USB-C port on UPS stops charging devices via USB hub after a few seconds

Understanding USB-C Charging Limitations on Uninterruptible Power Supplies (UPS): A Technical Perspective

In today’s connected environment, uninterruptible power supplies (UPS) are critical for safeguarding electronic devices against power interruptions. Many users leverage UPS units not just for backup power but also for device charging, utilizing built-in USB-C ports to replenish smartphones, wearable devices, and peripherals. However, some users encounter challenges where such USB-C ports cease to support continuous charging when connected through certain hubs or devices.

Case Study: Troubleshooting USB-C Charging Issues with a CyberPower UPS and UGREEN USB Hub

A recent user experience illuminates this issue well. The individual owns a CyberPower CP1500PFCLCD UPS, which features a USB-C port rated to provide 5V at 3.1A—sufficient for charging small devices like a Garmin Forerunner 255 watch. To expand charging capabilities, they purchased a UGREEN Revodok USB hub (model CM818) to connect multiple devices through the UPS’s USB-C port.

Initial observations indicated that when connecting the USB hub to the UPS, along with a device such as the Garmin watch or other peripherals (e.g., Bluetooth speakers or smartphones), charging was interrupted after approximately two seconds. Repeated attempts of unplugging and replugging the hub or devices did not resolve the issue; the devices would briefly charge before the process stopped. Notably, connecting the same hub directly to a desktop computer’s USB-C port resulted in successful, sustained charging for all connected devices, confirming the hub’s functionality.

Furthermore, testing the UPS’s USB-C port directly with a smartphone demonstrated reliable, uninterrupted charging, suggesting that the port itself is functioning correctly. The problem appears specific to the interaction between the UPS, the USB hub, and certain devices.

Technical Analysis

Several factors can contribute to such charging disruptions:

1. Power Delivery (PD) Negotiation:
   The USB-C standard involves dynamic power negotiation. Many hubs and devices rely on proper handshake protocols to determine power levels. The UPS may not support the latest or full USB PD specifications, causing the hub or connected devices to terminate charging prematurely.

2. Voltage and Current Compatibility:
   Although the UPS’s USB-C port is specified at 5V/3.1A, real-world implementation may vary. Some hubs demand higher or more stable current, which may not be reliably supplied during certain conditions.

3. Hub Compatibility and Standards Support:
   Not