to service, (5) High ripple current causes significant self-heating. The 105°C rating provides 2-4x longer lifetime at the same operating temperature compared to 85°C capacitors. While 105°C capacitors cost 20-30% more, the improved reliability and extended lifetime often justify the cost in demanding applications.