Overview
Inverters and motor drives are among the highest-volume applications for large aluminum electrolytic capacitors, because the DC link that feeds the switching bridge must both store energy and smooth the ripple that the bridge draws. The capacitor bank sets the bus ripple, the hold-up time and, to a large extent, the reliability of the drive. AiSHi screw-terminal and snap-in capacitors serve this role, and BeiLuo supplies them with genuine traceability and FAE support.
The DC Link and Its Ripple
A motor drive converts a DC bus into three-phase AC, and the switching bridge draws a pulsed current from the bus. The DC-link capacitor supplies that pulse, so it sees a large ripple current at the switching frequency in addition to the DC voltage. A screw or lug terminal capacitor is used here because its busbar connection handles the high current and its large can dissipates the ripple heating; the AiSHi LM series offers a 105 °C grade with a 3000-hour endurance and a high ripple rating. The 250 V and 315 V classes cover the common drive bus voltages with margin for switching overshoot.
Sizing the Bank
The capacitance sets the bus ripple and the hold-up time, and the total ripple rating sets how much pulse current the bank can absorb. Because the capacitance is large, several capacitors are often paralleled on a busbar; each carries a share of the ripple, so the bank ripple rating is the sum of the individual ratings. Keep the busbar impedance balanced so the current shares evenly, and verify the ripple on each capacitor under load.
Life and Thermal Design
An aluminum electrolytic capacitor ages with its core temperature, and the core temperature is set by the ambient, the case thermal resistance and the ripple heating. Lifetime roughly doubles for every 10 °C reduction in core temperature, so keeping the capacitors cool is the most effective way to make the drive last. Space the cans for airflow, keep them away from the hottest components, and check the ripple margin at the worst-case case temperature. The long-life AiSHi series extend the life further when servicing is difficult.
Auxiliary and Control Rails
Alongside the DC link, a drive has auxiliary and control rails that need their own bulk capacitance. Here the current is lower and the voltage may also be lower, so a snap-in capacitor that mounts directly on the PCB is convenient and space-efficient. An AiSHi LM series snap-in part provides the hold-up and filtering for a low-voltage rail, while a higher-voltage snap-in part suits a higher rail.
Selection and Supply
Selection starts with the bus voltage and the required capacitance and ripple, then narrows by case size, terminal type and lifetime, choosing a screw or lug terminal part for the high-current DC link and a snap-in part for the lower-current rails. BeiLuo keeps mainstream AiSHi capacitors in regional stock, ships them with import declaration, certificate of origin and RoHS documents, and supports ripple, lifetime and layout design with an in-house FAE team. From a compact servo drive to a large industrial inverter, our engineers help you choose the capacitors that keep the drive reliable and the bus stable.