Oct 6, 2026Capacitor Selection
UPS Capacitor Bank Replacement: One Capacitor or the Whole Bank?
One failed capacitor in a UPS DC-link bank? Learn when a single replacement may be reasonable, when to review the whole bank, and what to check before restarting.
A customer finds one failed aluminum electrolytic capacitor in a UPS DC-link bank. The immediate question is understandable: Can we replace this one part and get the UPS running again?
Sometimes a single replacement is possible. But the failed capacitor does not tell you enough about the condition of the others.
Capacitors in the same bank may have operated for years under similar loads and conditions. If one has reached the end of its service life, others may be close behind. On the other hand, a damaged terminal, an open branch fuse or another local fault may explain why only one unit failed.
Check the bank before deciding
After the UPS has been safely isolated and discharged by qualified personnel, review each capacitor individually. Compare its condition and measurements with the correct specifications, and check the connections, fuses and busbar. Record the age of the bank and any earlier replacements.
Then look for the cause of the failure. If the bank is aging as a group, replacing only the visibly failed unit may mean another shutdown soon. A planned bank replacement can make more sense for equipment where an unexpected outage is costly.
If testing points to an isolated fault and the remaining capacitors meet the equipment requirements, a partial replacement may be an option. Follow the UPS manufacturer's service instructions and verify that the new capacitor is suitable for the bank. Matching voltage and capacitance on the label alone is not enough.
The practical answer
Do not decide from the failed capacitor alone. Check the whole bank, find out why that unit failed, and weigh the replacement cost against the cost of another outage.
If you are reviewing a UPS capacitor bank, send COREVIA the capacitor specification, quantity, bank age, equipment model and fault history. We can help you review the replacement requirements.
