My PC runs normally on utility power, but it sometimes shuts down and restarts when the inverter takes over during a power cut. The setup uses a Corsair CX550 PSU, a pure sine-wave inverter rated around 900 VA/700 W or more, and a 240 Ah battery. The PC draws roughly 316 W while gaming, so the inverter is not overloaded. When the power fails during gaming, the PC and monitor turn off for about 5–8 seconds, while the inverter remains running. If the PC is idle, it usually stays on. The inverter has also occasionally beeped as though utility power disappeared even when I did not notice an outage, and the PC has sometimes restarted while mains power was available. I am considering an APC Back-UPS BX600C-IN and would place it between the inverter and the PC, using the inverter as the UPS input. Would an offline/standby UPS help bridge the inverter's transfer time, or would two switching devices cause more problems?
2 Answers
An offline UPS may not solve this reliably. Its own transfer switch could add another interruption, and some standby UPS units may not like the inverter's output or may repeatedly switch between modes. An online UPS avoids the transfer gap because it continuously powers the computer through its inverter, but it is usually much more expensive. A transfer interruption of around 10 ms can be enough to upset some PC power supplies.
The CX550 is not one of the stronger power supplies, and a better-quality unit may have more hold-up time while the backup source takes over. Since the computer also restarts occasionally when mains power is available, the PSU itself should be treated as a possible fault rather than assuming the inverter is solely responsible.
An online UPS is outside my budget, while the standby model is affordable. The inverter also sometimes beeps as if utility power has disappeared even when there was no obvious outage, so I suspect its input detection or transfer behavior may be part of the problem.