Battery Backup Time
Q: What does battery backup mean? How much do I need?
A: Battery autonomy / backup is the time the load continues to run when the Eskom supply fails. Longer runtime means a larger battery bank and higher purchase cost.
Two patterns:
- Generator-bridged: UPS only carries the load for the few minutes the generator takes to start. This is the recommended pattern for sites that experience frequent (daily / weekly) outages — long-runtime UPS batteries used for daily load shedding age fast and cost more long-term than a small UPS plus a generator.
- Long-runtime UPS: sized for the full outage duration (hours). Expensive on three fronts: capital cost (large battery bank), space, and total cost of ownership (a normal UPS battery handles only 200–300 full discharges, so cyclic use accelerates replacement).
Battery discharge is non-linear with load — a 5-minute design at 100% load will give well over 10 minutes at 50% load. So shedding non-critical loads (FAQ - Load Shedding Strategy) extends backup time meaningfully.
Connections
- Eskom — referenced, source: https://standbysystems.co.za/ups-batteries-questions-and-answers/
- FAQ - Load Shedding Strategy — relates, source: https://standbysystems.co.za/ups-batteries-questions-and-answers/