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ITGlossary · Power quality
AC Ripple
A small unwanted AC component on the DC charging voltage of a UPS that heats the batteries and shortens their life.
Technical level:Advanced
AC ripple appears when rectification and filtering in the charger or on the DC bus of a UPS are not perfect. Instead of a clean direct voltage, the battery also receives a small alternating component that makes it charge and discharge very slightly, many times per second.
The result is extra heat and faster ageing, especially in sealed lead-acid (VRLA) batteries. For this reason battery manufacturers specify a maximum permissible ripple current, and good UPS units include suitable filtering.
If batteries run hot, swell or lose capacity much earlier than expected while the room temperature is normal, ask a technician to measure the ripple at the charger before simply replacing the batteries.
Related terms
- DC VoltageRefers to the direct current (DC) voltage level, typically that of a UPS battery.
- AC ChargingCharging with alternating current, where the vehicle's on-board charger converts it to direct current to fill the battery.
- DC ChargingFast charging in which the station converts power to direct current and feeds it straight into the battery, typically at 50 to 350 kW.
- Automatic Voltage Regulator (AVR)A device that automatically maintains a constant voltage level to protect electrical equipment from fluctuations.
- Electromagnetic Interference (EMI)Unwanted electrical noise or interference that can disrupt electronic equipment operation.
- Equalising ChargeA controlled charge at a higher than normal voltage that brings all cells of a lead-acid battery to the same state of charge.