Solid State Relay Application Guide
š” FAE Insights
Technical Logic
1) Determine load type (AC or DC); 2) Select current rating with adequate derating; 3) Design heat sinking for thermal management; 4) Implement protection circuits for inductive loads.
š Customer Cases
Industrial Oven Manufacturer
Challenge
Mechanical relays failing every 3-6 months in temperature control
Solution
Replaced with KSR-TRIAC-10A SSRs with proper heat sinking
Customer Feedback
"5-year maintenance-free operation with improved temperature accuracy"
Results
Successful implementation with reliable performance
Frequently Asked Questions
1. When should I use an SSR instead of a mechanical relay?
Use SSRs for: high switching frequency (>1/minute), silent operation requirements, fast switching needs (<1ms), explosive/dusty environments, vibration-prone applications, precise control/PWM. Use mechanical relays for: very low on-resistance (<10mĪ©), complete galvanic isolation, very high current (>100A), cost-sensitive low-frequency switching.
2. Why is my SSR overheating?
SSR overheating is typically caused by: insufficient heat sinking, excessive load current, high ambient temperature, or inadequate derating. Solutions: verify heat sink thermal resistance is adequate, reduce load current or upgrade SSR rating, improve ventilation, check for loose connections causing additional heating. Always measure case temperature - should not exceed 85Ā°C under normal operation.
3. Can SSRs be used for motor speed control?
Standard on/off SSRs cannot be used for motor speed control. For AC motor speed control, use phase-control SSRs (random switching type) with appropriate control circuit. For DC motors, use PWM-controlled DC SSRs or motor driver ICs. Motor applications require careful consideration of inrush current (5-7Ć running current) and proper protection circuits. Contact BeiLuo FAE for motor control guidance.
4. What causes SSR failure?
Common SSR failure causes: overcurrent beyond rating, overvoltage transients (especially with inductive loads), overheating from inadequate heat sinking, excessive inrush current, and short-circuit conditions. Prevent failures by: proper current derating, protection circuits for inductive loads, adequate heat sinking, fast-acting fuses for short-circuit protection. Cosmo SSRs include internal protection but external protection is recommended.
5. Can SSRs be connected in parallel for higher current?
Paralleling SSRs is possible but challenging due to current imbalance. If paralleling is necessary: use SSRs from same batch with matched characteristics, implement current balancing resistors, monitor temperatures to detect imbalance, ensure adequate heat sinking for combined dissipation. Often better to use single higher-rated SSR or contactors for very high current. Cosmo offers SSRs up to 10A; contact us for higher current solutions.