Pi 4 & Pi 400 USB current
The maximum current the Raspberry Pi 4 and Raspberry Pi 400 USB ports can supply is 1.2A total.
This 1.2A limit applies to:
- All USB ports combined: The four USB ports (two USB 3.0, two USB 2.0) share a total 1.2A budget.
- A single USB port: A single port can draw up to 1.2A if the other ports are unused.
Example scenarios:
- Four devices each drawing 0.3A = 1.2A total ✅
- One device drawing 1.2A = 1.2A total ✅
- Two devices each drawing 0.8A = 1.6A total ❌ (exceeds limit)
Understanding the limits
Why the 1.2A limit?
The Raspberry Pi 4 and Pi 400 use a 5V 3A power supply (15W total). Power is distributed as follows:
- Raspberry Pi board: ~1.0-1.5A under typical load (CPU, RAM, peripherals)
- USB ports: Up to 1.2A total for connected devices
- GPIO pins: Minimal (typically <0.1A unless powering HATs)
Under heavy load (CPU at 100%, all USB ports in use, GPIO devices powered), the Pi can draw close to the 3A power supply limit.
Protection: If USB devices try to draw more than 1.2A, the Pi's USB power management IC will limit the current to prevent overload. This can cause USB devices to malfunction or disconnect.
Power-hungry devices
Some USB devices draw more current than the Pi's USB ports can safely provide:
High-power devices:
- External hard drives (2.5" HDDs): Can draw 0.5-1.0A each
- USB fans or RGB accessories: 0.2-0.5A
- High-brightness USB lights: 0.5-1.0A
- Some USB-powered monitors: 1.0A+
- Fast-charging hubs or phone chargers: 1.0-2.0A+
Symptoms of insufficient USB power:
- USB devices disconnecting randomly
- External drives not being detected
- Under-voltage warning (lightning bolt icon) on screen
- Pi rebooting when connecting USB devices
Solutions for high-power USB devices
If your USB devices need more than 1.2A combined, use one of these solutions:
1. Powered USB hub:
- Connect a powered USB hub (with its own power supply) to the Pi
- Plug high-power devices into the hub instead of directly into the Pi
- The hub's external power supply powers the devices, not the Pi's USB ports
- Recommended: Look for USB 3.0 hubs with 2A+ per-port power supplies
2. External power for specific devices:
- Use a Y-cable for external hard drives (one USB plug for data, one for extra power)
- Power USB accessories from separate 5V power supplies
3. Upgrade your Pi's power supply (limited benefit):
- A higher-amperage power supply (e.g., 5V 5A) won't increase USB power beyond 1.2A due to hardware limits on the Pi itself
- However, it can prevent the Pi from being starved if USB and CPU draw power simultaneously
Best practice: For projects with multiple USB devices, always use a powered USB hub rather than relying on the Pi's built-in USB power.