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USB backfeeding


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A video I think some of you might find of interest, particularly in response to our discussion about the Ve-direct cable and not connecting the 5V pin, or accidentally backpowering your Pi/arduino from a usb hub. I once had a nervous moment after kicking out a polyfuse on a Dell laptop by accidentally reverse-powering via a usb hard-drive with a separate supply point. If this video is correct, it seems even some expensive computers don't have that level of protection.

 

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Yep I discovered the same using Arduino and the Pi. Remember the Arduino I fried the power regulator on. I figured out why. I have a 12v power supply connected to Arduino power socket. Then the Pi and Arduino is connected via usb. The Pi is powered by 5v. So what I found was if I remove the power from the Pi it does not die. It is getteng power from the Arduino and the power regulater then starts to get very hot. If i dont disconnect it it will fry the power regulator. So now I need to figure out a way to stop that from heppening. I need to test that if I use the gpio pins to connect the 2 if this is still the case and if I can still program the Arduino from the Pi using the pins. All works the way I want it accept if the Pi's power goes off. Then I will fry the Arduino. 

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21 minutes ago, jdp said:

I need to test that if I use the gpio pins to connect the 2 if this is still the case

Microcontrollers often have reverse-biased diodes on io pins for protection (ESR etc), so a test is definitely in order :-)

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I use a powered HUB, but not connected to Eskom. I think before I ever connect it again to Eskom, I am going to test it like in the first video. And will do that with every HUB I buy from now on.

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Eskom has nothing to do with it. Two 5v supplies powering the same extended bus with slightly different accuracies is the problem. For example, one sees 4.8v and tries to pull it up to 5v. The other sees 5.1v and tries to sink it down to 5v. In the middle they are attempting to short out 0.3v at whatever current can be mustered... :-)

Sent from my GT-I9195 using Tapatalk

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You can use the hub without the external supply, using power from the host computer. You can also use the hub with the external supply, but then you have to cut the 5v line on the board or in the cable.

Sent from my GT-I9195 using Tapatalk

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