Overview
A motor drive or inverter converts a DC bus into a variable-frequency waveform, and the capacitor bank across the DC link is one of its most stressed components. The link capacitor carries the switching ripple, supplies the pulses the inverter draws during a commutation and smooths the voltage the switches see. In a high-duty drive it is often the capacitor that sets the service life of the whole product, so it deserves a careful choice. CapXon supplies the aluminum electrolytic capacitors, and BeiLuo backs them with genuine traceability and engineering support.
The DC-Link Capacitor Bank
The DC link of a drive carries a large ripple current at the switching frequency, so the bank must be rated for that ripple across the expected case temperature. The voltage rating must exceed the peak bus with margin for the regeneration overshoot, which is why a 400 V or 450 V class is common even when the nominal bus is lower. A snap-in capacitor such as the CapXon UJ series offers a high capacitance and a long life in a compact can that mounts directly on the board without a clamp, and the standardized terminal spacing keeps the bank layout uniform.
Why a Bank
Several capacitors in parallel share the ripple current, reduce the equivalent ESR and ESL and fit a flatter mechanical envelope than a single very large can. They also reduce the stored energy per can, which is easier for safety and easier to source. Keep the busbar impedance balanced so the current shares evenly, and verify the ripple on each capacitor under load rather than assuming an even split.
Ripple and ESR
The ripple current rating depends on the frequency and the case temperature, so use the datasheet multiplier at the switching frequency and derate for the ambient. A low-ESR capacitor carries more ripple than a calculation based on capacitance alone suggests, so measure the actual ripple on the bench and compare it with the derating curve.
Auxiliary and Control Rails
Beyond the DC link, a drive has gate-drive, control and communication rails that need their own capacitors. These are usually lower-voltage and lower-power, so a compact radial capacitor such as the CapXon KM or LE series fits the dense control board. Where the auxiliary rail sits across a high-voltage barrier, a high-voltage radial part such as the LE or KY series is used, and its long life suits equipment that runs continuously.
Isolation and Layout
An auxiliary capacitor across an isolation barrier must respect the creepage and clearance for the voltage, and its layout must keep the high-voltage side separated from the low-voltage logic. Keep the loop small and the capacitor close to the load it supplies, so the noise decoupling is effective.
Thermal Design and Lifetime
The life of the DC-link capacitor depends on its core temperature, which is the ambient plus the ripple heating, so the thermal design is part of the electrical design. Space the capacitors for airflow, keep them away from the switching devices and the braking resistor, and choose a long-life series where the drive runs continuously. A 12000-hour series such as the CapXon LE range or a 5000-hour snap-in such as the UJ range gives a much longer service interval than a general-purpose part.
Measure and Verify
Measure the case temperature at worst-case load and ambient, compare it with the derating curve and confirm the ripple margin, then estimate the lifetime from the endurance and the temperature rule. This evidence turns a capacitor choice into a verified design decision.
Getting Help
Send your bus voltage, ripple, switching frequency, duty cycle and life target to our FAE team and we will propose a capacitor bank with the capacitance, voltage, case and lifetime, then quote from stock. BeiLuo holds mainstream CapXon snap-in and radial models in regional warehouses and ships every order with an import declaration, a certificate of origin and a RoHS compliance file, so a drive design can move from prototype to production without a supply gap. Engineer-level support covers the whole selection, from the bank calculation through validation and volume supply.