Power from the car feeding back over USB

User feedbacks of the latest ESP32 based Freematics ONE+
StuH
Posts: 2
Joined: Mon Aug 07, 2017 6:53 pm

Power from the car feeding back over USB

Postby StuH » Mon Aug 07, 2017 7:02 pm

Hi,
In using the One+ while connected to a car (or regulated PSU) I have found that power is actually coming back across the USB serial connection into the host computer (see attached screenshot). While the voltage is low, I am concerned there is a risk of damaging the connected PC when debugging the device (to view the serial logs) if the vehicle sends a surge.

Can you confirm this is working as intended please. It seems (at first glance) that the device is missing a diode or two to prevent power feeding back up the USB cable.

Edit: It seems I cant attach an image to my post. The image shows a Legion power meter connected to the USB port of the One+, with no connection at the other end, receiving 2.8v across the wire.

stanley
Site Admin
Posts: 587
Joined: Sat Mar 01, 2014 3:15 am

Re: Power from the car feeding back over USB

Postby stanley » Sat Aug 12, 2017 12:06 am

This is true. The USB port can be used for power output. But no damage happens from my thousands hours of in-car debugging. If our device can't resist a surge, it won't last long when working unattended in car.


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