USB Power Surge

I have two Beaglebone Blacks connected to my PC via a USB hub. When I connect the hub to the PC, both boards power up and I can open an SSH to each. Both run fine with no problem at all.

I’ve configured UART4 and UART5 on both boards and connected the boards via both serial ports crossing over the RX and TX lines.

For UART4 I’ve connected pins P9-11 (RXD) and P9-13 (TXD)
For UART5 I’ve connected pins P8-38 (RXD) and P8-37 (TXD)
I’ve also connected pin P8-1 (GND).

I’ve written a C library that uses termios to read and write to the serial port and I call this from Java usng JNI. Everything is find and works ok, but after a short period on of the BBB goes down and I get a message appear on the PC reporting a power surge on the USB hub. I cannot get the board to power up after this despite unplugging and plugging in the USB connection to the board, only power cycling the hub will restore power.

The problem seems to be related to the serial I/O. Can anyone explain this? Have I done something wrong?

Thank you.

Well, what do these serial lines connect to?


The two beagle bones are connect to each other, so on one board,

P9-11 (RXD) on BBB1 is connected to P9-13 (TXD) on BBB2.
P9-13 (TXD) on BBB1 is connected to P9-11 (RXD) on BBB2.

P8-38 (RXD) on BBB1 is connected to P8-37 (TXD) on BBB2.
P8-37 (TXD) on BBB1 is connected to P8-38 (RXD) on BBB2.

P8-1 on BB1 is connected to P8-1 on BBB2.

Thats it.

Are they powered from the same power supply?


Yes, and the USB hub has its own power supply.

Hmmm. So, why would there be a surge on the PC side of the HUB is self powered? Or is the HUB detecting the power surge on one of the ports? The current is very close to 500mA.on the board depending on what you are doing. My suggestion is to switch to external DC supplies and make sure you have the grounds of the two boards tied together.


Thank you for the reply.

I’ve seen a message box popup up on the PC for a split second warning of the power surge. The GND is connected between the boards, but unless the GND is through the USB connection I haven’t provided and external GND.

I will try using external power supplies, can you recommend a low cost PSU / Adapter available from Farnell?

Thank you,

Not sure exactly what Farnell has. Make sure it is at least 5V at 1A. Similar to the one described here


Thank you.

A power surge message from the hub is detected by the PC. Unfortunately many powered Hubs take the spec too seriously and fuss when 500ma is reached. Other Hubs have a more relaxed point of view.
For example, I have a D-LINK DUB-H7 which notices 500ma and I stopped using it in microcontroller experiments.
But a Staples 12416 will supply 1A per port and 3.5A overall with no problem. I use the Staples on my bench.
I also have a noname chinese unpowered Hub which directly connects all the 5v lines (a cheapo error). I plug the chinese Hub into my Staples and plug another 5v 2.5A wart into the cheapo. Now I have 6A overall. I have drawn 1.5A from a port on the cheapo with no problem.

Notice that the smarter the Hub, the worse the results :slight_smile:
DO NOT plug you Beaglebone or other micro directly into your PC or Laptop.

I’ve now ordered one of these to power my BBB’s: