How does an inverter or UPS work?

When the power cuts out and the fans keep turning, a box in the corner is quietly turning a battery's DC back into 230 V AC. A home inverter is a battery, a charger and an inverter in one box.

Read how it works: How does an inverter or UPS work? · The history of the inverter and the UPS · More boxes on Glassbox

Chapters in this interactive model

1. Inside a home inverter and a UPS: A battery, a charger and an inverter: store electricity now, give it back in a power cut.
2. Turning AC into DC: Four diodes flip the backwards half of every wave, and a capacitor smooths the bumps.
3. Turning DC back into AC: Four switches flip the battery back and forth, and a transformer lifts 12 V to 230 V.
4. Power cut! Switching in milliseconds: How fast the backup takes over decides whether your computer notices.
5. How long will the backup last?: Battery energy divided by what you switch on, with a few real-world catches.
6. Inside the battery: Lead, lead dioxide and acid: a chemical reaction you can run forwards and backwards.