A screw-terminal aluminum electrolytic capacitor may look like a simple voltage-and-capacitance purchase. In a VFD DC bus, however, the wrong ripple rating, cooling assumption, or terminal layout can force a costly second sample. These five checks make the first RFQ more useful.
1. Start with the highest DC-bus voltage
Send the normal bus voltage and the highest value expected during line variation, regeneration, or braking. Do not select from the nominal motor voltage alone. If capacitors will be connected in series, describe the balancing method and the expected voltage distribution across each unit.
2. Match ripple current at the real frequency
Ripple current produces internal heat through ESR, and both ESR and allowable ripple current vary with frequency. That is why an RFQ should include RMS ripple current, the main frequency components, ambient temperature, airflow, and duty cycle. A catalogue current value without its test conditions is not enough for a reliable comparison.
3. Treat cooling as part of the component choice
Manufacturer guidance shows that temperature rise from ripple current strongly affects expected life. Record the capacitor position, nearby heat sources, ventilation, and whether the can base is cooled. Ask for a life estimate based on the selected series and your actual operating conditions rather than a generic rule of thumb.
4. Confirm mechanical details before the sample
Provide the maximum diameter and height, clamp style, terminal spacing, busbar orientation, polarity marking needs, and required vent clearance. During assembly, follow the specified terminal torque; the electrical match does not correct a stressed terminal or blocked safety vent.
5. Send a complete RFQ
A practical request includes capacitance and tolerance, working and peak voltage, ripple current with frequency, ambient and cooling, target service life, dimensions, terminals, application, annual quantity, and sample quantity. Photos or a drawing of the existing installation are especially helpful for replacement projects.
Validate the sample in the real cabinet
Before production approval, measure the bus waveform and capacitor case temperature under the worst repeatable load. Recheck polarity, terminal torque, clamp security, and vent clearance after the thermal run. This short validation catches assumptions that a datasheet review cannot.
Can two parts with the same voltage and capacitance be interchangeable? Not automatically. Ripple rating, ESR, lifetime conditions, dimensions, and terminals can differ.
What should buyers send first? A bus-voltage range, ripple data, thermal conditions, envelope drawing, and required quantity are the fastest starting point.
Need a screw-terminal capacitor match for a VFD, UPS, or industrial power supply? Send LORIDA your operating data and mechanical drawing. We can review the RFQ and prepare a sample proposal for verification.
Technical basis: aluminum-electrolytic capacitor application guidance from TDK Electronics and Nippon Chemi-Con. Final selection should follow the datasheet and specification for the exact series supplied.
