UPS topology affects how equipment receives power and how the UPS responds to changes in the incoming supply.
Practical example: protecting a small server rack
Capacity and runtime are separate UPS sizing questions.
Scenario: A rack contains a server, NAS, managed switch and router. Their illustrative planning load totals 860 W.
Adding 25 percent design headroom gives approximately 1,075 W. The UPS must support both the required watt load and VA load. Runtime is then checked separately against the manufacturer's runtime data for the exact UPS and battery configuration.
Decision: First confirm capacity, then decide whether the objective is only to bridge short interruptions, allow an orderly shutdown or maintain operation for a longer period. Each objective produces a different battery requirement.
Common mistakes and selection checklist
Common mistakes
- Selecting a UPS from VA alone without checking its watt rating.
- Assuming the advertised maximum runtime applies to the actual rack load.
- Connecting equipment without considering startup load, growth or the UPS topology required by the application.
What happens if you get it wrong?
The UPS may overload, provide far less runtime than expected, or fail to achieve the intended objective of bridging an outage or allowing an orderly shutdown.
Selection checklist
- Measure or estimate the real watt load of the equipment being protected.
- Check both the UPS watt and VA capacity.
- Add sensible design headroom for growth and transient load.
- Use the manufacturer's runtime data for the exact model and load.
- Define whether the goal is ride-through, graceful shutdown or extended operation.
Line-interactive UPS
Line-interactive UPS systems can regulate incoming voltage while providing battery backup when required. They are commonly used for business equipment and network devices where this level of protection is appropriate.
Online double-conversion UPS
Online UPS systems use a double-conversion architecture in which the load is supplied through the UPS conversion system. This provides a different level of power conditioning and isolation from incoming supply variations.
Which should you choose?
The decision should consider the sensitivity of the equipment, the quality of the incoming power, the consequences of interruption and the budget available for the power protection system.
| Consideration | Line-interactive | Online |
|---|---|---|
| Power protection approach | Regulation and battery backup | Double-conversion architecture |
| Typical application | Business and network equipment | More demanding infrastructure applications |
| Equipment requirements | Depends on installation | Suitable where continuous conditioned power is required |
| Cost and complexity | Generally lower | Generally higher |
The exact capabilities vary between UPS models, so the manufacturer's specifications should be checked before selection.
Confirm the exact product specification, supported configuration and compatibility before ordering. Platform generation, firmware, licences and optional components can change what a product supports.