Voltage output of the USB C ports

Hello, my name is Lorenzo from Italy and I have just got an EB70 to power my astrophotography setup. It is not clear to me how the USB C ports work. I have seen it can provide up to 100W but what’s the voltage. I tried to measure the output voltage and found 0.8 V. I would like to use this port to power a miniPC requiring 12V / 3A, so within specifications. The others 12V outputs are already used.

Thank you!

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Hi Lorenzo,
I haven’t measured it on Bluetti devices yet, but USB-C is normally based on USB 3 spec; USB power delivery aka “PD” uses a process called “power negotiation” to determine what voltage and current to use. This is a complex process, but easy to summarize:

  1. Initially, when a device is connected, it can draw a small amount of power (up to 5V at 100 mA).
  2. The device then requests more power by sending a structured message to the host or charger.
  3. The host or charger either accepts the request or offers an alternative that it can support.
  4. Once both sides agree, the host or charger changes its output to the negotiated voltage and current.

With USB PD, the voltage can be negotiated up to 20V, and the current up to 5A, depending on the capabilities of both the device and the host or charger. This enables faster charging and supports more power-hungry devices.

The low 0.8V you measured is OK since it’s the “standby” voltage, as the charger is waiting for a device to power. It can’t provide the full voltage (19-20V) until is has confirmation the device can handle it. For instance, a basic smartphone still recharges on 5V, which is the USB default voltage.

To ensure the voltage is matching your expectations, it’s always handy to have one of those:

You can find them on Aliexpress (link) for a few euros.