Grid Resilience in the Home Office

Mumbai's grid is a probabilistic system. You don't ask if the power will drop. You ask when, for how long, and what's your P99 recovery.

After 18 months of logging: median outage duration is 4.3 minutes. P90 is 12 minutes. P99 is 47 minutes (that was the night a feeder transformer exploded in Mahalaxmi).

Setup:

• APC Smart-UPS 1500VA: powers the desk stack (laptop dock, two monitors, network gear, one office light). Runtime at typical load: 32 minutes.
• Honda EU20i generator in the storage room for >30 min outages. Auto-start via a relay triggered by UPS on-battery signal. Fuel: 5L tank, runs ~4 hours.
• Starlink as secondary WAN (primary: JioFiber). Auto-failover via a MikroTik router with recursive routing. Cutover time: ~8 seconds.
• Everything on a sub-panel with a manual transfer switch. No backfeeding, no electrocution hazard.

The generator auto-start was the hardest piece. The UPS serial port signals 'on battery' via a dry-contact pin. A Wemos D1 reads that pin, fires a 12V relay that cranks the generator starter solenoid. Then a separate vibration sensor on the generator frame confirms it fired. If no confirm within 5 seconds, it re-cranks.

Three components fail most often: the generator battery (replace yearly), the relay module (corroded contacts in the humidity), and my patience. The rest is engineered.