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2026-09-22
ACwatt| Mode | Power path | Purpose | Limitation |
|---|---|---|---|
| Normal | Rectifier → inverter → load | Continuous protection | Normal operation required |
| Battery | Battery → inverter → load | Input failure | Limited runtime |
| Bypass | Bypass source → load | Overload, fault or maintenance | Reduced inverter conditioning |
| ECO | Bypass source → load | Higher efficiency | Different protection level |
| Self-aging | Internal test circulation | Burn-in testing | Follow approved procedure |
Why UPS operating modes matter
A UPS does more than switch from utility power to batteries. Its operating mode determines how power flows through the rectifier, inverter, bypass path and battery system. Understanding these modes helps operators interpret the display, review alarms and select a safe state for maintenance or testing.
Normal mode
In normal mode, the rectifier receives utility power, the inverter supplies the load and the charger maintains the battery. ACwatt ACS documentation shows the REC, INV and BYP status indicators on the interface. This is the default operating state for continuous protection in ACS Series online UPS systems.
Battery mode
When the input supply fails or moves outside the permitted range, the battery supplies the inverter. The inverter continues feeding the load until utility power returns or the battery reaches its shutdown threshold. Runtime depends on load, battery capacity, voltage, efficiency and temperature. For battery-backed protection in server rooms, see our UPS systems.
Bypass mode
In bypass mode, the load receives power directly from the bypass input rather than the inverter. This may occur during overload or fault conditions and may be selected during maintenance. The ACS documentation notes that direct bypass does not provide the same surge protection as inverter operation. For three-phase UPS systems, bypass mode is often used during scheduled maintenance.
ECO mode
ECO mode feeds the load through the bypass path while the inverter remains on standby. The supplied ACS documentation states that ECO mode can reach up to 98% efficiency, but power conditioning differs from online mode. The choice depends on load sensitivity and site power quality. In modular UPS deployments, ECO mode is often used when the load is not sensitive and the site power quality is stable.
Self-aging mode
Self-aging mode allows an operator to burn in the UPS without connecting a full external load bank. The ACS documentation describes an internal circulation path with approximately 5% loss while testing at full load. Use this mode only according to the approved manual and commissioning procedure. ACwatt's manufacturing and testing process uses this mode during factory burn-in for ACM Series modular UPS.
Parallel and frequency-converter modes
Parallel mode connects UPS units for larger capacity or a defined redundancy design. The exact configuration depends on the model and approved kit. ACS 6–20kVA documentation also identifies frequency-converter mode. In that mode, input and output frequencies differ, bypass is unavailable and the load must be derated according to the product instructions.
When to use which mode
| Scenario | Recommended mode | Reason |
|---|---|---|
| Daily operation | Normal | Full-time protection |
| Utility outage | Battery | Seamless transfer |
| Overload or fault | Bypass | Protect the inverter |
| Non-sensitive load, efficiency priority | ECO | Up to 98% efficiency |
| Factory burn-in | Self-aging | Internal test without external load bank |
Operator checks
- Confirm the mode shown on the LCD before switching bypass.
- Record alarms and event history before changing the operating state.
- Identify whether battery mode is caused by an outage or input-range issue.
- Do not present ECO efficiency as the same protection level as online double conversion.
- Use self-aging mode only with safety controls and the approved procedure.
Frequently Asked Questions
Does bypass mode protect the load from surges?
The supplied ACS documentation states that direct bypass cannot provide the same surge protection as inverter operation.
What is the difference between battery mode and ECO mode?
Battery mode uses the battery and inverter. ECO mode normally uses the bypass path to improve efficiency.
Can self-aging replace commissioning?
No. Self-aging is a test function. Final commissioning still follows the manual and project acceptance procedure.
Source: ACS Series 1–20kVA UPS documents
Source: ACM Series 100–1200kVA Modular UPS
Related reading: UPS & Data Center FAQ | More UPS technical guides
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